Disturbance to waterbirds wintering in the Stour-Orwell estuaries SPA

6th December 2007

Neil Ravenscroft1, Bill Parker2, Rick Vonk3 & Mick Wright4

A Report from Wildside Ecology to the Suffolk Coast and Heaths Unit

1 Wildside Ecology 4 Kingshill Brandeston Road Earl Soham Suffolk 1P13 7RY

2Suffolk Coast & Heaths Unit Dock Lane

MeltonWoodbridge

Suffolk IP12 2PE

3 RSPB Unit 13, Court Farm 3 Stutton Road Brantham Suffolk CO11 1PW

4Suffolk Wildlife TrustBrooke House

AshbockingIpswich

Suffolk IP6 9JY

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Foreword The Stour and Orwell estuaries are designated as a Special Protection Area (SPA) under European Law because of the number of birds and range of species that are present on the estuaries during winter. The area is popular for recreation as well as a centre of commercial activity. Little is known about the impact of the current levels of this activity on bird populations. The intensity of these activities is expected to increase as further industrial and residential development around the estuaries hinterland is planned. The Stour and Orwell Estuaries Management Group1, is a partnership of more than 20 organisations that aims to;

“Promote the sustainable use of the Stour and Orwell estuaries through the management of human activity, in a way that is compatible with the conservation of the estuarine ecosystem”.

It recognises that, in order to manage the estuary in a balanced way, evidence based on scientific research is essential to support initiatives designed to protect the special nature of the area. This report provides part of the evidence to facilitate sustainable recreation in the estuaries whilst protecting the natural environment. Working with a range of organisations and local communities it is intended to utilise the learning from this work to develop both overall guidelines and also resolving site-specific issues. This research project was co-ordinated by the Suffolk Coast and Heaths Unit and was developed, organised and funded by a range of organisations all working to ensure the protection of the special features of Stour and Orwell estuaries now and into the future.

1 see www.suffolkcoastandheaths.org Tidal Suffolk section

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Summary 1. The distribution of recreation and other activities and the disturbance they caused to

birds were measured on the Stour and Orwell over the three winters from 2004/05 to 2006/07. 540 hours of observations were undertaken at fifteen sections incorporating 9.75km (17%) of the estuaries.

2. The Orwell was busy compared with the Stour (about four times as busy) but birds on

the Stour were generally more sensitive to activity and more prone to leave study sites (one in six events caused disturbance on the Orwell, one in three on the Stour).

3. Walkers, those with dogs, and boats were the most frequent activities on the SPA.

These also caused most of the disturbance that was recorded but birds were most sensitive to relatively infrequent events such as shots, aircraft and baitdiggers which displaced greater numbers of birds.

4. The impact of activities was site-specific and related to their number, the state of tide,

number of birds present, width of mudflat and upper shore characteristics. Events on the shore caused most disturbance at high tide and events occurring in the estuary most at low tide. There was twice as much disturbance at high tide.

5. Birds appeared to habituate to benign events such as sailing boats, vehicles and

horses and little disturbance was caused by these events where they were most frequent. But there was strong evidence that apparent habituation to more disruptive events was actually the result of reduced bird numbers. Fewer birds occurred where the number of activities was greatest, especially at high tide.

6. Low disturbance frequencies occurred therefore where birds numbers were either:

a) relatively unaffected by activities (most of the mudflats of the Stour, the wider mudflats of the Orwell (above 400m) and a few isolated roosts on both estuaries); b) severely affected by activities (parts of the northern shore of the Orwell at high tide, areas close to car parks or housing at both states of tide and narrow mudflats on the Orwell at low tide).

7. The greatest disturbance occurred on mudflats on the Orwell that are favoured

feeding areas for birds but where visitor levels were high. Hidden approaches, relatively small mudflats and access to the shore at low tide compounded these effects.

8. Overall, birds in most parts of the SPA, particularly on the Stour, are affected little by

the majority of activities at low tide. Fewer events, the larger numbers of birds and the availability of alternative areas on the estuary probably caused the increased sensitivity of birds on the Stour. By contrast, the high levels of activity around most of the Orwell, the relatively low numbers of birds at high tide and comparatively small mudflats at low tide, suggest that disturbance may be having an impact on populations of birds in this estuary.

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Contents Foreword 1 Summary 2 1. INTRODUCTION 1.1 Background 6 1.2 The ornithological status of the Stour-Orwell estuaries 6 1.3 Birds and disturbance in estuaries 7 1.4 Objectives 9 2. METHODS 2.1 Characteristics of the estuaries 10 2.2 Characteristics of the study sites 10 2.3 Counts 10 2.4 Terminology, data presentation and analysis 12 3. RESULTS 3.1 Distribution of birds, events and disturbance 13 3.2 Activities & disturbance 14 3.3 Principal activities 15 3.4 Factors affecting birds 16 4. DISCUSSION 4.1 Distribution of events 18 4.2 Rates of disturbance 18 4.3 Activities and disturbance 19 4.4 Effects of landscape 19 4.5 Habituation 20 4.6 Other effects of disturbance 21 4.7 The potential impacts on bird populations of the SPA 22 4.8 Conclusions 23 5. Acknowledgements 24 6. References 24 7. Tables 28 8. Figures 36 9. Appendices

1. Maps of study sites 49 2. Guidance notes and recording sheets issued to counters 55 3. Literature on bird disturbance and the Stour-Orwell estuaries 60

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List of Tables Table 1: Features of the study sites on the Stour and Orwell estuaries 2004/005 to

2006/07. Table 2: The counts undertaken at the study sites. Table 3: The frequencies of events and events causing disturbance at the study sites

over all tides. Table 4: The overall numbers of activities and events causing disturbance throughout

the study. Table 5: The numbers of activities and events causing disturbance at high and low

tides. Table 6: An indication of the relative sensitivity of species to disturbance on the

estuaries through comparison of the presence of species in background and disturbance counts.

List of figures Fig. 1: The distribution and approximate extent of the sites studied on the Stour and

Orwell estuaries. Fig. 2: The mean numbers of birds recorded during background counts in the study

sections of the estuaries. Fig. 3: The frequencies of events on the estuaries over the three winters (top) and

the frequencies of events that caused disturbance (bottom). Fig. 4: The effects of season on activities and disturbance. Fig. 5: The effect of tide on the response of birds. Fig. 6: The occurrence of activities and the disturbance they caused at high and low

tide. Fig. 7: The mean response of birds to walkers and those with dogs at high and low

tide on the estuaries. Fig. 8: The response of birds to different numbers of dogs. Fig. 9: The mean response of birds to different groups of motor vessel at high and

low tide on the estuaries. Fig. 10: The mean responses of birds to activities at the study sites. Fig. 11: The relationship between the number of category events recorded in the study

and the frequency with which they caused disturbance. Fig. 12: The mean numbers of birds displaced by different activities.

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Fig. 13: The relationship between the numbers of events at sites and the disturbance caused to birds.

Fig. 14: The relationships between the number of category events at sites and the rate

of disturbance to birds. Fig. 15: The mean number of birds per count at all states of tide in sections of the

Stour and Orwell estuaries compared with the level of activity recorded.

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1. Introduction 1.1 Background

The Stour and Orwell estuaries are situated in the most easterly part of the British Isles and are a vital part of the Eastern Flyway for migrating wildfowl and waders. They provide wintering habitats for important wetland bird species and are recognised as a wetland of major international importance comprising extensive mudflats, low cliffs, saltmarsh and areas of vegetated shingle (JNCC 2001). They qualify as a Special Protection Area (EEC Directive 79/409 on the Conservation of Wild Birds) and Ramsar site (Ramsar Convention on Wetlands of International Importance) on the basis of their wintering waterfowl populations.

The estuaries are separate for most of their tidal lengths, but merge and share a mouth into the North Sea that includes Europe’s fourth busiest container port at Felixstowe. Ipswich, the county town of Suffolk and another port, is situated at the head of the Orwell which is relatively narrow. By contrast, the Stour is wide and relatively shallow. The estuaries are located in a predominantly rural environment but the area has been granted ‘growth point’ status and this is predicted to bring an additional 50,000 jobs / homes to the area by 2020. This has significant potential to increase the pressures on both the habitats and species of the Stour-Orwell.

In order to address many of the pressures on the estuaries the ‘relevant authorities’ (i.e. those organisations who have statutory powers over the estuary) and other key stakeholders have formed the Stour and Orwell Estuaries Management Group (S&OEMG) to provide a forum to resolve issues. This group consists of Local Authorities, Government Agencies, commercial organisations and NGOs, all of which have a particular interest in the estuaries (see www.suffolkcoastandheaths.org - Tidal Suffolk section).

1.2 The ornithological status of the Stour-Orwell estuaries

In the five winter period of 2000/2001-2004/05 the SPA supported an average peak count of 72993 birds at high tide (53012 on the Stour and 19981 on the Orwell) and twelve wader or wildfowl species were present on one or other estuary in national or internationally important populations (>1% of GB and East Atlantic populations respectively) (Banks et al 2006). The status of both estuaries has decreased in recent years since large numbers of birds occurred during a series of cold winters in the 1980s (Wright 2001). Based on the most recent count data, the Stour has lost international status for dunlin and golden plover and its national status for wigeon, ringed plover, lapwing and curlew, and the Orwell has lost national status for shelduck, grey plover and dunlin since 1999 (SWT 2007). One species has gained national status in the same period – turnstone on the Stour. Furthermore, most of the 17 bird species listed in the SPA citation have British Trust for Ornithology Alert Status: i.e. their numbers have fallen significantly in the estuaries over 5, 10 or 25 year time periods (Armitage & Rehfisch 2002).

Apart from the possibility that there are long-term fluctuations in the bird populations of the estuaries, there are many potential causes of the recent downward trend in numbers. 1) The prolonged effects of losses of habitat to development or erosion on the estuaries (the Orwell has lost large areas of mudflats at its mouth to port development and the saltmarsh area of both estuaries has been reduced by about half in recent years – Cooper et al 2000). Loss of habitat ultimately affects the size of the population of wintering waders (Goss-Custard et al 1995); 2) Dredging activity at Harwich may have had an impact on the hydrodynamics of the estuaries (despite a programme of mitigation works) and affected the deposition of

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sediment (PDE 1998) (the composition of invertebrate and bird faunas reflect the sediment composition of mudflats – Yates et al 1993); 3) Global warming may be affecting the patterns of migration of wintering birds but the effects of this on local populations are yet to be established (birds may not be travelling as far south to winter owing to warmer temperatures – Austin & Rehfisch 2005); 4) Recent changes in water quality, particularly on the Orwell (improvements reduce the quantity of food available to birds – Burton et al 2002a); 5) Disturbance from recreational activities (continual disturbance reduces numbers of birds and the habitat quality of estuaries, Burton et al 2002b). The level of recreation on the estuaries is thought to be relatively high (boating, bait digging, shooting, walking etc) as is the commercial activity associated with the ports of Felixstowe, Harwich and Ipswich but there is little information available about the disturbance that this may cause to wintering birds. The relatively low numbers of birds roosting beside the Orwell at high tide compared with those feeding at low tide suggest that the effects of disturbance, at least at high tide, may be severe (Armitage et al 2003), as birds prefer to roost close to their feeding grounds (Symons & Langslow 1986, Rehfisch et al 2003).

1.3 Birds and disturbance in estuaries Human activity has clear impacts on the distribution and success of birds breeding in coastal areas (Anderson & Keith 1980, Erwin 1980, Keller 1988, Verhulst et al 2001, Bolduc & Guillemette 2003, Beale & Monaghan 2004a), but its effect on birds wintering in estuaries is a complex issue, partly because the response of birds to human and other activities varies greatly from site to site (Davidson & Rothwell 1993, Taylor et al 2005). Aircraft, vehicles, baitdiggers, boats, walkers and dogs are usually the most common winter activities in estuaries (Owen 1993, Smit & Visser 1993, Musgrove et al 2003), but aircraft may have large effects on bird behaviour in some places (Smit & Visser 1993) and little in others (Burger 1981). Likewise, vehicles, baitdiggers, walkers and dogs may be primary sources of disturbance at some sites (Owens 1977, Madsen 1985, Kirby et al 1993, Townshend & O’Connor 1993, Klein et al 1995) but not others (Burger 1981, Owen 1993, Smit & Visser 1993, Fitzpatrick & Bouchez 1998). The responses of birds may also vary temporally, and they are often more sensitive early in the winter (Owens 1977, Madsen 1985, Belanger & Bedárd 1989, Stillman & Goss-Custard 2002). This may be because birds appear to habituate to regular, non-threatening activities or noises (Owens 1977, Davidson & Rothwell 1993, Smit & Visser 1993, Madsen 1995, Hill et al 1997), and this may explain why resident birds are less responsive to human activity than newly-arrived migrants (Koolhass et al 1993, Klein et al 1995). Some species are also disturbed more readily than others and take flight at larger distances (Burger 1981, Smit & Visser 1993). The habits of some birds also make them more vulnerable to disturbance e.g. those that feed in large flocks appear highly sensitive (Madsen 1985, Smit & Visser 1993, Gill et al 1996), while those that are primarily water-based are less prone to disturbance (perhaps as water conveys a safety advantage, Burger 1981).

Although bird behaviour may be altered by the presence of human or other activities, disturbance may not always impact on individual birds or their populations. Estuarine birds are able to compensate for lost feeding time or poor conditions by feeding at different times (for example at night, Belanger & Bedárd 1990), increasing their feeding rate (Swennen et al 1989, Fitzpatrick & Bouchez 1998, Atkinson et al 2007), feeding for longer (Stillman & Goss-Custard 2002) or feeding elsewhere or in different habitats (Goss-Custard & Verboven 1993, Gill et al 1996, Smart & Gill 2003). Indeed,

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birds may only respond readily to disturbance because alternative areas are available to them (Gill et al 2001). Well-fed turnstone are disturbed more easily because they are in better condition and able to avoid any risk posed by disturbance (Beale & Monaghan 2004b). On the Exe estuary, oystercatchers are disturbed more easily when they are able to compensate for lost feeding time, but become less responsive as energy requirements increase later in the winter and birds need to feed more (Stillman & Goss-Custard 2002). Therefore, the observed behavioural response of birds to human or other activity may not always reflect an impact on the fitness of birds. The ability of birds to compensate for lost feeding means that disturbance probably does not impact on estuary populations where it occurs at relatively low levels. Even the displacement of birds may not be detrimental, and high rates of disturbance may only cause impacts when food is scarce i.e. later in the winter (Goss-Custard et al 2006). But in areas where there are no alternatives, birds may have no option other than to endure disturbance, and the interference this causes with feeding and roosting, because they are having difficulty meeting their energy requirements. However, even low rates of disturbance may affect bird survival if this is spread over large areas of an estuary and greatly reduces the amount of available habitat (West et al 2002). And young birds may be affected unduly by disturbance as they are the least efficient foragers (Goss-Custard & Verboven 1993). Species with restricted feeding times may also be affected severely by disturbance, such as wigeon that may only feed when Zostera is exposed for a short period at low tide (Fox et al 1993). Altered feeding behaviour such as night-feeding may also not compensate birds fully for interruptions caused by disturbance (Belanger & Bedárd 1990, Goss-Custard & Verboven 1993). Repeated disturbance reduces the fitness and numbers of birds at sites, and at all temporal and spatial scales. The effects may be temporary (fewer birds are present when there is disturbance – Burger 1981, Koolhaas et al 1993), delayed (numbers may be reduced for a day or so after disturbance – Belanger & Bedárd 1990) or permanent (densities of birds are lower in areas or entire estuaries where human activities are greater – Madsen 1998a, Burton et al 2002b, c). In this respect, disturbance may seriously reduce the habitat quality of an estuary (Burton et al 2002b). Ultimately, repeated disturbance may have significant impacts on the energetics of estuarine birds, their condition and ability to survive the winter, as well as potential knock-on effects on their ability to migrate and breed (Goss-Custard & Durrell 1990, Belanger & Bedárd 1990, Davidson & Rothwell 1993, Madsen 1995, Atkinson et al 2007). When this occurs, the impacts of disturbance may be equivalent to habitat loss (Cayford 1993, Madsen 1995, Hill et al 1997, Stillman et al 2007) that is known to reduce the survival of displaced birds and affect population size (Goss-Custard et al 1995, Burton et al 2006). Unlike habitat loss, the effects of disturbance on the quality of an area for birds are reversible. Many studies have shown that bird numbers increase when the source of disturbance is removed or mitigated (thereby also demonstrating its initial impact). The creation of refuges from shooting result in large influxes of wildfowl, both at the local (Madsen 1998b) and national scale (Mooji 1991) and numbers of feeding birds increase when bait-digging is restricted or stopped (Townshend & O’Connor 1993). Numbers of wildfowl have increased dramatically at Trimley Marshes on the Orwell since its conversion to a nature reserve (Wright 2001).

