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(2004),

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Blackwell Publishing, Ltd.

The state of play of farmland birds: population trends and conservation status of lowland farmland birds in

the United Kingdom

RICHARD D. GREGORY,

1

* DAVID, G. NOBLE

2

& JOHN CUSTANCE

3

1

The Royal Society for the Protection of Birds, The Lodge, Sandy, Bedfordshire SG19 2DL, UK

2

British Trust for Ornithology, Thetford, Norfolk IP24 2PU, UK

3

Department for Environment, Food and Rural Affairs, 5/D12 Ashdown House, 123 Victoria Street,

London SW1E 6DE, UK

Many bird species of lowland farmland have declined substantially in the United Kingdomover the past 30 years. Declines among farmland specialists are steeper than for generalists andwere most rapid for these specialists in the 1970s and 1980s. These changes have been linkedto increased agricultural intensification and are reflected in Red or Amber conservation concernstatus for many common farmland species, as well as for rarer ones. We review long- andshort-term population trends and the conservation status of lowland farmland birds in theUK using the latest available information from bird surveys, and examine patterns amongspecies. Analyses of demographic parameters suggest broadly that the key factor drivingpopulation changes of seed-eating and migrant birds is overwinter survival, whereas for manynon-passerine species population growth appears to be limited by productivity. Populationtrends for a suite of lowland farmland species were first combined in the UK Government’sheadline wild bird indicator published in 1998. This ‘Skylark index’ as it is sometimes knownwas intended to reflect the health of the wider countryside and struck a chord with the publicand decision-makers. We look at the behaviour of the composite indicator and explore thepopulation dynamics of the increasing and declining species separately. Simple models ofpopulation growth in these groups are then used to explore plausible scenarios for deliveringthe Government’s Public Service Agreement target to reverse the long-term decline in thenumber of farmland birds by 2020.

THE STATUS OF FARMLAND BIRDS

Although a series of studies conducted in the 1980sand early 1990s had focused on problems facingbirds in agricultural habitats (O’Connor & Shrubb1986, Potts 1986, Galbraith 1988, Green & Stowe1993, Evans & Smith 1994, Green & Griffiths 1994,Green

et al

. 1997, 2000), the scale of problems fac-ing lowland farmland birds in the United Kingdomdid not become fully apparent until the mid-1990s(Marchant

et al

. 1990, Gibbons

et al

. 1993, Fuller

et al

. 1995). Fuller

et al

. (1995) reviewed the statusof a range of bird species and was able to show a

preponderance of declines in geographical range andpopulation size among lowland farmland birds. Whatwas striking was not only the scale of the declines,but also the similarity in their pattern and timingacross species. Subsequent analysis has confirmedand extended our understanding of the trend pat-terns (Siriwardena

et al

. 1998, Fewster

et al

. 2000).It is thanks to the existence of long-term bird moni-toring schemes and bird atlases, both largely depend-ent on skilled volunteers, that we have such adetailed picture and understanding of farmland birddeclines (Marchant

et al

. 1990, Gibbons

et al

. 1993,Fuller

et al

. 1995, Siriwardena

et al

. 1998, Aebischer

et al

. 2000a, Fewster

et al

. 2000).A raft of subsequent studies has explored the eco-

logy and conservation of lowland farmland birdsand there is compelling and extensive evidence to

*Corresponding author.Email: richard.gregory@rspb.org.uk

2

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show that the declines among farmland birds in theUK, and elsewhere in north and west Europe, havebeen driven by agricultural intensification (Tucker &Heath 1994, Krebs

et al

. 1999, Aebischer

et al

. 2000a,Chamberlain

et al

. 2000, Donald

et al

. 2001).The plight of farmland birds as a group was high-

lighted further by the revision of the Red Data Listin 1996, which was the first to place strongly declin-ing, but still relatively widespread and commonbirds in the highest category of conservation concern(Gibbons

et al

. 1996). Around one-third of the birdson the resulting Red list were associated with farm-land. Although some were rare or localized speciesthat were already of high conservation concern suchas Cirl Bunting

Emberiza cirlus

and Stone Curlew

Burhinus oedicnemus

, others such as Grey Partridge

Perdix perdix

, Skylark

Alauda arvensis

and CornBunting

Miliaria calandra

were widespread and newadditions to the Red list. All of these species havebeen given high priority within the UK Govern-ment’s Biodiveristy Action Plan, which has acted asa stimulus to research and conservation action, andimportantly has defined targets for species recovery.Subsequent revisions of the population status of theUK’s birds have confirmed the general pattern ofdecline in lowland farmland birds, with further addi-tions to the Red list such as Starling

Sturnus vulgaris

and Yellowhammer

Emberiza citrinella

(Gregory

et al

. 2002). However, the adoption of a wildlifeindicator based on populations of breeding birds(Anon. 1998, 1999, 2002) has more recently pro-vided a very significant impetus and focus for farm-land bird research.