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1.4 Objectives Disturbance by recreation in the Stour-Orwell estuaries is one of the factors with the potential to affect the integrity of the SPA that might be most easily managed, but there is little evidence available with which to make informed decisions. Information on the effects of recreation is integral to the planning of future access to the SPA and perhaps the mitigation of the impacts of current access arrangements. Therefore, the S&OEMG initiated research to gather data on recreation and disturbance to birds in the Stour-Orwell estuaries SPA. The objectives of this research were: 1. Measure the level of activity on and around the Stour and Orwell estuaries; 2. Assess the level of disturbance to wintering birds from these activities; 3. Identify areas where disturbance may be impacting on bird populations.

Ultimately, it is intended that the work contribute to the development of multi use visitor management plan for the Stour and Orwell that will include work with specific interest groups to reduce the level of impact, target topics for general interpretation and develop infrastructure at vulnerable locations. The publication of this report will also contribute to the wider debate on Coastal Open Access that is being developed currently by Natural England.

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2. METHODS 2.1 Characteristics of the estuaries

With the exception of small parts of the estuaries, most of both the Stour and Orwell are accessible by the public. Footpaths run along the edges of both estuaries where there are sea walls and through fringing saltmarsh, fields and woodland where there are not. At low tide, remaining areas become accessible owing to upper shores that are composed of sand and shingle. Access to the estuaries by road is limited and there are only small stretches beside the upper Orwell (about 2km) and at Mistley on the upper Stour. Public roads lead to the shore at the villages of Shotley Gate and Pin Mill and the marinas at Woolverstone and Levington on the Orwell, and there are a few minor access roads and private tracks to parts of the shore of the Stour. Car parks have been provided for visitors to the Orwell Country Park at Bridge Wood and Piper’s Vale, which also provide access to the estuary, and elsewhere there are car parks at Nacton and Levington on the Orwell and Holbrook Bay and Wrabness on the Stour. These features are the primary access points for visitors to the estuaries, but remaining parts of the estuaries are accessible by footpaths that run in from other villages and roads further inland. There is more boat traffic on the Orwell than the Stour, owing to the docks at Ipswich, and the presence of marinas, boatyards and sailing clubs at Bourne Bridge, Freston, Woolverstone, Pin Mill, Levington and Shotley Gate. Traffic on the Stour is limited to commercial activity at Harwich and lesser activity at Holbrook Bay and Manningtree.

2.2 Characteristics of the study sites The study incorporated fifteen sites spread along the Stour and Orwell estuaries (ten on the Orwell and five on the Stour, fig. 1). Sites were selected to represent a variety of pressure points. All study sites were accessible by the public and all bar one had access routes along the entire foreshore of the study area, either via a seawall, paths on adjacent land or on the shore itself (Table 1 and appendix 1). The exception was Freston where public access was restricted by a single path perpendicular to the shore (although walkers used this to access the length of the shore). The isolation of sites varied, and some sites (Stutton on the Stour and Crane’s Hill on the Orwell) were relatively remote, being at least 1.5km from the nearest village or car park and accessible only by footpath. Other sites were in areas where visitors were encouraged either by the provision of car parks and easy access routes (Nacton and Bridge Wood on the Orwell, Holbrook Bay on the Stour) or the proximity of villages or urban areas (Pond Ooze, Pin Mill, Levington and Shotley Point on the Orwell and Erwarton Bay on the Stour). Three sites (Levington, Thorpe Bay and Shotley Point) were adjacent to marinas on the Orwell. Remaining sites on the southern Stour (Bradfield and Jacques Bay) were accessible by tracks and footpaths. The mudflats of study sites at low tide were generally wider on the Stour than on the Orwell (up to 1250m at Holbrook Bay and over 750m at Bradfield and Jacques Bay on the Stour). The largest studied on the Orwell was 625m wide (at Alnesbourne) and most were less than 400m (those at Shotley and Crane’s Hill were only about 125m wide).

2.3 Counts

Site extent The extents of sites were demarcated by observers using landmarks and usually incorporated a 500m stretch of shoreline and mudflat, but owing to the shape of the shore and availability of landmarks the length of shoreline was larger at some sites (the largest incorporated 1250m of shoreline, Table 1). In total, the study sites

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incorporated 9.75km of the shoreline of the estuaries, representing about 17.3% of the SPA (6.5km or 25% of the Orwell and 3.25km or 10.4% of the Stour). Number and duration Six sites were studied in each of three winters – 2004/05, 2005/06 and 2006/07. One site (Freston) was included in all three winters and another (Levington) was studied in the first two winters. Ten visits were made to each site throughout the winter. The dates on which sites were visited varied in the first winter, but attempts were made thereafter to undertake two counts in each of the five winter months (November-March inclusive) in order to standardize as far as was possible the conditions under which sites were assessed (Table 2). To provide information on recreation at different states of tide, counters in the second and third winters were asked to undertake one count at or close to high water and one count at or close to low water each month (Table 2).

Each site visit was composed of three hours of recording, so 30 hours of observation was undertaken at each site per winter, resulting in a total of 180 hours per winter on the estuaries and 540 hours over the course of the study. Bird counts Two types of count were undertaken. 1. Background counts: at the start of each visit, the observer made a count of the number of each species of bird in the study area and thereafter undertook repeat counts hourly until the end of the three-hour period (half-hourly in the first winter). 2. Disturbance counts: observers counted the number of each species of birds disrupted when an event caused disturbance during the three-hour period. Observers also ranked the response of birds to the event on a scale that reflected the degree of disruption caused by the event (disturbance index d): 0 no disturbance to birds; 1 minor disruption – birds walk or fly but return to proximity of previous position; 2 local displacement – birds take flight and return to a different position in the study area; 3 major displacement – birds take flight and abandon the study area. Activities All shore-, water- or air-based activities (events) that occurred within the study area and the three-hour period, were recorded, regardless of whether they caused disturbance to birds, and observers noted the time and a description of the event. The nature of some events (e.g. shots and some air- and water-based activities) meant that it was necessary to record occasional events outwith the study site if they caused disturbance to birds. In most cases, the source of disturbance was clearly linked to disturbance to birds (e.g. a baitdigger walking on a mudflat or a dog running down the shore) but in others, the coincidence of disruption to birds with an activity (e.g. a walker on the foreshore, a plane overhead or a boat on the water) was assumed to be causal. Activities were placed into the following categories for analysis: 1. walkers (WA); 2. walkers accompanied by dogs (WD); 3. joggers (JO); 4. cyclists (CY); 5. baitdiggers (BA); 6. people (PE): remaining events (stationary or slow moving) on the foreshore or seawall (birdwatchers, fishermen, boatmen, horse-riders);

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7. shooting (SH); 8. motor vehicles (VE); 9. motor vessels (MV) (incorporating motoring yachts, speedboats, other launches, container ships, customs vessels, dredgers etc); 10. sailing vessels (SV) (dinghies and yachts); 11. aircraft (AIR) (helicopters, jets, light aircraft and micro-lites); 12. raptors (RA) (including events caused by other large birds); 13. and remaining events (two canoeists, six loud noises, a rocket and a plastic bag blowing across a mudflat) were categorised as other (OT). Dreads, or seemingly unprovoked displacement of by birds, were also recorded.

2.4 Terminology, data presentation and analysis Site size was accounted for in the calculation of event and disturbance frequencies as larger sites were more likely to contain additional access points that might have an effect on the number of events that took place. The frequencies of events (e) and events that caused disturbance (de) were represented as the number per hour per 500m of shore when comparing data from different sites. Whether size of site actually influenced the number of most events that were recorded at sites is debatable. Most activities took place parallel to the site – either along the shore or along the estuary channel – and as such, small differences in site size probably had no influence on activity levels. There was no overall relationship between site size and number of events recorded (rs = 0.18, n = 15, ns). But some activities that take place perpendicular to the shore, such as baitdiggers and raptors, might be expected more often on larger sites. The response (or sensitivity) of birds was expressed as the mean of disturbance indeces 0-3 (mean d). The extent of disruption to birds during events that caused disturbance was expressed as the mean of disturbance indeces 1-3 (mean i). The mean numbers of birds present on sites and the mean numbers affected during disturbance were calculated from the background and disturbance counts. Analysis of overall activity included all counts (n = 180, Table 2), but comparisons of disturbance at high and low tides reduced the number of counts available to 149 (as 31 counts took place on rising or falling tides). All means are presented with standard errors. Percentages used in statistical tests were converted to arcsines before analysis and re-converted to percentages for presentation. Owing to the ranks applied to disturbance, and the large variation in sizes of populations of birds at different sites, non-parametric statistics are used throughout: Spearman’s correlation coefficent (rs) for the investigation of linear relationships; Mann-Whitney U test (Wilcoxon rank-sum test) for the comparison of two samples; and the Kruskal-Wallis 1-way ANOVA by ranks (H) for the comparison of several samples.

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3. RESULTS 3.1 Distribution of birds, events and disturbance

Distribution of birds Birds were more concentrated at high tide and the primary roosts occurred at Levington and Freston on the Orwell and Stutton and Holbrook on the Stour (fig. 2). There were few birds at high tide at Nacton and Bridge Wood on the Orwell and Erwarton Bay on the Stour. Birds were spread more evenly at low tide, but relatively few occurred at Bridge Wood, Crane’s Hill and Shotley on the Orwell (fig. 2). Distribution of events/activities Events occurred at all sites, and only three of the 180 counts recorded absolutely no activity (1.7%) – one at Freston on the Orwell in November 2005 and one each at Stutton and Bradfield Bay on the Stour in March 2007. The overall activity rate was 5.0±1.1 events per hour per 500m of shore but levels of activity were much lower at sites on the Stour (site mean 1.9±0.8 events per hour per 500m), especially in the upper reaches of the estuary (fig. 3), compared with the Orwell (6.5±1.4 events per hour per 500m) (U = 7.0, n = 15, p = 0.03). Pin Mill (mean 14.0±1.8, peak 24.3 events per hour), Nacton (mean 12.4±1.2, peak 19) and Bridge Wood (mean 9.7±0.8, peak 12.7), all on the Orwell, were by far the busiest parts of the estuaries (H = 161.0, n =180, p<0.0001, fig. 3). High event rates occurred occasionally at other sites on the Orwell (e.g. peaks at Levington and Thorpe Bay of 15.7 and 10.9 per hour) – Freston had the lowest event frequency on the Orwell (mean 1.3±0.1, peak 3.7 per hour). Means of less than 3 events per hour were recorded at all sites on the Stour and the peak count was 5.7 events per hour at Erwarton Bay. Vehicles on the adjacent public road were the largest component of activity at Pin Mill (7.5 per hour and 53% of all activity) and otherwise activity at this site was relatively normal (Table 3). Elsewhere vehicles were rare, although they accessed the shore at Bradfield Bay, and motorbikes were recorded on the seawalls at Alnesbourne, Levington and Erwarton Bay. Activities on the shore or seawall were the primary feature of remaining sites. Walkers and those with dogs were ubiquitous and joggers and cyclists occurred at most sites (Table 3). By far the greatest rates of activity by people on the shore or seawall were on the northern shore of the Orwell at Nacton (9.6 events per hour, peak 17.3 per hour), Bridge Wood (6.5 events per hour, peak 9) and Pond Ooze (5.2 events per hour, peak 9.3, where joggers were a prominent feature). Baitdiggers were scattered throughout both estuaries at low tide and occurred at most sites at rates of below one per hour per 500m of shore. Boats on the estuaries occurred at most sites, and their distribution bore no relation to the proximity of marinas and other facilities, as they were not particularly frequent at Shotley, Levington or Pin Mill, but they were more frequent on the Orwell than on the Stour. Remaining activities were infrequent but scattered throughout both estuaries. Distribution of disturbance No site was undisturbed. Disruption to birds was recorded at an overall rate of 1.0±0.2 disturbance events per hour per 500m of shore and there was no difference between the estuaries (Orwell 1.1±0.3 disturbances per hour, Stour 0.7±0.1, U = 34.5, n = 15, ns). The frequencies of disturbance were particularly high at Bridge Wood (3.6 per hour per 500m, peak 5.7) and also Pond Ooze (1.7 per hour, peak 3.7) and lowest at Shotley and Jacques Bay (both 0.2±0.1 per hour) (fig. 3, H = 71.8, n = 180, p<0.0001). Remaining sites were in the range of 0.4-1.1 disturbances per hour,

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but high peaks were also recorded at Alnesbourne (5.3 per hour and Levington 3.7 per hour). People on the shore, especially walkers with dogs, caused most of the disturbance at Bridge Wood and Pond Ooze (and joggers at the latter, Table 3). Baitdiggers were large components of the disturbance at Nacton, Thorpe Bay and Erwarton Bay, and vehicles on the shore at Bradfield Bay and boats at Bridge Wood (Table 3). Otherwise, a range of activities caused disturbance at most sites.

3.2 Activities & disturbance Events People on the shore or seawall accounted for the majority of events that were recorded on the estuaries (64%), and those walking with or without dogs accounted for over half of all events (55%, 3 per hour per 500m Table 4). Motor vessels (16%, 0.9 per hour), sailing vessels (7%, 0.4 per hour) and vehicles on nearby roads and on the foreshore (8%, 0.4 per hour, primarily at Pin Mill) composed most of the remaining activity. Baitdiggers were relatively scarce (2% of events) and raptors (peregrines and sparrowhawks plus crows and great black-backed gulls) only occurred 13 times overall in 540 hours.

Disturbance events Overall, activities caused disturbance on 19% of occasions, consisting of minor disruption to birds on 8% of occasions (0.4 times per hour), local displacement of birds (6% or 0.3 times per hour) or departure of birds from the study area (5% or 0.3 times per hour). The total amount of disturbance caused to birds by the individual categories of activity was in direct proportion to their occurrence (rs = 0.8, n = 13, p = 0.001, Table 4). Most disturbance events were caused by people on the shore or seawall (65%, 0.7 per hour), mostly by walkers or those with dogs (55%, 0.6 per hour), but those with dogs caused a greater proportion compared with walkers alone (21% walkers, 34% walkers with dogs). Motor vessels also caused disturbance in direct proportion to their occurrence (16%), but sailing vessels and vehicles rarely caused disturbance (3% and 2% respectively). Scarce events such as shots, raptors and other activities (mainly loud, unspecified noises) usually caused disturbance to birds. There were also 61 dreads recorded (0.1 per hour overall). Season There was no change in the numbers events through the winter (H = 2.0, n = 180, ns, fig. 4), nor any evidence overall that birds responded more to activities in any particular month (H = 3.8, n = 180, ns, fig. 4), but large variation was imposed by data from different sites (and sample sizes were not large enough to investigate this on a site basis). Tide Overall, there were 1258 events at high tide and 1068 at low tide over the three winters, equating to identical rates of 5.2 per hr per site at both states of tide. Events at high tide were more than twice as likely to cause disturbance than those at low tide (fig. 5: H = 12.9., n = 180, p = 0.005). Birds feeding on rising tides were also sensitive, whereas those feeding on falling tides showed a similar response to those at low tide.

The frequencies of different activities at high and low tides were also similar with the exception of baitdiggers that occurred only at low tide (Table 5). Walkers, those with dogs, and passing vessels accounted for most of the events during counts at both states of tides (72% at high tide and 68% at low tide). The amount of disturbance caused to birds by different categories of activity was in direct proportion to their

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frequency at both states of tide (high tide rs = 0.7, n = 11, p = 0.01; low tide rs = 0.7, n = 12, p = 0.02). But activities on the upper shore (walkers, dog walkers, other people, cyclists, joggers etc) accounted for 80% of all disturbance at high tide and only 46% at low tide (Table 5 & fig. 6). Events on the lower shore and channel caused 44% of all disturbance at low tide compared with 14% at high tide (primarily owing to the added presence of baitdiggers, although motor vessels caused twice as much disturbance at low tide (26%) compared with high tide (12%, fig. 6)). Excluding data from raptors and shooting that have high impacts on birds regardless of state of tide, birds were most sensitive to cyclists and joggers and least sensitive to motor and sailing vessels at high tide (H = 90.9, n = 1259, p<0.0001) (sailing vessels and motor vehicles caused virtually no disturbance at either state of tide). At low tide, birds were most sensitive to baitdiggers (and least to cyclists and joggers: H = 74.4, n = 1052, p<0.0001).

3.3 Principal activities

Walkers and dogs Dog walkers were usually on their own (58%) or in pairs (33%) (mean number of people 1.6±0.1, n events = 606) and most were accompanied by one (67%) or two dogs (27%) (mean number of dogs 1.4±0.1, n events = 607). The largest group of dogs recorded was six and the largest combination recorded was 16 people with three dogs. Walkers without dogs were usually in groups: 41% were alone, 42% in pairs and 17% in larger groups of three or more (mean 2.0±0.1, n events = 640: the largest group recorded was 28). The effects on birds of both groups were greater at high tide than at low tide (walkers U = 54412, n = 641, p = 0.007; walkers with dogs U = 35283, n = 597, p<0.0001). Birds responded similarly to the groups at low tide (fig. 7: U = 34596, n = 530, ns) but walkers with dogs caused twice as much disturbance to birds at high tide (fig. 7: U = 54915, n = 708, p = 0.0001). Most dogs were not on leads (82%) and, although the mean disturbance caused by walkers with these was double that caused by walkers with dogs on leads (at both high and low tide), these effects were highly variable and differences were not significant (high tide: mean d off leads 0.6±0.1, n = 288; on leads 0.3±0.1, n = 60, U = 7609, ns; low tide: off leads 0.2±0.1, n = 210; on leads 0.1±0.1, n = 51, U = 5101, ns). Party size Party size had no effect on birds. Single dogs, pairs and groups of three or more caused the same amount of disturbance (high tide H = 1.4, n = 347, ns; low tide H = 2.0, n = 260, ns, fig. 8), even if they were off leads (high tide H = 0.74, n = 288, ns; low tide H = 1.6, n = 210, ns). Similarly, larger groups of walkers did not cause more disturbance than smaller groups (high tide H = 0.2, n = 360, ns; low tide H = 2.1, n = 280, ns). Nor did larger parties of baitdiggers have any effect (H = 5.1, n = 60, ns). Motor vessels A variety of vessels was recorded: small inflatables; motoring yachts; speedboats; barges; dredgers; customs and fishing vessels; and container ships. The most frequent were medium sized vessels (motor boats, dredgers, launches, fishing boats and other similar vessels) that accounted for 54% of motor vessel events. The remainder was composed of large container ships (28%), motoring yachts (12%) and speedboats (6%). Medium-sized boats caused 49% of the disturbance caused by motor vessels, large ships caused 24%, motoring yachts 7% and speedboats 10%.

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There was no difference in the occurrence of different vessels at high and low tide (ships 0.8 per count at high tide, 0.7 at low tide; medium motor boats 1.3 at high, 1.5 at low; yachts 0.3 per count at both tides; and speedboats 0.1 per count at both). But there were large differences in the responses of birds to the groups of vessels at different states of tide. At low tide, ships caused large amounts of disturbance compared with other groups (fig. 9: H = 18.0, n = 176, p = 0.0004) – 44% of ships caused disturbance compared with 15% of motorboats, 13% of powerboats and 10% of yachts. At high tide, speedboats had a disproportionate effect on birds (H = 16.7, n = 212, p = 0.0008), causing disturbance on 50% of occasions, compared with 17% of motorboats, 11% of yachts and just 6% of ships.

3.4 Factors affecting birds

Distribution of activity Overall, the response of birds to activities was greater on the Stour (i.e. they were more sensitive or easily disturbed: Orwell mean d = 0.32±0.01, n = 2560; Stour mean d = 0.64±0.06, n = 329; U = 491381, p<0.0001). There was a general pattern of insensitivity of birds in the middle and lower parts of the Orwell (fig. 10) and the response of birds was lowest at Nacton, Pin Mill and Shotley on the Orwell and greatest at Bradfield Bay and Erwarton Bay on the Stour and (H = 309.9, n = 2889, p<0.0001). The numbers of birds disturbed per event was greatest at Jacques Bay (mean 541±147) and Holbrook Bay (mean 521±136) on the Stour and the smallest at Bridge Wood (20±3) and Crane’s Hill (58±13) on the Orwell and Bradfield Bay on the Stour (39±6) (H = 119, n = 535, p<0.0001). Flocks of disturbed birds at other sites were in the range of 100-300 birds per event. Frequency of activities Activities that occurred relatively infrequently caused disturbance more easily (rs = -0.8, n = 13, p = 0.001, fig. 11). The mean response of birds to all category events was greatest to raptors, shooting and ‘other’ (usually loud noises), high in response to baitdiggers and aircraft and relatively low to remaining categories, especially vehicles and sailing vessels that caused very little disturbance overall (H = 224, n = 2889, p<0.0001, Table 4). Infrequent events also caused greater disruption to disturbed birds, and shots, baitdiggers and aircraft usually caused local or total displacement of birds (H = 29, n = 553, p = 0.004, Table 4) and also disturbed larger numbers of birds (fig. 12, H = 28.1, n = 535, p = 0.005).

Intensity of site activity

There was also a strong negative relationship between the response of birds and the overall level of activity at sites, and birds were less sensitive at more busy sites (fig. 13: rs = -0.68, n = 18, p = 0.002). This relationship was apparent for most activities (fig. 14: walkers rs= -0.79, n = 18, p<0.0001; sailing vessels rs = -0.77, n =12, p = 0.003; motoring vessels rs = -0.68, n = 17, p = 0.003; aircraft rs = -0.71, n = 9, p = 0.03; baitdiggers rs = -0.81, n = 6, p = 0.05). The disturbance caused to birds by some categories at sites was actually less where these events were more frequent (e.g. sailing vessels caused no disturbance whatsoever where there were more than 15 craft per winter, fig. 14). However, there was not a similar decline in bird sensitivity with increasing site use by dog walkers (rs = -0.38 n = 18, ns), caused primarily by a high sensitivity of birds at Bridge Wood to this activity (fig. 14: without this site, there was a significant decline in bird sensitivity – rs = -0.62, n = 17, p = 0.008).

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Numbers of birds The number of birds present during all counts was not related to the frequency of disturbance (rs = -0.04, n = 180, ns); nor were numbers at either high tide (rs = 0.01, n = 81, ns) or low tide (rs = -0.05, n = 68, ns) related to rates of disturbance. But fewer birds occurred during counts when there was more activity, regardless of whether this caused disturbance to birds (fig. 15: rs = -0.23, n = 180, p = 0.002). The relationship was strong at high tide (rs = -0.35, n = 81, p = 0.001), especially with the primary activities that caused disturbance at high tide (shore-based activities - walkers, walkers with dogs, cyclists, joggers, vehicles etc) and lower numbers of birds occurred where there were higher numbers of these (rs = -0.32, n = 81, p = 0.004). There was no similar relationship between the level of activity and the number of birds on mudflats at low tide (rs = -0.16, n = 68, ns) (or between the densities of birds per ha and activity: rs = 0, n = 68, ns). Nor was there any indication that lower numbers occurred when motorboat activities were greater (rs = -0.08, n = 68, ns).

Mudflat characteristics

Birds on narrower mudflats were not disturbed more (rs = 0.16, n = 18, ns), but there were lower densities of birds on narrower mudflats (rs = 0.47, n = 18, p = 0.05) and generally more activities at low tide on sections with narrow mudflats (rs = -0.49, n = 18, p = 0.04).

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4. DISCUSSION 4.1 Distribution of events

The sites selected represented a cross-section of the level and type of activity on both estuaries, as they included areas adjacent to urban areas, villages and marinas as well as a selection of remaining remote parts. Overall, a quarter of the Orwell was sampled, and this contained the majority of the primary access areas located along the estuary. With the exception of the more isolated area midway between the sites at Nacton and Bridge Wood (Mulberry Middle), visitor levels along much of the length of the northern shore are likely to be similar to the sample sites. On the southern shore, the busy areas either side of the Orwell Bridge and more isolated areas immediately below Pin Mill were not sampled. The study sites on the Stour were also a good representation of the general activity on the estuary. Access and visitor pressure on the northern shore is probably fairly similar along much of its length, with the exception of busier areas at Shotley. On the southern shore, busier areas at Manningtree, Wrabness and Harwich were not sampled but nor was the large shoreline in the RSPB reserve at Copperas Bay with restricted access. Some areas that were close to villages were popular with walkers (Pin Mill, Levington, Shotley and Erwarton Bay), but the busiest sites were those around Orwell Country Park where specific car parks are provided (Pond Ooze, Bridge Wood and Nacton) and that are within easy reach of the resident population of Ipswich. As might be expected, the quietest areas were those that were least accessible by roads and paths – Freston on the southern side of the Orwell and Stutton on the northern shore of the Stour. Ease of access was the key aspect. Very low activity was recorded at Alnesbourne, despite it being immediately adjacent to one of the busiest sites at Bridge Wood, owing to the relative difficulty of crossing a small muddy area between the two sites. The majority of boat traffic during the winter appeared to be commercial and travelling between Felixstowe and Ipswich. There were indications that there were more craft in the lower parts of the estuaries at low tide and that activity around the top of the Orwell occurred primarily at high tide. There was very little traffic on the Stour.

4.2 Rates of disturbance The Orwell is a busy estuary in winter compared with the Stour. For every 500m section of the estuaries, an event occurred every 9 minutes on the Orwell and one every 30 minutes on the Stour (6.5 and 1.9 events per hour). Extrapolation of these frequencies to the entire estuaries suggests that there were about 360 events every hour on the Orwell as a whole, and about 118 every hour on the Stour2. The rates with which wintering birds were disturbed on the two estuaries (1.1 and 0.7 per hour per 500m on the Orwell and Stour respectively) suggests that there were 55 separate disturbance events every hour on the Orwell and 44 every hour on the Stour. Disturbance frequencies in other studies are quoted for specific flocks of birds, rather than for study areas, but available data are broadly similar to those recorded in the SPA: e.g. 1.4 per hour for staging geese (Belanger & Bedárd 1989); 1.7 per hr for waders on a beach (Fitzpatrick & Bouchez 1998); 0.4 per hr for geese in fields (Gill et al 1996); 0.7 per hr for ducks at roost (Keller 1988); and 0.7 per hr for coastal geese (Owens 1977). But two studies also give an indication of background activity: around 50 walkers per hour to a beach usually caused less than 1 disturbance per hour (or about one in 50 events caused disturbance, Kirby et al 1993); and a busy area of

2 This extrapolation should be treated with caution, as many events would traverse more than one section, such as boats or walkers.

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saltmarsh in Holland used by up to 200 people at a time caused disturbance rates of 0.2-6.9 per hour (or one in 30 or more events caused disturbance, Stock 1993). These suggest that birds on the SPA, and in particular the Stour, are relatively sensitive to activity as about one in six events on the Orwell and one in three on the Stour caused disturbance.

4.3 Activities and disturbance Walkers and those with dogs were the most frequent events and caused the greatest proportion of the disturbance recorded on the estuaries, but the majority caused no disturbance at all. Every walker displaced 24 birds on average, every dog walker 33 birds, and every other activity on the shore 30-50 birds per event. On the water, every motor vessel disturbed 21 birds and every sailing vessel only 4 birds. Uncommon events had much bigger effects and disturbed more birds e.g. on average every aircraft disturbed 150 birds, every baitdigger 159 and every shot 340 birds. Despite concern about the effects of dogs on wildlife (Taylor 2005, Banks & Bryant 2007) and on the Orwell (Wright 2007), there was no difference at low tide between the effects of walkers and walkers with dogs when birds were a long way from the foreshore to which people and dogs were more or less confined. But at high tide, walkers with dogs caused much more disturbance, presumably owing to the proximity of roosting birds to access routes. The effect on birds of dogs off leads was also twice as great as those on leads, but the sample size of dogs on leads was so small that the difference was not significant statistically. Furthermore, observers were not asked to distinguish whether dogs off leads were under close control. They did record, however, that running dogs often caused disturbance, as did shouted encouragement, admonishment and other activities by owners (such as throwing sticks). Dogs off leads can cause problems to birds elsewhere, although this is associated primarily with disruption to breeding birds close to footpaths (Yalden & Yalden 1990, Taylor et al 2005, Langston et al 2007), but recent work has shown that bird numbers may be reduced even if a dog is kept on a lead (Banks & Bryant 2007). Observers frequently reported that loud noises and fast-moving objects had a disproportionate influence on birds. Fast-moving objects or unpredictable activities are consistent causes of disturbance in other studies (Burger 1981, Fitzpatrick & Bouchez 1998, Smit & Visser 1993). Helicopters and other low-flying or noisy aircraft usually caused general panic among birds. For the combined reasons of speed and noise, powerboats caused relatively large amounts of disturbance, the latter probably because their shallow draft allowed them close access to the shore at high tide (when they were most disruptive). Most disturbance caused by boats, however, came from ships and container vessels at low tide and observers usually reported that it was the wash hitting mudflats that caused disruption, rather than the passing of the vessel itself. Otherwise, slow-moving and quiet objects, such as sailing boats on the water or horses on the foreshore, caused very little disturbance.

4.4 Effects of landscape Foraging and roosting areas are partly selected to reduce predation risk (Whitfield 1985, Rehfisch et al 2003) and birds avoid obstructions that may hide predators (Madsen 1985). At Bridge Wood, birds were highly sensitive to a range of activities, but especially dogs, and the rates of disturbance were the highest in the SPA, along with the adjacent site, Pond Ooze. Both of these sites have paths along the shore

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that are shielded for the most part by woodland and that emerge suddenly onto the foreshore. It seems probable that birds were intrinsically nervous, and this surprise element was an important factor in the response of birds throughout the study

Mudflat width was also an important factor affecting the numbers of birds at sites, probably for the same reasons of predator avoidance. Birds may avoid narrow mudflats and perhaps especially those close to seawalls. It also seems likely that high activity levels have a disproportionate effect on the presence of birds on narrow mudflats. The mean densities of birds on the identical and adjacent mudflats at Crane’s Hill and Shotley Point (both 125m wide) were three times greater at the former (Crane’s Hill 36 birds per ha; Shotley Point 12 per ha) whilst activity levels were three times greater at the latter (Crane’s Hill 11 events per count, Shotley Point 36 per count).

At low tide, therefore, there were low rates of disturbance of birds on many mudflats below 200m wide, as few birds were present. Birds on mudflats over 500m, such as Nacton and Alnesbourne on the Orwell and most sites on the Stour, appeared largely unaffected by activity on the shore and disturbance rates on these were also low. Generally, the highest disturbance rates were recorded from mudflats of 250-400m where both bird numbers and activity levels were high, such as at Bridge Wood and Pond Ooze on the Orwell.

Birds feeding at sites with wide mudflats were vulnerable to disturbance at half-tides. Most disturbance events at Nacton occurred on rising tides (12 out of 23), when the distance between the remaining feeding area on the mudflat and the shore was reducing. Large numbers of birds that have gathered in pre-roosts or to feed on remaining exposed areas of mudflats may be especially vulnerable to disturbance at these times (some of the largest disturbance events took place at this state of tide and the mean number disturbed at Nacton on rising tides was 479, at Levington 623 and Holbrook Bay 625, compared with 280, 151 and 298 at other states of tides respectively). The northern shore of the Orwell is particularly important for top-tide feeding (Wright 2007).

4.5 Habituation

The true effect of disturbance was probably under-estimated by the method of counting whereby large, unseen disruption before a count or disturbance early in its progress may have reduced numbers or altered the reaction of remaining birds for the rest of the count. For example, a baitdigger present on the mudflat at the beginning of the count may have displaced sensitive birds already and his continued activity may have elicited no further response in remaining birds and therefore be recorded as having little effect. As in other coastal areas (Koolhaas et al 1993, Smit & Visser 1993), birds clearly habituated to some activities, such as sailing vessels and vehicles (unless they were on the shore, as at Bradfield Bay, or on seawalls, as at Levington), as there was little or no response from birds at sites where both birds and these activities were frequent. Sailing boats caused absolutely no disturbance where they were most frequent e.g. at Thorpe Bay (where there were large numbers of birds at low tide), but they did at sites were these events were scarce (Gill et al 2001b noted an absence of any effects of activities close to marinas in East Anglian estuaries). Vehicles accessing the public house and public road on the foreshore at Pin Mill also rarely caused disturbance but they did elsewhere where they were infrequent (Klein et al 1995 also noted a habituation to moving vehicles).

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However, the overall relationship between bird numbers and activity levels at sites in the SPA shows clearly that fewer birds occurred at busier sites, especially at high tide, and disturbance rates were lower where there were fewer birds e.g. on narrow mudflats. It is reasonable to assume that these birds are: a) tolerant species or individuals; b) in the furthest part of the mudflat or the least accessible part of saltmarsh; c) spread more thinly over the site. For example, very few walkers and dogs caused disturbance at high tide at Nacton, even though it was the busiest site, but there were very few birds present. Smaller flocks of birds are more tolerant of potential sources of disturbance (Owens 1977, Smit & Visser 1993). Activities also caused hardly any disturbance on the narrow mudflat at Shotley at low tide for the same reason. The observer at this busy site frequently recorded the comment “no birds to disturb” alongside records of walkers on the seawall. Generally, fewer birds are present when people are as well (Burger 1981, Burton et al 2002b). Therefore, most apparent habituation of birds in the SPA may just be the result of fewer numbers of birds.

4.6 Other effects of disturbance

Two other questions were asked of the data, but these were difficult to answer owing to: a) variations in the numbers of birds at different sites; and b) the manner in which counts were undertaken (counts of birds disturbed did not record those that were not disturbed): 1) Whether particular species were more sensitive to activity? 2) Whether bird numbers recover after disturbance at a site and if so, how long do they take?