Here we focus on birds that are associated withlowland farmland in the UK, i.e. are to some degreedependent upon and/or have significant populationsin this habitat (Gibbons

et al

. 1993, Gregory & Baillie1998, Gregory 2000) rather than taking a broader viewof all birds that occur on farmland, other farmlandtypes and open habitats (e.g. Newton 2004).

The farmland bird index

The wild bird index, which is sometimes popularlyknown as the ‘Skylark index’, is one of the govern-ment’s 15 headline indicators of

Quality of Life

(Anon. 1998, 1999, 2002). These are the key indi-cators that the government is using to measure theUK’s progress towards sustainable development. Theycover issues of everyday concern to people such aseducation, health, jobs, the environment, crime andhousing. The bird indicator was developed to give a

broad summary of the general health of wildlife inthe British countryside. Although covering most com-mon species, it is particularly focused on two keyhabitats – ‘farmland’, which covers about three-quartersof the land area of UK, and ‘woodland’, which coversabout another 10%.

The purpose of the bird indicator was initially as atool to raise awareness. It has been one of the moresuccessful of the 15 headline indicators, proving tobe resonant both with the public and the media, andgenerating regular media interest. Having becomeestablished, the indicator was then used to set targetsand to monitor progress. The bird index demon-strates the potential power of indicators. It turns alarge amount of scientific data into a simple, under-standable and meaningful presentation. This in turnhas raised awareness and acted as a spur for researchand policy action.

A brief history of the wild bird indicator

The wild bird indicator was first developed between1997 and 1998 based on ideas proposed by the RoyalSociety for the Protection of Birds (RSPB) and WWFin an expert advisory group set up by the thenDepartment of Environment, Transport and theRegions (DETR). The intention was to develop andreview wildlife indicators to underpin the 1999 UKSustainable Development Strategy (Anon. 1998,1999).

This group identified a number of wildlife indica-tors reflecting conservation issues: the number andcondition of Sites of Special Scientific Interest, thenumber and status of priority species and habitatscovered by Biodiversity Action Plans, the propor-tions of species of threatened status, etc. However, akey gap was broader indicators reflecting the generalhealth of common and widespread wildlife in thecountryside. These were needed to complementthose indicators measuring the state of species andhabitats of particular conservation value. The birdindex was developed to meet part of this need. Thefirst ideas were based on the concept of combiningseries reflecting ‘distance from target’ for key speciesand habitats, at least exploring this idea for birds(Bibby 1999). The advantage of the distance to tar-get approach was it potentially enabled an index tobe constructed by combining different species ofanimals, plants, birds, etc., with measures of the stateof different habitats. Disadvantages included theneed for agreed targets, which in the past had provedextremely problematical, and the need for good

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The state of play of farmland birds

3

quality long-term trend data for a broad range ofspecies and habitats.

These ideas were developed by the RSPB, BritishTrust for Ornithology (BTO) and the former DETRto create an index that reflects similar trends withoutrequiring the need for targets for individual species.Birds were chosen for a number of reasons. First,they are regarded as good general indicators of thebroad state of wildlife in the countryside, becausethey are wide-ranging in habitat distribution andtend to be at or near the top of the food chain (Fur-ness & Greenwood 1993). Secondly, there are verygood historical data for bird population changessince the early 1960s. Thirdly, birds have consider-able public resonance and hence were thought to bea useful means for raising awareness for general bio-diversity issues. During the course of development,trends for groupings of birds associated with anumber of different habitats were examined, buttwo key groups, for farmland and woodland, wereidentified. These birds and their habitats are foundacross most of the UK countryside. For this reason,the bird indicator, which was first published in theGovernment’s consultation on the Headline indica-tors in 1998, focused on these two particular habitattypes (Anon. 1998). It was based on common (i.e.species having greater than 500 breeding pairs in theUK) native bird species. Species were classified tohabitat using Gibbons