A comparison of the relative frequencies with which species occurred during background counts and in disturbance counts suggests that particular species were sensitive to activities. Redshank were most easily disturbed at high tide and least affected were black-tailed godwit and golden plover (Table 6). At low tide, redshank and brent geese were most easily disturbed. Generally though, the level of disturbance to any particular species was a function of its occurrence, and more widespread species were disturbed more often (high tide rs = 0.97, n = 15, p<0.0001; low tide rs = 0.84, n = 15, p<0.0001). Relatively small numbers of most species were involved in disturbance events, with the exception of some species that occur primarily in flocks e.g. knot and dunlin (Table 6). However, these represented relatively large proportions of the SPA populations of some species e.g. each event at high tide disturbed 4-5% of the SPA population of brent goose, dunlin, lapwing and turnstone, 7% of knot and oystercatchers and 8% of black-tailed godwit. At low tide, each event disturbed less than 4% of the population of most species, but 5-7% of oystercatchers, redshank and pintail. These proportions will be greater on the Orwell alone owing to the smaller populations present.

Attempts were made to investigate the recovery of bird numbers after disturbance, but owing to the variations in numbers and responses of birds at sites, this has to be examined site by site. Most counts were undertaken at Freston, where 30 counts took place over the three winters, but even these did not provide enough data at both states of tide. Presumably, recovery of numbers after disturbance will depend on the level of activity continuing in a given area – and numbers will remain low where activity remains high. Belanger & Bedárd (1989) found that numbers of geese remained low for a day or so after disturbance, but constant disturbance may reduce numbers for longer (Burton 2002b). It is interesting to note that although there was a

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strong relationship between bird numbers and activity levels during counts at sites, there was no relationship between the mean winter numbers of birds at sites and overall activity level (rs = -0.19, n =18, ns). This suggests that activities may not be having a permanent effect on bird numbers at current levels of disturbance.

4.7 The potential impacts on bird populations of the SPA High tide Shelter, risk of predation, proximity to feeding grounds and the absence of disturbance are key aspects of the selection by birds of areas in which to roost (Rehfisch et al 2003). Therefore, birds are highly faithful to particular roost sites (Rehfisch et al 1996). Frequent disturbance has been shown to cause the abandonment of roosts, causing birds to re-locate to other sites or other estuaries (Mitchell et al 1988, Rehfisch et al 2003). Loss of roosting sites may result in either a decline in usage of feeding grounds, or large energetic costs if they continue to use traditional feeding grounds (Mitchell et al 1988, Rehfisch et al 2003). Low tide The selection of areas in which to feed at low tide is driven primarily by the density of prey (Goss-Custard 1977, Bryant 1979), and to a lesser extent the risk of predation (Whitfield 1985, Cresswell 1994). In areas or periods of high prey availability, occasional disturbance probably impacts little on birds, even if they are displaced regularly (Goss-Custard et al 2006). Birds may even be more readily disturbed if they can re-locate to alternative areas (Gill 2001a) or if they are in better condition (Beale & Monaghan 2004b). Therefore, high disturbance rates do not always reflect an impact on birds (Gill 2001a, Stillman & Goss-Custard 2002), but low disturbance rates can be damaging when birds have no alternatives and especially when food resources are scarce (Goss-Custard et al 2006). Regardless of impact, reduced numbers usually occur as a result of disturbance: either temporarily (Belanger & Bedárd 1989) or permanently (Burton 2002b, c). Stour Activity levels were low on the Stour, there were more birds in this estuary and these were more easily disturbed than those on the Orwell. Greater numbers were also disturbed, and once disturbed they were more prone to leave the study area than birds on the Orwell (high tide H = 50.7, n = 1288, p<0.0001; low tide H = 9.3, n = 156, p = 0.002). The behaviour of birds on the Stour (the ready response of birds in a relatively quiet and large estuary) suggests that birds are moving to alternative areas in response to disturbance, especially on the expansive mudflats at low tide. Therefore, the relatively small amount of disturbance on this estuary is unlikely to be affecting bird populations. Their behaviour may be a reflection of the large numbers present (as this will increase the likelihood of some birds reacting, Owens 1977). Orwell There are greater numbers of birds on the Orwell at high tide than at low tide (Armitage et al 2003). Furthermore, the numbers recorded roosting at the disturbance study sites were consistently lower than those feeding. There were also fewer birds where there was more activity. The only large roosts were at sites with few visitors (Freston) or where birds were relatively isolated e.g. on saltmarsh at Levington. This indicates that activities at high tide are reducing the availability of roosting sites on the Orwell (large numbers of birds that feed here are known to roost on the Stour). Birds were less affected by activities at low tide, but they were vulnerable to repeated disturbance on medium-sized mudflats and smaller numbers used narrow mudflats. The low displacement of birds remaining in these areas indicates that they were

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reluctant to leave areas in response to disturbance. Furthermore, the relatively high activity levels around most of the estuary, as well as relatively narrow mudflats, suggest that there may be few suitable alternative areas available for birds in this estuary. The medium-sized mudflats of the upper reaches of the Orwell around Bridge Wood are traditionally the most important feeding grounds for birds in the estuary and are also where recent declines in birds have been most pronounced (Armitage et al 2003). Birds attempting to feed at these sites must tolerate repeated interruptions and these are likely to be having an impact on feeding efficiency. Although there has always been the facility for public access to this shore, large numbers of visitors are more recent, especially with the improvements in access – since the development of the area as a Country Park in the mid 1990s. The neighbouring mudflat in front of Piper’s Vale is the only part of the Orwell estuary to which there is no access to the shore. This supports the highest density of feeding birds on the Orwell (Wright 2001).

4.8 Conclusions

1. Shore activities, in particular people and those with dogs, caused most of the disturbance recorded in the SPA, but usually displaced small numbers of birds. 2. The most disruptive events were relatively scarce, usually baitdiggers, aircraft and shots. 3. Fast, sudden movement and loud noises were the primary stimuli that disturbed birds. 4. Activities at high tide caused twice as much disturbance than those at low tide. 5. The susceptibility of birds to disturbance was accentuated on narrow mudflats and by shorelines that hid the approach of activities.

6. Habituation was an effect of reduced numbers of birds. 7. Fewer birds occurred where levels of activity, not disturbance, were greater.

8. The levels of activity around the Orwell at high tide and the lack of alternative feeding areas at low tide suggest that disturbance may be having an impact on bird populations of this estuary.

9. Activity rates were relatively low on the Stour and the wide mudflats and absence of boat traffic on the channel reduced the effects of activities further at low tide. The behaviour of birds suggests that they may be impacted little by disturbance. 10. But any increase in shore activities on the Stour will increase the disturbance of important roosts that serve both the Stour and birds displaced from the Orwell.

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5. Acknowledgements Our thanks are extended to the dedicated team of counters of the Orwell and Stour who undertook the fieldwork for the project: Robin Biddle, R. Devonshire, John Glazebrook, Bill Last, Eddie Marsh, Nick Mason, Nigel Odin, Rod Plowman, Pearson Silburn, John Thirlwell and John Turner. Fieldwork was funded by Natural England and the Suffolk Coast and Heaths Unit. The report was funded by Natural England, the RSPB, Suffolk Coasts and Heaths Unit and The Green Blue (a joint BMF and RYA initiative).

Our thanks also for advice and support to the British Trust for Ornithology and the Suffolk Wildlife Trust and to Lynn Wright for data entry.

6. REFERENCES

Anderson, D.W. & Keith, J.D. 1980. The human influence on seabird breeding success: conservation implications. Biological Conservation, 18, 65-80.

Armitage, M.J.S. & Rehfisch, M.M. (2002a) Assessing Waterbird Population trends on the Stour and Orwell Estuaries SPA. BTO Research Report 297. Thetford.

Armitage, M.J.S., Austin, G.E., Ravenscroft, N.O.M. & Rehfisch, M.M. 2003. Towards determining the causes of declines in waterbird numbers on the Stour and Orwell estuaries SPA. BTO Research Report No. 338 (report to Posford Haskoning Ltd).

Atkinson, P.W., Baker, A.J., Bennett, K.A., Clark, N.A., Clark, J.A., Cole, K.B., Dekinga, A., Dey, A., Gillings, S., Gonzalez, P.M., Kalasz, K., Minton, C.D.T., Newton, J., Niles, L.J., Piersma, T., Robinson, R.A. & Sitters, H.P. 2007. Rates of mass gain and energy deposition in red knot on their final spring staging site is both time- and condition-dependent. Journal of Applied Ecology, 44, 88-895.

Austin, G. & Rehfisch, M.M. 2005. Shifting non-breeding distribution of migratory fauna in relation to climatic change. Global Change Biology, 11, 31-38.

Banks, A.N., Collier, M.P., Austin, G.E., Hearn, R.D. & Musgrove, A.J. 2006. Waterbirds in the UK 2004/05: The Wetland Bird Survey. BTO/WWT/RSPB/JNCC, Thetford.

Banks, P.B. & Bryant, J.V. 2007. Four-legged friend or foe? Dog walking displaces native birds from natural areas. Biology Letters: www.journals.royalsoc.ac.uk/ content/y142043307645mj2.

Beale, C.M. & Monaghan, P. 2004a. Human disturbance: people as predation-free predators? Journal of Applied Ecology, 41, 335-343.

Beale, C.M. & Monaghan, P. 2004b. Behavioural responses to human disturbance: a matter of choice? Animal Behaviour, 68, 1065-1069.

Belanger, L. & Bedárd, J. 1989. Responses of staging Greater Snow Geese to human disturbance. Journal of Wildlife Management, 53, 713-719.

Belanger, L. & Bedárd, J. 1990. Energetic cost of man-induced disturbance to staging Snow Geese. Journal of Wildlife Management, 54, 36-41.

Bolduc, F. & Guillemette, M. 2003. Human disturbance and nesting success of Common Eiders: interaction between visitors and gulls. Biological Conservation, 110, 77-83.

Bryant, D.M. 1979. Effects of prey density and site character on estuary usage by overwintering waders (Charadrii). Estuarine and Coastal Marine Science, 9, 369-384.

Burger, J. 1981. The effect of human activity on birds at a coastal bay. Biological Conservation, 21, 231-241.

Burton, N.H.K., Paipai, E., Armitage, M.J.S., Maskell, J.M., Jones, E.T., Struve, J., Hutchings, C.J. & Rehfisch, M.M. 2002a. Effects of reductions in organic and

25

nutrient loading on bird populations in estuaries and coastal waters of England and Wales. Phase 1 report. BTO Research Report 267, Thetford.

Burton, N.H.K., Armitage, M.J.S., Musgrove, A.J. & Rehfisch, M.M. 2002b. Impacts of man-made landscape features on numbers of estuarine waterbirds at low tide. Environmental Management, 30, 857-864.

Burton, N.H.K., Rehfisch, M.M. & Clark, N.A. 2002c. Impacts of disturbance from construction work on the densities and feeding behaviour of waterbirds using the intertidal mudflats of Cardiff Bay, UK. Environmental Management, 30, 865-871.

Burton, N.H.K., Rehfisch, M.M., Clark, N.A. & Dodd, S.G. 2006. Impacts of sudden winter habitat loss on the body condition and survival of redshank Tringa totanus. Journal of Applied Ecology, 43, 464-473.

Cayford, J. 1993. Wader disturbance: a theoretical review. Wader Study Group Bulletin, 68, 3-5.

Cooper, N., Skrzypczak, T. & Burd, F. 2000. Erosion of the saltmarshes of Essex between 1988 and 1998. Report to the Environment Agency.

Cresswell, W. 1994. Age-dependent choice of redshank (Tringa totanus) feeding location: profitability or risk? Journal of Applied Ecology, 63, 589-600.

Davidson, N.C.& Rothwell, P.I. 1993. Human disturbance to waterfowl on estuaries: conservation and coastal management implications of current knowledge. Wader Study Group Bulletin, 68, 97-105.

Erwin, R.M. 1980. Breeding habitat use by colonially nesting waterbirds in two mid-Atlantic US regions under different regime of human disturbance. Biological Conservation, 18, 39-51.

Fitzpatrick, S. & Bouchez, B. 1998. Effects of recreational disturbance on the foraging behaviour of waders on a rocky beach. Bird Study, 45, 157-171.

Fox, A.D., Bell, D.V. & Mudge, G.P. 1993. A preliminary study of the effects of disturbance on feeding wigeon grazing on eel-grass Zostera. Wader Study Group Bulletin, 68, 67-71.

Gill, J.A., Sutherland,W.J. & Watkinson, A.R. 1996. A method to quantify the effects of human disturbance on animal populations. Journal of Applied Ecology, 33, 786-792..

Gill, J.A., Norris, K. & Sutherland, W.J. 2001a. Why behavioural responses may not reflect the population consequences of human disturbance. Biological Conservation, 97, 265-268.

Gill, J.A., Norris, K. & Sutherland, W.J. 2001b. The effects of disturbance on habitat use by black-tailed godwits Limosa limosa. Journal of Applied Ecology, 38, 846-856.

Goss-Custard, J.C. & Durrell, S.E.A. le V. dit 1990. Bird behaviour and environmental planning: approaches in the study of wader populations. Ibis, 132, 273-289.

Goss-Custard, J.D. & Verboven, N. 1993. Disturbance and feeding shorebirds on the Exe estuary. Wader Study Group Bulletin, 68, 59-66.

Goss-Custard, J.D., Jones, R.E. & Newberry, P.E. 1977. The ecology of the Wash. I. Distribution and diet of wading birds (Charadrii). Journal of Applied Ecology, 14, 681-700.

Goss-Custard, J.D., Clarke, R.T., Durell, S.E.A. le V. dit, Caldow, R.W.G. & Ens, B.J. 1995. Population consequences of winter habitat loss in a migratory shorebird. II. Model predictions. Journal of Applied Ecology, 32, 337-351.

Goss-Custard, J.D., Triplet, P. Sueur, F. & West, A.D. 2006. Critical thresholds of disturbance by people and raptors in foraging birds. Biological Conservation, 127, 88-97.

Hill, D., Hockin, D., Price, D., Tucker, G., Morris, R. & Treweek, J. 1997. Bird disturbance:improving the quality and utility of disturbance research. Journal of Applied Ecology, 34, 275-288.

JNCC 2001. Stour and Orwell Estuaries SPA citation. www.jncc.gov.uk.

26

Keller, V.E. 1988. Human disturbance of eider crèches on the Ythan estuary. Nature Conservancy Council.

Kirby, J.S., Clee, C. & Seager, V. 1993. Impact and extent of recreational disturbance to wader roosts on the Dee estuary: some preliminary analysis. Wader Study Group Bulletin, 68, 53-58.

Klein, M.L., Humphrey, S.R. & Percival, H.F. 1995. Effects of ecotourism on the distribution of waterbirds in a wildlife refuge. Conservation Biology, 9, 1454-1465.

Koolhaas, A., Dekinga, A. & Piersma, T. 1993. Disturbance of foraging knots by aircraft in the Dutch Wadden Sea in August-October 1992. Wader Study Group Bulletin, 68, 20-22.

Langston, R.H.W., Liley, D., Murison, G., Woodfield, E. & Clarke, R.T. 2007. What effects do walkers and their dogs have on the distribution and productivity of breeding European Nightjar Caprimulgus europaeus. Ibis, 149 (Suppl. 1), 27-36.

Madsen, J. 1985. Impact of disturbance on field utilisation of pink-footed geese in West Jutland, Denmark. Biological Conservation, 33, 53-63.

Madsen, J. 1995. Impacts of disturbance on migratory waterfowl. Ibis, 137 (Supplement), S67-S74.

Madsen, J. 1998a. Experimental refuges for migratory waterfowl in Danish wetlands. I. Baseline assessment of the disturbance effects of recreational activities. Journal of Applied Ecology, 35, 386-397.

Madsen, J. 1998b. Experimental refuges for migratory waterfowl in Danish wetlands. II. Tests of hunting disturbance effects. Journal of Applied Ecology, 35, 398-417.

Mitchell, J.R., Moser, M.E. & Kirby, J.S. 1988. Declines in midwinter counts of waders roosting on the Dee estuary. Bird Study, 35, 191-198.

Mooij, J. 1991. Numbers and distribution of grey geese (genus Anser) in the Federal Republic of Germany, with special reference to the lower Rhine region. Ardea 79, 143-158.

Musgrove, A.J., Langston, R.H.W., Baker, H. and Ward, R.M. (eds.) 2003. Estuarine Waterbirds at Low Tide: the WeBS Low Tide Counts 1992/93 to 1998/99. Wader Study Group/British Trust for Ornithology/Wetlands and Wildfowl Trust/Royal Society for the Protection of Birds/Joint Nature Conservation Committee, Thetford, 310pp.

Owen, M. 1993. The UK shooting disturbance project. Wader Study Group Bulletin, 68, 35-46.

Owens, N.W. 1977. Responses of wintering brent geese to human disturbance. Wildfowl, 28, 5-14.

Posford Duvivier Environment 1998. Harwich Haven Approach Channel Deepening. Appropriate Assessment. Report to Harwich Haven Authority.

Rehfisch, M.M., Clark, N.A., Lansgton, R.H.W. & Greenwoood, J.J.D. 1996. A guide to the provision of refuges for waders: an analysis of 30 years of ringing data from the Wash, England. Journal of Applied Ecology, 33, 673-687.

Rehfisch, M.M., Insley, H. & Swann, R. 2003. Fidelity of overwintering shorebirds to roosts on the Moray Basin, Scotland: implications for predicting impacts of habitat loss. Ardea, 91, 53-70.

Smart, J., and Gill, J.A. 2003. Non-intertidal habitat use by shorebirds: a reflection of inadequate intertidal resources? Biological Conservation, 111, 359-369.

Smit, C. & Visser, G.J.M. 1993. Effects of disturbance on shorebirds: a summary of existing knowledge from the Dutch Wadden Sea and Delta area. Wader Study Group Bulletin, 68, 6-19.

Stillman, R.A. & Goss-Custard, J.D. 2002. Seasonal changes in the response of oystercatchers Haematopus ostralegus to human disturbance. Journal of Avian Biology, 33, 358-365.

27

Stillman, R.A., West, A.D., Caldow, R.W.G. & Durrell, S.E.A. le V. dit 2007. Predicting the effect of disturbance on coastal birds. Ibis, 149 (Suppl. 1), 9-14.

Stock, M. 1993. Studies on the effects of disturbances on staging brent geese: a progress report. Wader Study Group Bulletin, 68, 29-34.

Suffolk Wildlife Trust 2007. Ornithological Monitoring of the Stour and Orwell Estuaries Special Protection Area: Winters 1999/2000 to 2006/2007. Report to Harwich Haven Authority.

Swennen, C., Leopold, M.F. & Bruijn, L.L.M. de 1989. Time-stressed oystercatchers, Haematopus ostralegus, can increase their intake rate. Animal Behaviour, 38, 8-22.

Symonds, F.L. & Langslow, D.R. 1986. The distribution and local movements of shorebirds within the Moray Firth. Proceedings of the Royal Society Edinburgh, 91B, 143-168.

Taylor, K., Anderson, P., Taylor, R.P., Longden, K. & Fisher, P. 2005. Dogs, access and nature conservation. English Nature Research Report No. 649. English Nature, Peterborough.

Townshend, D.J. & O’Connor, D.A. 1993. Some effects of disturbance to waterfowl from bait-digging and wildfowling at Lindisfarne National nature Reserve, north-east England. Wader Study Group Bulletin, 68, 47-52.

Verhulst, S., Oosterbeek, K. Ens, B.J. 2001. Experimental evidence for effects of human disturbance on foraging and parental care in oystercatchers. Biological Conservation, 101, 375-380.

West, A.D., Goss-Custard, J.D., Stillman, R.A., Caldow, R.W.G., Durrell, S.E.A. le V. dit & McGrorty, S. 2002. Predicting the impacts of disturbance on shorebird mortality using a behaviour-based model. Biological Conservation, 106, 319-328.

Whitfield, D.P. 1985. Raptor predation on wintering waders in south-east Scotland. Ibis, 127, 544-558.

Wright M. T. 2001. Orwell Estuary – Systematic review of waterbirds. English Nature Research Report No. 381.

Wright, M. 2007. An overview of sensitive sites and assessment of recreational impacts on the Orwell estuary. Suffolk Wildlife Trust, Ashbocking.

Yalden, P.E. & Yalden, D.W. 1990. Recreational disturbance of breeding Golden Plovers Pluvialis apricarius. Biological Conservation, 51, 243-262.

Yates, M.G., Goss-Custard, J.D., McGrorty, S., Lakhani, K.H., Durrel, S.E.A. le V. dit, Clarke, R.T., Riggin, W.E., Moy, I., Yates, T., Plant & R.A. Frost, A.J. 1993. Sediment characteristics, invertebrate densities and shorebird densities on the inner banks of the Wash. Journal of Applied Ecology, 30, 599-614.

28

7. TABLES

29

Table 1: Features of the study sites on the Stour and Orwell estuaries in 2004/005 to 2006/07 (see maps in appendix 1). ORWELL Shoreline

extent m Shape of shore Mudflat width

m Features of upper shore Access/pressure points

Pond Ooze 500 Slightly convex 375 Open shore of sand/mud bordered by fields and trees.

Paths along shore from Country Park at Bridge Wood 1km to south-east and Piper’s Vale 500m to north-west. Path down to shore via field below Pond Hall Farm.

Freston 500 Straight 375 Mudflat bordered by open fields.

Paths down to shore via Freston Park and access to Freston Hard at northern end of section where there is a small boat club, but no public access along the shore.

Bridge Wood 500 Convex – slight point between two bays

250 Open sand/mud fringed by woodland

Paths through Bridge Wood (Orwell Country Park) to the shore from a car park 750m to the north and along the shore from Piper’s Vale (Orwell Country Park) 1.5km to the north-west.

Alnesbourne 500 Concave – west end of Mansbrook Bay

625 10-20m of raised saltmarsh between woodland and mudflat.

Section 500m east of access to shore from Bridge Wood. Path over saltmarsh bordering the shore from Bridge Wood to Mansbrook Grove.

Pin Mill 500 Straight 250 Narrow fringe of saltmarsh, otherwise field, woodland and garden.

Road to shore at hard by the Butt & Oyster public house and along shore 150m to north-west. Paths from road along field behind shore.

Nacton 500 Concave – slight bay in shoreline

550 Open sand/mud shore bordered by woodland and fields

Path from car park immediately above shore in centre of study section and routes along the upper shore in either direction.

Levington 500 Concave – incorporating lower reaches of creek.

250 Seawall with a narrow fringe of saltmarsh

Paths from Levington village 750m to north and Levington marina 500m to east. Concentration of activity at marina.

Thorpe Bay 750 Concave – deep bay

375 to 100 at south end.

Seawall between mudflat and reservoir (Loompit Lake) and Trimley Marshes.

Principally a path along seawall from Levington Marina 500m to west, but also a path down to shore from Trimley St Martin village 1km to east.

Crane’s Hill 1000 Concavity in seawall containing saltmarsh, otherwise straight, narrow mudflat

125 Seawall separating mudflat from grazing marsh.

Relatively remote – paths from Shotley marina and Shotley Gate village along seawall 2km to south and from Church End 1km to west across grazing marsh.

Shotley 1250 Straight, narrow shore and mudflat.

125 Seawall separating mudflat from grazing marsh.

Section incorporated paths around Shotley marina and from Shotley Gate village immediately to the west. Concentration of boat activity via marina.

30

Table 1 (continued): Features of the study sites on the Stour and Orwell estuaries in 2004/005 to 2006/07. STOUR Shoreline

extent m Shape of shore Mudflat width

m Features of upper shore Access/pressure points

Erwarton 500 Concave 500 Mudflat bordering field Path along field edge from Shotley Gate 1km to east and from Shotley village 1km to north.

Holbrook 500 Convex 1250 Seawall between fields and mudflat.

Path along seawall from car park 250m to north-west and from Lower Holbrook village 250m to north. Small concentration of moorings in Holbrook Creek.

Jacques Bay 1250

Slightly concave 750 Fringe of saltmarsh and shingle bordering woodland and fields.

Path and bridleway along foreshore from parking at Wrabness Local Nature Reserve to east and road to shore (Wall Lane) at eastern end of section.

Bradfield Bay 500 Slightly concave 875 Shingle foreshore fringing fields.

Bridleway behind foreshore and access road to shore from Bradfield village 500m to south.

Stutton 500 Slightly convex 250 Seawall around saltmarsh fringe.

Relatively remote – path along seawall through section.

31

Table 2: The counts undertaken at the study sites. Winter Site Estuary Month Tide Nov Dec Jan Feb Mar High Falling Low Rising 2004/05 Freston O 2 2 2 2 2 3 3 2 2 2004/05 Bridge Wood O 2 2 2 2 2 2 3 2 3 2004/05 Nacton O 2 2 2 2 2 4 1 2 3 2004/05 Levington O 1 3 3 3 3 3 2 2 2004/05 Erwarton S 2 2 2 2 2 3 2 2 3 2004/05 Holbrook S 1 1 3 2 3 2 3 2 3 2005/06 Freston O 2 2 2 2 2 5 5 2005/06 Alnesbourne O 2 2 2 2 2 5 5 2005/06 Levington O 2 2 2 2 2 5 5 2005/06 Thorpe Bay O 4 2 2 2 5 5 2005/06 Crane’s Hill O 2 1 3 2 2 8 2 2005/06 Shotley O 2 2 2 2 2 5 5 2006/07 Pond Ooze O 1 2 3 2 1 5 4 2006/07 Freston O 2 2 2 2 2 6 4 2006/07 Pin Mill O 2 2 2 2 2 5 5 2006/07 Jacques Bay S 2 2 2 2 2 5 5 2006/07 Thorpe Bay O 1 1 2006/07 Bradfield Bay S 2 2 2 2 2 5 5 2006/07 Stutton S 2 2 2 2 2 5 5 Total 31 35 40 37 37 81 15 68 16

32

Table 3: The frequencies (number per 500m per hour) of events (e) and events causing disturbance (de) at the study sites over all tides (* except baitdiggers for which rates are calculated using only low tides).

People Joggers Cyclists Walkers Walkers & dogs

Bait- diggers*

Vehicles Shooting Motor vessels

Sailing vessels

Aircraft Raptors

e de e de e de e de e de e de e de e de e de e de e de e de

Upper Orwell Pond Ooze - - 1.00 0.26 0.07 - 1.41 0.33 2.67 0.74 0.08 - - - - - 1.04 0.26 0.44 0.07 0.04 0.04 0.04 0.04 Bridge Wood 0.27 0.17 0.40 0.07 0.23 0.10 2.03 0.27 3.60 1.73 1.33 0.33 - - 0.07 - 2.03 0.80 0.50 0.17 0.10 0.03 0.07 0.07 Alnesbourne 0.03 - 0.10 0.03 0.10 0.07 0.80 0.20 0.47 0.20 - - 0.03 - - - 0.70 0.20 0.13 0.07 0.03 - - - Freston 0.27 0.07 0.03 0.01 0.01 - 0.33 0.16 0.33 0.12 0.03 - - - - - 0.20 0.06 0.03 0.01 - - - - Mid & lower Orwell Pin Mill 0.53 0.30 0.03 - 0.13 - 2.60 0.13 1.30 0.07 - - 7.50 0.17 0.10 0.03 1.13 0.33 0.47 - 0.20 0.03 - - Nacton 0.13 - 0.43 0.03 0.40 - 5.27 0.17 3.37 0.20 1.00 0.50 - - - - 1.67 0.23 0.93 - 0.03 0.03 - - Levington 0.15 0.02 0.02 0.02 0.23 0.12 1.63 0.30 1.50 0.52 0.05 0.05 0.02 - 0.02 0.02 1.07 0.03 0.42 0.02 0.05 0.05 0.02 0.02 Thorpe Bay 0.12 - 0.12 - 0.10 - 1.60 0.16 2.26 0.32 1.04 0.41 - - - - 1.19 0.16 1.09 - 0.24 0.02 - - Crane’s Hill - - 0.05 0.02 - - 0.58 0.27 0.30 0.20 - - - - 0.05 0.05 0.70 0.15 0.23 - 0.13 0.03 0.02 0.02 Shotley Point 0.04 0.01 0.09 - 0.03 - 1.24 0.05 1.36 0.08 - - 0.03 0.01 - - 0.99 0.01 0.37 - 0.01 - - - Stour Erwarton Bay 0.03 0.03 - - 0.03 - 0.70 0.27 1.03 0.30 1.00 0.67 0.07 0.03 0.07 0.07 0.10 0.10 - - 0.07 0.07 - - Holbrook 0.20 0.03 0.07 - 0.03 - 0.93 0.17 1.33 0.27 0.17 - - - - - 0.07 0.07 0.03 0.03 0.07 0.03 - - Jacques Bay 0.09 0.04 0.04 0.01 - - 0.51 0.07 0.24 0.07 0.19 0.08 - - - - - - - - 0.01 - 0.01 0.01 Bradfield Bay 0.03 - - - - - 0.70 0.17 0.30 0.13 - - 0.27 0.20 - - 0.07 0.07 - - 0.13 0.13 0.10 0.07 Stutton - - 0.20 - - - 0.57 0.10 0.33 0.07 0.13 0.13 - - 0.07 0.07 0.17 0.10 0.13 0.10 0.03 0.03 0.10 0.10

33

Table 4: The overall numbers of events/activities and events causing disturbance throughout the study. Activity Number of

events % of total

events n events causing

disturbance

% of disturbance

events

% of activity causing

disturbance

Mean response of

birds to activity (d ± SE)

Mean disruption caused to

birds (i ± SE)

People 86 3.0 26 4.7 30.2 0.57±0.10 1.88±0.13 Joggers 87 3.0 15 2.7 17.2 0.39±0.10 2.27±0.23 Cyclists 52 1.8 12 2.2 23.1 0.46±0.13 2.00±0.21 Walkers 819 28.3 118 21.3 14.4 0.24±0.02 1.68±0.07 Dog walkers 794 27.5 190 34.3 23.9 0.45±0.03 1.89±0.06 Baitdiggers 61 2.1 26 4.7 42.6 0.93±0.15 2.19±0.15 Vehicles 239 8.3 13 2.4 5.4 0.11±0.03 2.00±0.23 Shots 13 0.4 9 1.6 69.2 1.77±0.36 2.56±0.17 Motor vessels 463 16.0 89 16.1 19.2 0.33±0.04 1.71±0.09 Sailing vessels 202 7.0 15 2.7 7.4 0.13±0.04 1.80±0.22 Aircraft 50 1.7 19 3.4 38.0 0.82±0.17 2.16±0.19 Raptors 13 0.4 12 2.2 92.3 1.92±0.26 2.08±0.23 Other 10 0.3 10 1.8 100.0 1.80±0.36 2.00±0.33 ALL 2889 554 0.36±0.01 1.87±0.03

34

Table 5: The numbers of events/activities and events causing disturbance at high and low tides. High tide activity

Number of events

% of total events

% of disturbance events

% of activity causing disturbance

Mean response of birds (d ± SE)

People 32 2.5 5.4 43.8 0.78±0.17 Joggers 34 2.7 4.6 35.3 0.88±0.22 Cyclists 17 1.3 3.5 52.9 1.06±0.28 Walkers 359 28.2 24.3 17.5 0.29±0.04 Dog walkers 348 27.4 39.0 29.0 0.57±0.05 Baitdiggers 0 Vehicles 147 11.6 2.7 4.8 0.09±0.03 Shots 7 0.5 1.9 71.4 1.86±0.51 Motor vessels 213 16.6 12.0 14.6 0.26±0.05 Sailing vessels 90 7.1 1.9 5.6 0.09±0.04 Aircraft 20 1.6 2.7 35.0 0.60±0.21 Raptors 5 0.4 1.9 100.0 2.20±0.37 ALL 1272 0.39±0.02 Low tide activity

People 16 1.5 3.3 31.3 0.44±0.18 Joggers 42 4.0 0.7 2.4 - Cyclists 20 1.9 1.3 10.0 0.15±0.11 Walkers 281 26.5 17.8 9.6 0.17±0.04 Dog walkers 261 24.6 19.7 11.5 0.19±0.04 Baitdiggers 53 5.0 14.5 41.5 0.85±0.15 Vehicles 90 8.5 3.3 5.6 0.13±0.06 Shots 2 0.2 1.3 100.0 2.00±0.00 Motor vessels 176 16.6 25.7 22.2 0.36±0.06 Sailing vessels 90 8.5 3.9 6.7 0.14±0.06 Aircraft 23 2.2 4.6 30.4 0.65±0.23 Raptors 7 0.7 3.9 85.7 1.71±0.42 ALL 1061 0.26±0.02

35

Table 6: An indication of the relative sensitivity of species to disturbance on the estuaries through comparison of the presence of species in background and disturbance counts. Also given is the mean number of each species disturbed per event.