et al

. (1993: their table 13).Rare breeding birds were excluded because they aremostly the focus of dedicated conservation actionand concentrated at a relatively small number ofsites, and not representative of the wider country-side. Following a positive response to the consulta-tion, this indicator was formally adopted by the UKGovernment as one of its new 15 Headline indica-tors of sustainable development (Anon. 1999). Sincethen both the former Ministry of Agriculture, Fish-eries and Food (now Department for Environment,Food and Rural Affairs – Defra) and the ForestryCommission have developed key targets and com-mitments to reverse the long-term decline in farm-land and woodland birds by 2020, and progressreviews are published regularly (Anon. 2002). Spe-cifically, Defra adopted a Public Service Agreement(PSA) target in 2002 to ‘Care for our living heritageand preserve natural diversity by reversing the long-term decline in the number of farmland birds by2020, as measured annually against underlying trends’.The publication of UK indicators has also encour-aged parallel development for individual countries ofthe UK and English regions (Anon. 2003a, 2003b).

An overview

Here we review the population trends and conserva-tion status of lowland farmland birds in the UK usingthe latest information available. We examine pat-terns among species and where possible identify thekey demographic stage that is acting to limit popu-lation growth. Next, we explore the populationdynamics of the subset of farmland species that formpart of the UK Government’s headline wild birdindicator and look at the behaviour of the compositeindicator itself. We look at the properties of thefarmland indicator and the delivery plan for farm-land bird recovery. Finally, we use a simple model ofpopulation growth to explore plausible scenarios offuture change with reference to the Government’starget to reverse the long-term decline in thenumber of farmland birds by 2020.

METHODS

For further details on: trend information, see Marchant

et al

. (1990), Crick

et al

. (2004), Raven

et al

. (2003),Gregory

et al

. (2003a) and Eaton

et al

. (2004); popu-lation status, see Gibbons

et al

. (1996) and Gregory

et al

. (2002); and indicator methods, see Gregory

et al

. (1999), (2003b) and Freeman

et al

. (2001).Trend information comes mainly from two large-scaleannual surveys – the BTO’s Common Birds Census,which ran from 1962 to 2000 (Marchant

et al

. 1990,Crick

et al

. 2004), and the BTO/Joint Nature Conserv-ancy Committee/RSPB Breeding Bird Survey (BBS),which started in 1994 (Raven

et al

. 2003). In brief,the farmland bird indicator is the mean index createdby combination of the constituent species’ trends ona geometric scale, so that a doubling of one species’index is balanced by the halving of another (Gregory

et al

. 1999, 2003b).

RESULTS

Population trends and conservation status of farmland birds

Population trends and conservation status of a widerange of species that live on lowland farmland aregiven in Table 1. Nine of the species in the farmlandbird indicator are Red-listed, based on populationdeclines in excess of 50% over the last 25 years (Gre-gory

et al

. 2002). Of the three species that declinedmost dramatically (> 85%), Corn Bunting and GreyPartridge have continued to decline steeply, whereas

4

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Table 1.

Population trends and conservation status of lowland farmland birds in the UK. Conservation concern listing = a measure ofpopulation status (Gregory

et al

. 2002). UKBAP = a priority species in the UK Biodiversity Action Plan. FBI = inclusion in the farmlandbird indicator. Long-term trends are for 1970–2001 and short-term trends for 1994–2002 unless otherwise stated.

SpeciesConservation concern listing UKBAP FBI

Trend 1970–2001 (%)

Trend 1994–2002 (%)

Kestrel

Falco tinnunculus

Amber No Yes

−

37

2

−

30Red-legged Partridge

Alectoris rufa

1

Green No No

−

24

+

21Grey Partridge

Perdix perdix

Red Yes Yes

−

86

−

18Pheasant

Phasianus colchicus

1

Green No No

+

45

2,3

+

16Corncrake

Crex crex

Red Yes No

+

14

4

+

27

13

Stone Curlew

Burhinus oedicnemus

Red Yes No

−

15

5

+

54

14

Lapwing

Vanellus vanellus

Amber No Yes

−

41

2

−

18Snipe

Gallinago gallinago

Amber No No

−

64

6

+

52Curlew

Numenius arquata

Amber No No

−

49

2

−

20Stock Dove

Columba oenas

Amber No Yes

+

87

2,3

+

15Woodpigeon

Columba palumbus

Green No Yes

+

87

7

+

5Turtle Dove

Streptopelia turtur

Red Yes Yes

−

77

−

42Cuckoo

Cuculus canorus

Amber No No

−

43

2

−

25

Tree Sparrows

Passer montanus

appear to be recov-ering – up by 55% since 1994. Of the five speciesexperiencing long-term declines of between 50 and85%, Turtle Dove

Streptopelia turtur

continues todecline steeply, three (Skylark, Yellowhammer andStarling) show moderate declines, and one (Linnet