HIGH TIDE LOW TIDE % background

counts with species

(n = 351)

% disturbance counts

with species (n = 241)

Ratio disturbance:

presence

mean no. disturbed per event

n background counts

with species (n = 289)

n disturbance counts

with species (n = 132)

Ratio disturbance:

presence

mean no. disturbed per event

Brent goose 26.8 11.6 0.43 33.5±6.0 28.4 15.9 0.56 133.0±39.2 Black-tailed godwit 33.9 5.8 0.17 34.1±12.6 49.1 12.9 0.26 38.9±9.2 Curlew 41.9 12.0 0.29 5.3±1.2 95.5 19.7 0.21 7.2±2.0 Dunlin 51.9 19.5 0.38 110.6±18.3 79.6 32.6 0.41 191.0±33.6 Golden plover 15.1 2.9 0.19 153.6±85.2 13.8 5.3 0.38 112.3±53.8 Grey plover 39.9 11.6 0.29 27.5±11.4 57.8 12.9 0.22 38.1±20.7 Knot 40.7 12.9 0.32 121.5±29.1 52.9 18.9 0.36 261.7±70.3 Lapwing 25.1 9.5 0.38 50.7±11.9 28.7 9.1 0.32 115.8±27.4 Oystercatcher 48.4 14.9 0.31 55.6±15.1 83.0 22.7 0.27 31.3±6.5 Pintail 8.8 5.0 0.56 5.7±1.5 10.4 2.3 0.22 12.7±4.3 Redshank 81.2 63.9 0.79 27.4±3.5 92.0 54.5 0.59 27.2±7.3 Ringed plover 22.8 8.7 0.38 64.8±16.3 40.1 10.6 0.26 16.0±2.8 Shelduck 72.4 24.1 0.33 13.3±2.5 81.3 17.4 0.21 10.2±2.9 Turnstone 63.8 29.5 0.46 11.2±1.7 68.2 15.2 0.22 9.1±1.9 Wigeon 75.5 37.8 0.50 35.8±4.3 78.2 25.8 0.33 61.8±13.5

36

8. FIGURES

37

Fig. 1: The distribution and approximate extent of the sites studied in the winters 2004/05, 2005/06 and 2006/07 on the Stour and Orwell estuaries. AL is Alnesbourne, BB is Bradfield Bay, BW Bridge Wood, CH Crane’s Hill, EB Erwarton Bay, FR Freston, HB Holbrook Bay, JB Jacques Bay, LE Levington, NA Nacton, PM Pin Mill, PO Pond Ooze, SH Shotley Point, ST Stutton and TB Thorpe Bay.

38

Fig. 2: The mean numbers of birds recorded per 500m of shore during background counts in the study sections of the estuaries in winters 2004/05-2006/07. Site codes as in fig. 1.

39

Fig. 3: The frequencies (number per 500m per hour) of all events on the estuaries over the three winters (top) and the frequencies of events that caused disturbance (bottom).

40

Fig. 4: The effects of season on activities and disturbance.

0

5

10

15

20

25

NOV DEC JAN FEB MAR

Mea

n nu

mbe

r of e

vent

s pe

r cou

nt ±

SE

0

10

20

30

40

50

NOV DEC JAN FEB MAR

Mea

n %

eve

nts

caus

ing

dist

urba

nce

per c

ount

±SE

Fig. 5: The effect of tide on the response of birds.

0

10

20

30

40

50

HIGH FALLING LOW RISING

State of tide

Mea

n %

±SE

of e

vent

s ca

usin

g di

stur

banc

e pe

r cou

nt

41

Fig. 6: The occurrence of events/activities and the disturbance they caused at high and low tide. Dashed lines shows parity. (RA raptors, OT other, SH shots, BA baitdiggers, AIR aircraft, PE people, CY cyclists, JO joggers, SV sailing vessels, VE motor vehicles, MV motoring vessels, WD walkers with dogs and WA walkers only).

High tide

JOSH,RA SV

PEVE

AIR

CY

MV

WA

WD

0

10

20

30

40

50

0 5 10 15 20 25 30

Percent of all events

Perc

ent o

f dis

turb

ance

eve

nts

Low tide

JO

AIR

SHRA

CYPE

BA

SVVE

MV

WAWD

0

10

20

30

40

50

0 5 10 15 20 25 30

Percent of all events

Perc

ent o

f dis

turb

ance

eve

nts

42

Fig. 7: The mean response (disturbance index) of birds to walkers and those with dogs at high and low tide on the estuaries.

0

0.25

0.5

0.75

High Low

State of tide

Mea

n re

spon

se o

f bird

s ±S

E

Walkers Walkers and dogs

Fig. 8: The response of birds to different numbers of dogs.

0.0

0.2

0.4

0.6

0.8

1 2 3+

Number of dogs in party

Mea

n re

spon

se o

f bird

s ±S

E

High Low

43

Fig. 9: The mean response (disturbance index) of birds to different groups of motor vessel at high and low tide on the estuaries.

0

0.5

1

1.5

Ship Yacht Boat Speed

Motor vessel

Mea

n re

pson

se o

f bird

s ±S

E

High tide Low tide

44

Fig. 10: The mean responses of birds to activities at the study sites. Sites codes as in fig. 1.

0

0.2

0.4

0.6

0.8

1

1.2

PO FR BW AL PM NA LE TB CH SH EB HB JB BB ST

Mea

n d

±SE

Upper Orwell Middle & lower Orwell Stour

Fig. 11: The relationship between the number of category events recorded in the study and the frequency with which they caused disturbance. Curve fitted: y=193.6x-0.44. Event codes as per fig. 6.

RA

SH

OT

VE

AIRPE

BA

JOCY

SVMV

WA

WD

0

20

40

60

80

100

0 100 200 300 400 500 600 700 800 900

Number of events recorded

Per

cent

of e

vent

s ca

usin

g di

stur

banc

e

45

Fig. 12: The mean numbers of birds displaced by different activities.

0

100

200

300

400

500

600

700

800

PE JO CY WA WD BA VE SH MV SV AIR RA

Activity

Mea

n nu

mbe

r dis

turb

ed ±

SE

Fig. 13: The relationship between the numbers of events at sites and the disturbance caused to birds on the Orwell (closed circles) and Stour (open) (1-3 denotes winter number at Freston and Levington). Line equation is y=40-0.08x.

FR2BB

EBST

FR1

FR3

ALCH

JB

HB LE2LE1

PO

BW

TB

SH NA PM

0

20

40

60

80

100

0 50 100 150 200 250 300 350 400 450

Number of events per winter

% c

ausi

ng d

istu

rban

ce

46

Fig. 14: The relationships between the number of category events at sites and the rate of disturbance to birds. Only sites with two or more events in each category were used. Site codes as in fig. 1.

Walkers

Walkers with dogs

ALBB

NASHPM

TBBW

LE1LE2

JBHBST

POFR3EB

FR1 CH

FR2

0

20

40

60

80

100

0 50 100 150 200

Number of walkers per winter

% c

ausi

ng d

istu

rban

ce

BW

JB

FR2 & 3AL

STFR1

JB EBLE2

LE1

HB

PM

PO

SHNATB

0

20

40

60

80

100

0 20 40 60 80 100 120

Number of dog walkers per winter

% c

ausi

ng d

istu

rban

ce Sailing vessels

Motoring vessels

TB

ST

NA

PO

SHLE1

BW

FR2

LE2

AL

PM0

20

40

60

80

100

0 10 20 30 40 50 60

Number of sailboats per winter

% c

ausi

ng d

istu

rban

ce

FR1

AL

BW

CH

EBBB

FR2

ST

FR3 LE1

POPM

LE2NA

TB

SH0

20

40

60

80

100

0 20 40 60 80

Number of boats per winter

% c

ausi

ng d

istu

rban

ce

Aircraft

Baitdiggers

EB LE1 BB

HB

BW

PMCH

TB0

20

40

60

80

100

0 5 10 15

Number of aircraft per winter

ST

EB

NAJB

BW

TB

0

20

40

60

80

100

0 5 10 15 20

Number of baitdiggers per winter

47

Fig. 15: The mean number of birds per count at all states of tide in sections of the Stour and Orwell estuaries in 2004/05 to 2006/07 compared with the level of activity recorded (rs = -0.23, n = 180, p = 0.002).

0

500

1000

1500

2000

2500

0 10 20 30 40 50 60 70 80

Number of events

Num

ber o

f bird

s pe

r 500

m s

hore

48

9. Appendices Appendix 1: Maps of the study areas, access routes and site boundaries (dashed lines). Appendix 2: Guidance notes and recording sheets issued to counters. Appendix 3: Literature on bird disturbance and the Stour Orwell estuaries.

49

Appendix 1: Maps of the study areas, access routes and site boundaries (dashed lines). Scale is 1:50000. Crown copyright, all rights reserved: reproduced under licence no. LA100023395 (Suffolk County Council). ORWELL Pond Ooze (red lines), Bridge Wood (blue), Alnesbourne (green) and Freston (brown)

Pin Mill

50

Nacton

Levington

51

Thorpe Bay

Crane’s Hill

52

Shotley

STOUR Erwarton Bay

53

Holbrook Bay

Stutton

54

Bradfield Bay

Jacques Bay

55

Appendix 2: Guidance notes and recording sheets issued to counters. This has been included to help those who wish to replicate this research in their own area.

56

Guidance Notes for recording forms A & B This guidance relates to the survey forms for recording activities taking place at sites on the Stour & Orwell estuaries and the associated disturbance those activities may or may not cause to wildfowl and waders. Please record details as explained below. Please note that in all cases it is better to record more information than less (this may include observations on general bird movements in your survey area). FORM A – Activity form 1 RECORDER DETAILS: Please provide all details requested. 2 SITE DETAILS: Please enter the name of the site. 3 DATE AND TIME: Please enter the date and start and finish times of the count. 4 TIDE: Please record state of tide for survey – low or high 5 CONDITIONS: Please record weather conditions by ringing appropriate words. 6 TIME: Please record the time as and when appropriate (see below) 7 ACTIVITY TIME: Note time of all activities

TYPE OF ACTIVITY: Please record all activities (regardless of disturbance) taking place at the study site choosing from the following categories: Walkers Walkers with dogs Joggers Cyclists Baitdiggers Sailing yacht Motoring yacht Motor boat (speedboat, other launches etc) Ship (container ships, dredgers etc) Helicopter (specify if possible whether military, coastguard or other) Plane Low-flying microlite, hangglider etc Shots Other noises (please specify) Raptors or other birds Other (please specify) Dreads: If birds move without any obvious cause of disturbance please record as a dread. Use a new line for each separate activity. Numbers: Please record the number of people undertaking each activity and the number of dogs present (if any). Record number of dogs on or off leads.

LOCATION: Please indicate the area in which the activity is taking place, choosing from the

following: • Seawall • Footpath (where the path is not on the sea wall) • Write ‘Up’ for upper shore. • Write ‘Mid’ for middle. • Write ‘Low’ for lower shore. • Write ‘Water’ for water-based activities.

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8 MOVEMENT BIRDS: Please record the number and species of birds that move associated with activities

or dreads noted in left-hand column.

RESPONSE: Please record the response of birds using the following 4 point scale: 0 No Disturbance: No disturbance caused to birds. 1 Small Scale Disturbance: Birds to move or fly but return to, or close to, previous

position. 2 Medium Scale Disturbance: Birds take flight returning to different position in study

area. 3 Large Scale Disturbance: Birds take flight and abandon study area. COMMENTS: Use the comments column to record any additional information you feel is

important or useful. FORM B – Count form 1. Site name 2. Date 3. Starting with a count of birds in the study area at the beginning of the 3-hour study period, count the population of birds of each species listed in the study area at hourly intervals to the end of the 3-hour study period (four counts in total). SAFETY: Recorders should ensure that they do not put themselves in a position which could place them, or others, in danger. The Stour & Orwell Estuaries Management Group and The Suffolk Coast and Heaths Unit does not take any responsibility or liability for any actions and subsequent consequences from the activities of recorders.

Thank you for your help ☺

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FORM A Activity Form Stour & Orwell Recreational Disturbance Survey 1. NAME OF SURVEYOR: Contact Tel:

2. SITE:

3. DATE:

TIME: Start: Finish:

4. TIDE:

High Low

5. NOTES:

5. CONDITIONS: (Please ring) Wind speed: None Light Moderate Strong Dominant wind direction: North East South West Rain: None Light Moderate Heavy Cloud cover: None Light Moderate Complete % ice cover:

6. TIME 7. ACTIVITY 8. MOVEMENT

TIME TYPE NO. LOCATION BIRD SPECIES & NUMBERS RESPONSE COMMENTS

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FORM B Stour & Orwell Recreational Disturbance Survey

Hourly Count Recording Form 1. Site:

2. Date:

3. Surveyor:

WILDFOWL WADERS Hourly Count

Count time BG SU WN PT OC RP

GP GV L KN DN BW CU RK TT

Other birds

0 -start

1

2

3 - end

BG – Brent goose SU – Shelduck WN – Wigeon PN – Pintail OC – Oystercatcher RP – Ringed plover GP – Golden plover GV – Grey plover L – Lapwing KN – Knot DN – Dunlin BW – Black-tailed godwit CU – Curlew RK – Redshank TT – Turnstone

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Appendix 3: Literature on bird disturbance and the Stour Orwell estuaries. Anderson, D.W. & Keith, J.D. 1980. The human influence on seabird breeding success: conservation implications. Biological Conservation, 18, 65-80. • Disturbance from recreation seriously disruptive to breeding seabirds in California. Armitage, M.J.S., Austin, G.E., Ravenscroft, N.O.M. & Rehfisch, M.M. 2003. Towards determining the causes of declines in waterbird numbers on the Stour and Orwell estuaries SPA. BTO Research Report No. 338 (report to Posford Haskoning Ltd). • Review document of the likely causes of changes in wintering waterbird populations

on the estuaries. • The greater number of birds recorded on the Orwell at low tide, when they are mostly

foraging, rather than at high tide, when they are roosting, is an indication that disturbance levels on the Orwell may be high as birds usually roost close to foraging areas. Birds feeding on the Orwell Estuary may be choosing to roost at other sites

• Although disturbance cannot be discounted as a cause of the waterbird declines on the Orwell, it is unlikely to have caused the large recent declines that have been recorded unless there has been a large increase in human activity.

Atkinson, P.W., Baker, A.J., Bennett, K.A., Clark, N.A., Clark, J.A., Cole, K.B., Dekinga, A., Dey, A., Gillings, S., Gonzalez, P.M., Kalasz, K., Minton, C.D.T., Newton, J., Niles, L.J., Piersma, T., Robinson, R.A. & Sitters, H.P. 2007. Rates of mass gain and energy deposition in red knot on their final spring staging site is both time- and condition-dependent. Journal of Applied Ecology, 44, 88-895. • Studied factors affecting mass gain of birds staging in Delaware Bay, USA. • Birds arriving late owing to weather or food supply are able to speed up weight gain if

feeding conditions are good to ensure departure on schedule for the breeding grounds.

• Birds need stores for migration but also for up to 2 weeks on arrival in breeding grounds and so are important for survival.

• But there may be costs associated with feeding at a high rate such as reduced vigilance leading to increased predation risk. Increasing late arrival of birds and a reduction in food available at the staging ground has led to an increase in poorly conditioned birds before migration.

• A reduction in the prey available caused by commercial harvest or the time available for feeding through disturbance or predators will impact on the condition of migrating birds.

Babbs, S. & Ravenscroft, N.O.M. 1998. Baitdigging on the Stour and Orwell estuaries. Contract report NB/T/404/97-98, English Nature. • Studied the frequency and impacts of baitdiggers over the winter of 1997/98. • Observations on digging frequency and the responses of birds indicated that the

activity was unlikely to be a major cause of disturbance to birds. • Generally, there were more diggers on the Orwell than the Stour (especially along the

north shore), but the greatest concentration occurred at Wrabness on the Stour. Beale, C.M. & Monaghan, P. 2004. Behavioural responses to human disturbance: a matter of choice? Animal Behaviour, 68, 1065-1069. • Turnstone were provided with supplementary food and their response (the distances

at which birds took flight) to experimental disturbance was recorded. • Birds supplied with additional food took flight at greater distances than birds without. • Suggests that birds with supplementary diets were able to respond earlier, either

because they were in better condition or were more willing to move to an alternative location.

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Beale, C.M. & Monaghan, P. 2004. Human disturbance: people as predation-free predators? Journal of Applied Ecology, 41, 335-343. • Studied the effects of visitors to St Abbs Head NNR on nesting behaviour and

success of cliff-nesting birds. • The presence of people was related to poor nesting success. Increasing visitor

numbers decreased nesting success. At constant visitor levels, nesting success was greater when people were further away.

• Provides good evidence that even when people impart no threat they are perceived as predators by nesting birds.

Belanger, L. & Bedárd, J. 1989. Responses of staging Greater Snow Geese to human disturbance. Journal of Wildlife Management, 53, 713-719. • Studied the effects of disturbance on geese in Canada in spring and autumn. 652

disturbances were recorded in 471 hours of observation (1.4 per hour) and rates were higher in the autumn than spring.

• Low-flying aircraft were prime sources of disturbance. In 40% of disturbances geese ceased feeding afterwards.

• When disturbance exceeded 2 per hour it produced a drop in the number of geese in the reserve the next day.

Belanger, L. & Bedárd, J. 1990. Energetic cost of man-induced disturbance to staging Snow Geese. Journal of Wildlife Management, 54, 36-41. • Studied the energetic consequences of disturbance on geese in Canada by

comparing two responses: birds fly away but resume feeding promptly and birds interrupt feeding altogether.

• Daylight foraging time decreased by 4-51% depending on disturbance. Energy expenditure increased by 3-5% in both responses but energy intake decreased by 1.6% in the former and 3-19% in the latter.

• Birds could compensate by night-feeding and a 4% increase in this activity was required to compensate for energy losses caused by small disturbance, but a 35% increase was required to compensate for interrupted feeding caused by disturbance.

• There were significant energetic consequences of disturbance for the birds but not any noticeable impact on condition of birds.

Bolduc, F. & Guillemette, M. 2003. Human disturbance and nesting success of Common Eiders: interaction between visitors and gulls. Biological Conservation, 110, 77-83. • Used experimental disturbance treatments to study its impacts on breeding eiders,

especially early in incubation. • The frequency of disturbance had a significant negative effect on nesting success

probability. Burger, J. 1981. The effect of human activity on birds at a coastal bay. Biological Conservation, 21, 231-241. • Examined the direct and indirect effects of activity on birds on an urban coastline in

New York, close to an airport, every day for a year. • Apart from aircraft, walkers were the most common activity, followed by bait-diggers.

Sites requiring an access walk of 10-15 minutes were generally devoid of people. • Significantly fewer birds were present when people were present compared with

periods when people were absent. Walkers and especially joggers always disturbed birds, but baitdiggers did not. Rapid movement was regarded as causing more disturbance as it provided a more threatening stimulus.

• Location of birds affected response. Birds on water were not flushed regardless of stimulus as proximity to water appeared to confer a safety advantage.

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• There were pronounced differences in the responses of species. Gulls and terns were least disturbed and more often returned after disturbance, ducks responded by relocating on water and waders flew to other parts of the study area or left altogether. These differences may have been caused by habituation as gulls and terns were present all year and waders were migrants.

• Results suggest that disturbance to gulls is generally transitory as they usually return when the disturbance has passed; ducks and geese are intermediate in response in that they may land nearby but may not return immediately; but waders are vulnerable as they frequently vacate the area when disturbed.

• Recommended restricting disturbance at periods when waders are most vulnerable, especially at roost.

Burton, N.H.K., Armitage, M.J.S., Musgrove, A.J. & Rehfisch, M.M. 2002. Impacts of man-made landscape features on numbers of estuarine waterbirds at low tide. Environmental Management, 30, 857-864. • Related bird numbers on a range of English estuaries (including the Stour and Orwell)

to the presence of sources of disturbance (footpaths, roads, railways and towns). • Numbers of several species were lower close to these features and the study

provided evidence that sustained disturbance can reduce habitat quality of estuaries and that the effects of disturbance may not act just in the short term.

Burton, N.H.K., Rehfisch, M.M. & Clark, N.A. 2002. Impacts of disturbance from construction work on the densities and feeding behaviour of waterbirds using the intertidal mudflats of Cardiff Bay, UK. Environmental Management, 30, 865-871. • Studied the impact of sustained disturbance from development on the feeding

behaviours and densities of wintering birds. • Construction work disturbance reduced the densities and feeding activities of birds on

adjacent mudflats and the overall carrying capacity of the bay, perhaps because of the irregular noise and activities that prevented habituation of birds.

• Results suggested that disturbance may have more than a short-lived effect on local bird populations and may seriously depress local habitat quality.

• Impacts on populations would be likely to occur if reductions in habitat quality associated with disturbance were sufficiently widespread.

Burton, N.H.K., Rehfisch, M.M., Clark, N.A. & Dodd, S.G. 2006. Impacts of sudden winter habitat loss on the body condition and survival of redshank Tringa totanus. Journal of Applied Ecology, 43, 464-473. • Measured the condition and survival rates of birds displaced by flooding of Cardiff

Bay. • Displaced birds had trouble maintaining body weight in the first winter after

displacement compared with birds resident on the mudflats that received displaced birds.

• The survival rates of displaced birds declined owing to a decline in winter survival in the 3 years post-displacement equivalent to a 44% increase in mortality rate.

• Study provides the first empirical evidence that habitat loss impacts on individual fitness in a bird population, which in turn is likely to reduce the local population size.

Erwin, R.M. 1980. Breeding habitat use by colonially nesting waterbirds in two mid-Atlantic US regions under different regime of human disturbance. Biological Conservation, 18, 39-51. • Birds that nest primarily on beaches were restricted to nesting on islands off the

American coast or other poor areas where there was unrestricted access, whereas they nested on beaches where these were protected.

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Fitzpatrick, S. & Bouchez, B. 1998. Effects of recreational disturbance on the foraging behaviour of waders on a rocky beach. Bird Study, 45, 157-171. • Studied the impacts on oystercatcher, curlew and redshank of walkers and other

beach users in summer in Northern Ireland. • Made a total of 185 hours observation and also recorded the numbers of birds

present at sites at 0.5hour intervals. Recorded 319 disturbances to birds (1.7 per hour, although the authors suggest that 3-4 per hour is more normal).

• Scan rates of feeding birds increased with fast human movements, but disturbance did not affect probing rates on mudflats. Capture rates of prey actually increase in the vicinity of human disturbance suggesting that when undisturbed birds might not be feeding at maximum efficiency.

• Rapid movements of humans had more impacts on birds but there were no impacts from dogs. Most birds that remained on the beach after disturbance resumed feeding within 1-2 minutes.

• Effects of disturbance were small overall, affecting the time available for feeding through later arrival and earlier departure times and by affecting feeding behaviour, but birds also spent a large amount of time resting during the feeding period suggesting that birds could compensate for lost time.

• The only additional feeding available to birds on this beach was through delaying departure to roost by feeding on the upper shore, although this was more subject to disturbance, suggesting that at this beach birds were unable to compensate for lost feeding time by feeding more. Instead they appeared to cope with disturbance through habituation to benign human presence.

Gill, J.A., Sutherland,W.J. & Watkinson, A.R. 1996. A method to quantify the effects of human disturbance on animal populations. Journal of Applied Ecology, 33, 786-792. • Studied the impact of disturbance (roads) on the distributions of geese feeding in

fields in Norfolk with the assumption that disturbance causes lower consumption of resources in disturbed patches.

• Witnessed 27 disturbances in 62 hours of observation (0.43 per hr or one every 2.5 hrs). Those fields on which geese were disturbed most often were used less than fields on which geese were disturbed rarely.

• The distance from the flock to the nearest road was related negatively to the disturbance rate as well as to the proportion of the crop in fields that was not consumed.

• Animals respond to disturbance from humans in the same way as they respond to the risk from predation, by avoiding areas of high risk, either completely or by using them for short periods, and pink-footed geese deplete the resource in fields in Norfolk according to the risk of disturbance associated with those fields.

. Gill, J.A., Norris, K. & Sutherland, W.J. 2001a. Why behavioural responses may not reflect the population consequences of human disturbance. Biological Conservation, 97, 265-268. • Human disturbance is only important if it affects the survival or fecundity of wildlife

and hence causes a population to decline. • Suggests that an observed sensitivity to disturbance may be interpreted as a

response to a high availability of alternative habitat. Birds that are forced to remain owing to lack of alternatives may be those most adversely affected by disturbance.

• The costs of moving in response to disturbance may not be high for birds that feed in flocks on readily available resources, or for those for which not moving may expose them to predation e.g. wildfowling. It may be high for birds that feed on mobile or aggregated prey, or birds that are territorial or experience interference from others in feeding

64

Gill, J.A., Norris, K. & Sutherland, W.J. 2001b. The effects of disturbance on habitat use by black-tailed godwits Limosa limosa. Journal of Applied Ecology, 38, 846-856. • Studied the impacts of disturbance on resource use by birds in East Anglian

estuaries. • The Deben, Orwell and Colne estuaries had higher levels of activity than the Alde and

Blackwater and the majority of human activity on each of the estuaries was shore-based.

• There was no relationship between human activity and the presence of birds and the rates of depletion of resources were not greater in sites with less human activity.

• There was no evidence that the presence of humans, marinas or footpaths reduced the number of godwits that was supported at a range of spatial scales.

Goss-Custard, J.C. & Durrell, S.E.A. le V. dit 1990. Bird behaviour and environmental planning: approaches in the study of wader populations. Ibis, 132, 273-289. • Review article. • If the density of birds rises in an area, then rates of depletion of food and interference

during feeding will increase and food intake will decrease. • Increased aggression, territoriality and density impacts on feeding rates of waders

and therefore increases mortality. • The overall population size can be affected greatly by the winter mortality of young

birds. Goss-Custard, J.D., Triplet, P. Sueur, F. & West, A.D. 2006. Critical thresholds of disturbance by people and raptors in foraging birds. Biological Conservation, 127, 88-97. • Modelled the effects of disturbance on oystercatchers. The model assumed that the

same birds in an area are disturbed repeatedly, but in reality only a proportion of birds present may be so.

• Disturbance equated to 0.5-1.7 events per daylight/hour by people and raptors. The highest disturbance frequency would only have increased bird mortality slightly in a mild winter while prey remained abundant, but mortality started to increase at the lowest disturbance rates when prey was scarce. When severe weather was added, the critical threshold of disturbance was only 0.2-0.3 per hour.

• People and raptors caused similar effects on birds. A frequency of flying caused by disturbance in autumn and early winter of up to 1.5 per hour is not damaging, but as food becomes depleted by midwinter, this disturbance threshold fell to 0.5 per hour.

• Results indicate that not all avoidance behaviours associated with disturbance may actually affect the fitness of birds, especially early in the winter.

Hill, D., Hockin, D., Price, D., Tucker, G., Morris, R. & Treweek, J. 1997. Bird disturbance:improving the quality and utility of disturbance research. Journal of Applied Ecology, 34, 275-288. • Review article. • In general, birds appear to habituate to continual noises as long as there are no

occasional loud noises. Vehicles and vehicle movements are tolerated more than people.

• Displacement of wintering birds must lead to one or more of: i) higher densities on other sites that are currently by other birds; ii) a greater proportion of birds being forced to use suboptimal feeding habitat; and iii) direct mortality if no alternative areas can be found.

• Disturbance of habitat loss will give rise to a reduction in food accessibility leading to movements of birds to other sites and hence increased density. This in turn leads to food depletion or interference between birds such that intake is affected, thus affecting mortality rate.

65

Keller, V.E. 1988. Human disturbance of eider crèches on the Ythan estuary. Nature Conservancy Council. • Study focussed on the high tide period. • Disturbance of roosting crèches was frequent (0.69 per hour) but rare when crèches

were on the water (0.11 per hour). Most caused by fishermen, with walkers next. Disturbance by water-based activity rare because the narrow estuary restricted these activities.

• Repeated disturbance caused crèches to remain more frequently on the water and this may increase energy expenditure as well as predation risk.

Klein, M.L., Humphrey, S.R. & Percival, H.F. 1995. Effects of ecotourism on the distribution of waterbirds in a wildlife refuge. Conservation Biology, 9, 1454-1465. • Studied the impacts on birds of cars and their passengers along drives and

crossdikes in a reserve in Florida, USA. • Resident birds were less susceptible to disturbance than migrants, and migrants were

most susceptible when they first arrived, particularly from mid October to mid December.

• All migrant ducks (especially teal and pintail) avoided humans before mid December, but some species became less sensitive through the winter.

• There were distinct differences in the response of species to disturbance, and some species such as dunlin stayed further away from areas with greater numbers of cars.

• The study recommended that visits by tourists should be controlled in early winter. Madsen, J. 1985. Impact of disturbance on field utilisation of pink-footed geese in West Jutland, Denmark. Biological Conservation, 33, 53-63. • Studied the impacts of roads and landscape features on geese in autumn and spring

and measured the distance at which birds took flight in response to cars. • Larger flocks took flight at greater distances, but response distance decreased

through the winter. Flocks of 400-600 took flight at 500m in autumn and 3-400m in spring. Probably related to shooting season being September to December.

• The more cars, the more disturbance caused to geese in fields, and birds took flight at greater distance.

• An obstruction to the open view on one side of a field had no effect on goose utilisation of the field, but obstruction to more than one side of field did affect utilisation – and smaller fields were used proportionately less.

• Concluded that disturbance that puts birds to flight and obstructions that hide potential predators affect goose utilisation of the landscape.

Madsen, J. 1995. Impacts of disturbance on migratory waterfowl. Ibis, 137 (Supplement), S67-S74. • Review article of disturbance, especially to geese in Denmark. • Increased disturbance on staging areas during migration can lower probability of

successful breeding the following summer. • Birds can compensate for disturbance by altering behaviour or habituating. • Impacts of disturbance may only manifest themselves after winter. • Impacts of disturbance are expected to be especially high in late winter when food

reserves are depleted and energy demands are high. • Disturbance can be regarded as equivalent to habitat loss, although its effects are

reversible. • There may be a threshold of activity below which site use is unaffected by humans. Madsen, J. 1998. Experimental refuges for migratory waterfowl in Danish wetlands. I. Baseline assessment of the disturbance effects of recreational activities. Journal of Applied Ecology, 35, 386-397.

66

• Examined the impacts of disturbance on passage waterfowl in a coastal wetland. • Fishing, windsurfing and sailing were not important sources of disturbance (primarily

owing to seasonal effects, although birds reacted to the presence of windsurfers at large distances).

• Bird numbers were more depleted in areas where there was greater human activity. • Birds that have limited feeding opportunities (e.g. wigeon) are more vulnerable to

disturbance. Madsen, J. 1998. Experimental refuges for migratory waterfowl in Danish wetlands. II. Tests of hunting disturbance effects. Journal of Applied Ecology, 35, 398-417. • Examined the responses of birds to the creation of disturbance-free areas (hunting

exclusions) in a coastal wetland. • Birds that were hunted before the creation re-distributed according to the positions of

hunting-free areas (a 6-8 fold increase in geese and 4-50 fold increase in ducks), indicating that before creation hunting caused a displacement of birds owing to disturbance.

Mitchell, J.R., Moser, M.E. & Kirby, J.S. 1988. Declines in midwinter counts of waders roosting on the Dee estuary. Bird Study, 35, 191-198. • Frequent disturbance may cause waders to abandon traditional roosts. • Frequent disturbance caused large declines in populations of waders, although birds

continued to use traditional feeding areas, and resulted in energetic costs owing to larger flight distances.

Mooij, J. 1991. Numbers and distribution of grey geese (genus Anser) in the Federal Republic of Germany, with special reference to the lower Rhine region. Ardea 79, 143-158. • Shooting bans in Germany have led to major concentrations of geese in southern

Germany. Musgrove, A.J., Clark, N.A., Gill, J. & Ravenscroft, N.O.M. 2000. A review of wildfowling on the Stour estuary. BTO Research Report No. 247 (Report to English Nature). • Wildfowling occurs at a low level compared with other activities. • Wildfowling clubs reported an apparent increase in walkers on the estuary in recent

years, especially close to areas where new car parks had been constructed. • WeBS count data indicated that disturbance was caused by walkers on 32% of

occasions. Dogs accompanied walkers on 50% of occasions, caused disturbance on 36% of occasions and were not considered to be more disturbing than people alone.

• Powered boats were considered to be more disturbing than un-powered boats. Musgrove, A.J., Langston, R.H.W., Baker, H. and Ward, R.M. (eds.) 2003. Estuarine Waterbirds at Low Tide: the WeBS Low Tide Counts 1992/93 to 1998/99. Wader Study Group/British Trust for Ornithology/Wetlands and Wildfowl Trust/Royal Society for the Protection of Birds/Joint Nature Conservation Committee, Thetford, 310pp. • Summaries of the first seven years of low tide counts of birds wintering in British

estuaries (under WeBS) and maps of bird distributions. Although the data is not systematic, counters recorded activities affecting birds during counts.

• Walkers and those with dogs and bait-diggers were the most frequent activities but vehicles, shooting and boats caused disturbance more usually. Rates of disturbance were similar to those caused by raptors.

Rehfisch, M.M., Insley, H. & Swann, R. 2003. Fidelity of overwintering shorebirds to roosts on the Moray Basin, Scotland: implications for predicting impacts of habitat loss. Ardea, 91, 53-70.

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• Loss of roosts increases the probability of birds being forced to make extra or longer flights that are energetically demanding and could decrease their probability of survival.

• Most species were highly faithful to particular roost sites. • Selection of roost sites depends on (in descending priority): shelter, proximity to

feeding areas, lack of disturbance and risk of predation. • Loss of roosts may lead to a decline in usage of feeding grounds, but a change in

roosting conditions is likely to be less detrimental to birds than a loss of feeding area. Owens, N.W. 1977. Responses of wintering brent geese to human disturbance. Wildfowl, 28, 5-14. • Studied the amount of feeding time lost and extra time spent in flight of brent geese

on the Essex coast and estuaries (Maplin sands). • There was usually small scale disturbance owing to noises or aircraft, but birds often

left the study area after disturbance by people. Any plane below 500m and up to 1.5km away would disturb birds and helicopters caused panic. Ideally aircraft should not fly below 500m over estuaries.

• There was a decrease in the distance at which birds were put up through winter. Before New Year, about 33% of people at 100m put birds up, whereas after New Year, only 12% did. There was also a tendency for larger flocks to take flight at greater distances

• Birds became habituated to most sounds, but not to unexpected ones such as gunshots. When disturbances occurred very frequently birds appeared to become more easily disturbed on subsequent occasions.

• Baitdiggers and birdwatchers at low tide and people on the shore at high tide were the main causes of disturbance. In 168 hrs of observation, human disturbance that caused birds to fly occurred on average once every 81mins. 48% of disturbance was by people (mostly on the shore), 39% by aircraft, 9% by loud noises and 4% by small boats. Overall disturbance rate was 0.68 events per hour.

• Disturbance on the shore at high tide caused a greater loss of feeding time owing to restricted availability of feeding areas and crowding of birds in these areas. Therefore, walkers on the shore at high tide caused a greater loss of feeding time than baitdiggers.

Stillman, R.A. & Goss-Custard, J.D. 2002. Seasonal changes in the response of oystercatchers Haematopus ostralegus to human disturbance. Journal of Avian Biology, 33, 358-365. • Studied the foraging behaviour of birds and their responses to disturbance in the Exe

estuary. • As winter progresses, feeding conditions deteriorate and bird energy requirements

increase, so birds spend longer periods feeding and less compensating for disturbance. Later in winter, birds approach a disturbance source more closely and return more quickly i.e. their response is less when they are having more difficulty surviving.

• Their results have implications for studies that assume that disturbance impacts on birds owing to their behavioural responses. The opposite may be the case as oystercatchers responded more to disturbance at times when they were more able to compensate for lost feeding time (although the authors acknowledge that their results may have been caused by habituation of birds to the experimental cause of disturbance that was also relatively minor).

• Compensation for lost feeding time caused by disturbance on the Exe occurs by feeding for longer.

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• Suggest that conservation effort should be directed at species that show large behavioural responses to disturbance even though they are already having difficulty meeting their requirements.

Swennen, C., Leopold, M.F. & Bruijn, L.L.M. de 1989. Time-stressed oystercatchers, Haematopus ostralegus, can increase their intake rate. Animal Behaviour, 38, 8-22. • Oystercatchers are able to compensate for lost time by increasing their feeding rate in

the remaining time. Taylor, K., Anderson, P., Taylor, R.P., Longden, K. & Fisher, P. 2005. Dogs, access and nature conservation. English Nature Research Report No. 649. English Nature, Peterborough. • A review of dogs and nature conservation issues. • Some studies have shown that birds flush earlier (i.e. at a greater distance) when

approached by a person with a dog than by a person without a dog. This has been shown through observation of incubating waders, wintering waders and through experimental manipulation of nesting plovers. One study of feeding passerines showed no difference in the distance at which birds flushed when approached by a person with or without a dog.

• The principal issue of concern for conservationists is whether dogs can influence the population size that a site may be able to support. The only evidence that dogs may have the potential to directly impact breeding success is anecdotal evidence of dogs taking chicks. There is no evidence of dogs taking eggs, but the use of cameras at the nests of ground-nesting birds has shown that dogs will visit nests and flush adult birds. The flushed birds may betray the whereabouts of the nest and leave it vulnerable to predation, hence the high predation rates (by crows) recorded for some ground-nesting species may be attributable to disturbance from dogs.

Tuite, C.H., Hanson, P.R. & Owen, M. 1984. Some ecological factors affecting winter wildfowl distribution on inland waters in England and Wales, and the influence of water-based recreation. Journal of Applied Ecology, 21, 41-62. • An study of recreation on inland confined freshwater bodies in the UK. • The greatest impact on winter wildfowl numbers was associated with the presence of

fishing, sailing and rowing. Verhulst, S., Oosterbeek, K. Ens, B.J. 2001. Experimental evidence for effects of human disturbance on foraging and parental care in oystercatchers. Biological Conservation, 101, 375-380. • Studied the impacts of disturbance on the breeding success of birds in the

Waddensea, Holland. • Disturbance caused reduced intake rates of food by foraging birds as they spent less

time on mudflats. • Ultimately, increased disturbance resulted in a reduction in the quality of parental

care. West, A.D., Goss-Custard, J.D., Stillman, R.A., Caldow, R.W.G., Durrell, S.E.A. le V. dit & McGrorty, S. 2002. Predicting the impacts of disturbance on shorebird mortality using a behaviour-based model. Biological Conservation, 106, 319-328. • Used data gathered during studies of predation by oystercatchers on bivalves and

earthworms in the Exe estuary. • The model predicted that continuous disturbance had little effect on bird survival at

low population levels. At greater population sizes numerous minor disturbances reduced survival more than fewer major disturbances when only 10% of the estuary was affected by disturbance, as the former were spread over a greater number of

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feeding areas even though both disturbed the same total area. (i.e. a group of bait-diggers could cause less disturbance overall than the same number of individuals spread throughout an estuary).

• The differences between types of disturbance were lost when greater areas of the estuary were disturbed (50%) and bird survival was reduced owing to the reduction in available feeding area.

Yalden, P.E. & Yalden, D.W. 1990. Recreational disturbance of breeding Golden Plovers Pluvialis apricarius. Biological Conservation, 51, 243-262. • Studied the impact of walkers in the Peak District. • One dog to 25 walkers was a typical ratio and 60% of dogs were not kept on leads. • Birds were more sensitive to dogs than to people. • Low breeding success was caused by avoidance behaviour by birds at the start of the

breeding season. Wader Study Group Bulletin, 68 (Special Issue), 1993: Disturbance to waterfowl on estuaries. Cayford, J. 1993. Wader disturbance: a theoretical review. Wader Study Group Bulletin, 68, 3-5. • Brief disturbance can result in birds being deprived temporarily of feeding habitat.

Sustained disturbance can result in a long-term loss of feeding habitat and a reduction in feeding opportunity. In theory, the only difference between disturbance and development is that the effects of the former are localised, temporary and reversible. Effects on birds may therefore be similar to development and habitat loss.

• Birds can adjust to disturbance by increasing feeding intake or by feeding at different times.

• Effects of disturbance are likely to be additive. Smit, C. & Visser, G.J.M. 1993. Effects of disturbance on shorebirds: a summary of existing knowledge from the Dutch Wadden Sea and Delta area. Wader Study Group Bulletin, 68, 6-19. • Disturbance can be defined as 1. any situation in which a bird behaves differently

from its preferred behaviour, or 2. any situation in which human activities cause a bird to behave differently from the behaviour it would exhibit without the presence of that activity.

• Small aircraft and walkers are principal forms of disturbance – forms with predictable behaviour less so. The former also cause birds to take flight at large distances – walkers within 250m usually caused disturbance to oystercatchers. Cars, farming and dogs caused less disturbance. Kayaks and sailing boats disturbed birds more often than motor boats.

• There were differences between species: redshank and curlew tend to take flight at more than twice the distance of gulls, plovers and oystercatchers. Large flocks more easily disturbed.

• Birds may habituate to disturbance: flight distance was lower on the Waddensea than in the Banc d’Arguin where oystercatchers may be put up at 4-500m. Likewise curlew in Holland could be approached to 100m in cultivated grassland whereas on more isolated saltmarsh flight distance was 200m. Dunlin may be approached to 10-20m in areas where visitor activities are high but may take flight at large distances in less disturbed areas.

• Flight distance is also influenced by behaviour of people. One person generally disturbs less than a group and baitdiggers working at the same spot for some time are tolerated at shorter distances than a walking person.

• Helicopters and small aircraft caused more disturbance than jets and some species were more tolerant than others of aircraft disturbance. Brent geese reacted most

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strongly, together with redshank and curlew. Aircraft at heights>300m rarely disturbed birds, whereas those <150m usually did. Small and slow flying aircraft are considered to be the among the most disturbing events in the Wadden Sea. Birds may habituate to aircraft and helicopters where their movements are predictable but otherwise these cause panic.

• Speed at which birds return to feeding area differs between species. Intake rates of birds make increase after disturbance.

Koolhaas, A., Dekinga, A. & Piersma, T. 1993. Disturbance of foraging knots by aircraft in the Dutch Wadden Sea in August-October 1992. Wader Study Group Bulletin, 68, 20-22. • Studied the responses of knot on a sandflat complex close to a practice bombing

range for jets. • When aircraft were present the numbers of knot was much lower than on days

without aircraft, and during these days birds were much less approachable and more restless. There were also indications that birds were more sensitive earlier in the winter, especially after they had just arrived, and also perhaps more sensitivity to aircraft during fogy conditions, and low-flying light aircraft caused birds to leave the study area.

• Although there was some reason to believe that birds became adjusted to disturbance, this holds only for those birds that were present in the study area throughout the season. Overall, the presence of aircraft is likely to decrease severely the carrying capacity of the area for birds.

Stock, M. 1993. Studies on the effects of disturbances on staging brent geese: a progress report. Wader Study Group Bulletin, 68, 29-34. • Studied the effects of disturbance at saltmarsh in a part of the Wadden Sea used

heavily by tourists. Up to 200 people occurred simultaneously on some study days in spring.

• 143 hours of observation: resulting in a disturbance rate of 0.22-6.9 disturbances per hour (mean disturbance level 2.19 per hour).

• Non-human stimuli always disturbed geese. Of human stimuli, people caused disturbance on 93% of occasions, cars 89%, helicopters 70%, light aircraft 69%.

• Larger numbers of birds disturbed by helicopters and small aeroplanes and birds took longest to resume feeding after this disturbance.

• Rate of disturbance regarded as high at 2.19 per hour. Townshend, D.J. & O’Connor, D.A. 1993. Some effects of disturbance to waterfowl from bait-digging and wildfowling at Lindisfarne National nature Reserve, north-east England. Wader Study Group Bulletin, 68, 47-52. • Charted the numbers of waders and wildfowling in a part of the NNR during periods of

bans and restriction of baitdigging. No data on visitation rates, but presumably high as large numbers of diggers were recorded and the adult lugworm population was completely denuded, with an estimated 4 million worms taken in three winters.

• During periods of baitdigger bans, the proportions of wintering shelduck, redshank, wigeon and godwits in the NNR using the dug areas increased many-fold (119-744%), suggesting that the presence of baitdiggers prevented full use of the area by birds.

Kirby, J.S., Clee, C. & Seager, V. 1993. Impact and extent of recreational disturbance to wader roosts on the Dee estuary: some preliminary analysis. Wader Study Group Bulletin, 68, 53-58. • Voluntary wardens patrolling west Kirby beach recorded the potential sources and

causes of disturbance to waders during winter high tides in 1986/87 to 1990/91. They made 339 visits and 1007 hours of observations, with the average duration of a visit

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being about 3 hours. Also, they ranked the level of disturbance 1-4, with 4 being the most severe involving a permanent move of birds out of the estuary.

• The majority of potential sources of disturbance were walkers (50% of total) and dogs (26-41%). Level of usage was sometimes as high as 200 per hour, more usually less than 50 per hour. Potential for disturbance increased over the five year period, but actual disturbance rates did not.

• The majorities of actual disturbance events were caused by dogs (27-72% per year) and walkers (20-34% per year). Overall disturbance rates were between 0-3 per hour, with less than one on the vast majority of occasions.

• In most cases, particularly the most frequent causes of disturbance (walkers and dogs), birds were not disturbed heavily (just re-located nearby or returned soon after).

Goss-Custard, J.D. & Verboven, N. 1993. Disturbance and feeding shorebirds on the Exe estuary. Wader Study Group Bulletin, 68, 59-66. • People are most attracted to sandflats and baitdigging and dog-walking were

common there, but most feeding occurred on softer sediments where birds were disturbed little.

• Over the winter, at least 66% of feeding occurred when people seldom occurred in the feeding area, but food quality in areas where birds fed undisturbed and intake rates at less optimum periods such as at night, were poor, meaning that effectively disturbance may occur for over 50% of the time birds were feeding during the winter. In parts where disturbance occurred, birds could lose 33-50% of intake.

• But birds can adjust for this by increasing intake rates, re-scheduling foraging activities, feeding elsewhere or habituating although his depends on the extent to which people move about and the number of people (single baitdiggers or anglers would cause little disturbance).

• Young birds may be more vulnerable to the effects of disturbance being the least efficient foragers and poorest competitors, exacerbated in cold weather. Overall population size can be affected greatly by winter mortality of young birds.

Fox, A.D., Bell, D.V. & Mudge, G.P. 1993. A preliminary study of the effects of disturbance on feeding wigeon grazing on eel-grass Zostera. Wader Study Group Bulletin, 68, 67-71. • Studied the impacts of disturbance on wigeon feeding at four sites: 2 in Scotland and

two in Devon. • Showed that birds with an already restricted feeding time e.g. wigeon that feed on

Zostera beds exposed by the tidal cycle and are limited to four two-hour periods every 24 hours, are more prone than many other species to the effects of disturbance.

• Birds tolerated disturbance in the early stages of the feeding period, but when it occurred after Zostera had been exposed and birds were standing on the mudflat, birds abandoned the feeding area.

• Disturbed bird lose 25-50% of feeding time available. Owen, M. 1993. The UK shooting disturbance project. Wader Study Group Bulletin, 68, 35-46. • Although dogs and baitdiggers were the most frequent sources of disturbance, the

amount of disturbance in terms of time lost feeding was small compared with shooting and light aircraft.

Davidson, N.C.& Rothwell, P.I. 1993. Human disturbance to waterfowl on estuaries: conservation and coastal management implications of current knowledge. Wader Study Group Bulletin, 68, 97-105. • Summarises the proceedings of Wader Study Group Bulletin, 68. Points out that:

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• In some cases disturbance has been shown to cause decreases in the numbers of birds using an estuary, but more usually this involves cessation of feeding or local movements

• As some waterfowl that are subject to disturbance are migratory, any effect of disturbance (such as poor condition caused by interrupted feeding) might only manifest itself thousands of miles away on the breeding grounds. On the breeding grounds, arctic waders may need to draw on reserves soon after arrival if snow-melt is late and weather conditions are bad

• Impacts of disturbance could be especially severe during cold weather when fat reserves of wintering birds are exhausted.

• Effects of disturbance vary enormously from estuary to estuary and birds may habituate on some estuaries by not others. Some bird species are more prone than others: e.g. brent geese, redshank and curlew appear more nervous than oystercatcher, turnstone and dunlin.

• Several studies have found that the most widespread and long-lasting disturbance comes from slow-moving aircraft. On the shore, moving people and dogs generally cause more disturbance than static people.

• The size of the available area affects impacts of disturbance: on small estuaries there may be few alternatives and persistent disturbance may make its use untenable.

Ibis, 149 (Supplement 1), 2007: Birds and recreational disturbance (British Ornithologists’ Union Meeting 2005). Drewitt, A.L. 2007. Birds and recreational disturbance. Ibis, 149 (Suppl. 1), 1-2. • Most work on disturbance and birds has focused on behaviour rather than the

consequences of disturbance for populations and as such do not necessarily provide evidence of an impact.

• Research must establish whether disturbance reduces the numbers of birds on the affected site.

Bathe, G. 2007. Political and social drivers fro access to the countryside: the need for research on birds and recreational disturbance. Ibis, 149 (Suppl. 1), 3-8. • Review article concerned primarily with the CRoW Act. • 55% of the open access land covered under the act is designated as SSSI where

wildlife is conserved legally. • Much work available on disturbance caused by access is of limited application.

Research showing effects on birds such as stress, avoidance of certain areas or increased energy expenditure is relevant only where this could reveal a population effect within the designated area (SSSI or SPA).

Gill, J.A. 2007. Approaches to measuring the effects of human disturbance on birds. Ibis, 149 (Suppl. 1), 9-14. • The principal way in which humans can impact on wildlife is by altering the ability of

animals to exploit important resources, through animals avoiding areas where humans are present. But in many studies, the numbers of animals that would use the site in the absence of disturbance is not known.

• Animals may remain in an area that is disturbed because the cost of moving to a new location is too great or because food resources are greater or predation risk is lower than in the alternative site. Animals that move readily in response to disturbance may do so because the alternative locations are plentiful or because the costs of moving are small.

• A behavioural response to disturbance is not sufficient to determine vulnerability to presence of humans as the same response can result from opposing circumstances.

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• Populations in which density dependence is strong (causing increased mortality through higher rates of depletion of available prey [and interference during feeding] or increased vulnerability to predators) can suffer severe declines in population from only small re-distributions in response to disturbance.

Langston, R.H.W., Liley, D., Murison, G., Woodfield, E. & Clarke, R.T. 2007. What effects do walkers and their dogs have on the distribution and productivity of breeding European Nightjar Caprimulgus europaeus. Ibis, 149 (Suppl. 1), 27-36. • Disturbance may impact on birds at the population level by flushing them from nests

that are then predated. • There was a significant relationship between nest failure and disturbance attributes

as nest failure was more likely close to footpaths and with the amount of paths in close proximity.

Stillman, R.A., West, A.D., Caldow, R.W.G. & Durrell, S.E.A. le V. dit 2007. Predicting the effect of disturbance on coastal birds. Ibis, 149 (Suppl. 1), 9-14. • Disturbances of all scales have similar effects on birds, as they exclude birds from

areas that would otherwise be used for feeding or roosting (and as such the effects are the same as those caused by loss of habitat) and increase the energy demands of birds by causing them to take flight, reducing the time they have to feed or decreasing feeding efficiency.