Carduelis cannabina

) has been broadly stable since1994. The Yellowhammer appears better able toexploit cereal crops than other seed-eaters and itsdecline started later than most, in the 1980s (Brad-bury & Stoate 2000; Morris et al. 2001, 2002). TheReed Bunting Emberiza schoeniclus population hasdeclined by nearly 50% over the last 30 years but hasbeen stable since 1994. All three amber-listed spe-cies in the farmland bird indicator have shownalarmingly steep declines since 1994, 30% for Kes-trel Falco tinnunculus, 18% for Lapwing Vanellusvanellus and 14% for Yellow Wagtail Motacilla flava.Although not included in the indicator because ofthe lack of annual count data, the UK distribution ofBarn Owls Tyto alba declined between the twobreeding bird atlases by 39% (Gibbons et al. 1993).The latest population estimate was around 4000pairs in 1995–97, but comparison with earlier sur-veys is complicated by differences in the methods(Toms et al. 2001). A recently initiated annual mon-itoring programme should improve monitoring forthis species.

Seven species in the farmland bird indicator areincreasing (Table 1). For Greenfinch Carduelis chlo-ris and Goldfinch Carduelis carduelis, both long-term and short-term trends are positive, and

Whitethroats Sylvia communis have been increasingin numbers since the population crash in the late1960s. Three species (Jackdaw Corvus monedula,Woodpigeon Columba palumbus and Stock DoveColumba oenas) have almost doubled in populationsize since 1970, and all three species, as well as RookCorvus frugilegus (Marchant & Gregory 1999), con-tinue to increase or are stable in number.

The high profile of the farmland bird indicatorfocuses attention on its constituent 20 speciesdescribed above, but population trends in other low-land farmland species are also of interest. Barn Swal-low Hirundo rustica numbers have fluctuated overthe past few decades but are now moderatelyincreasing. Numbers of Carrion Crow Corvus coroneand Magpie Pica pica, like most other corvids, haveincreased steadily since the 1970s. Four rare species– Quail Coturnix coturnix, Corncrake Crex crex, CirlBunting and Stone Curlew – are Red-listed on thebasis of historical declines, but the latter three haveincreased considerably over the past decade inresponse to targeted conservation management(Aebischer et al. 2000b, Peach et al. 2001, Gregoryet al. 2003a; Eaton et al. 2004). Numbers of Quailare notoriously variable in the UK and the species isdifficult to census because it is so cryptic in the field.However, the Red-backed Shrike Lanius collurio,once a relatively widespread bird, is now virtuallyextinct in the UK. One introduced farmland species– the Red-legged Partridge Alectoris rufa – hasdeclined over the long-term but the current trend ispositive. Numbers of Little Owl Athene noctua and

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The state of play of farmland birds 5

Little Owl Athene noctua1 Green No No −5 +26Skylark Alauda arvensis Red Yes Yes −54 −14Swallow Hirundo rustica Amber No No +11 +10Meadow Pipit Anthus pratensis Amber No No −312 −5Yellow Wagtail Motacilla flava Amber No Yes −597 −14Pied Wagtail Motacilla alba Green No No +52 +23Wren Troglodytes troglodytes Green No No +548 +14Dunnock Prunella mudularis Amber No No −36 +13Robin Erithacus rubecula Green No No +43 +16Blackbird Turdus merula Green No No −19 +16Song Thrush Turdus philomelos Red Yes No −52 +13Lesser Whitetrhoat Sylvia curruca Green No No +2 −27Whitethroat Sylvia communis Green No Yes −189 +30Spotted Flycatcher Muscicapa striata Red Yes No −82 −42Great Tit Parus major Green No No +51 +19Red-backed Shrike Lanius collurio Red Yes No −9010 Extinct?15

Magpie Pica pica Green No No +109 +2Jackdaw Corvus monedula Green No Yes +83 +12Rook Corvus frugilegus Green No Yes +4011 0Carrion Crow Corvus corone Green No No +84 +15Starling Sturnus vulgaris Red No Yes −662 −13House Sparrow Passer domesticus Red No No −657,12 −7Tree Sparrow Passer montanus Red Yes Yes −94 2 +55Chaffinch Fringilla coelebs Green No No +29 −5Greenfinch Carduelis chloris Green No Yes +22 +31Goldfinch Carduelis carduelis Green No Yes +35 +18Linnet Carduelis cannabina Red Yes Yes −51 −4Bullfinch Pyrrhula pyrrhula Red Yes No −57 −26Yellowhammer Emberiza citrinella Red No Yes −52 −13Cirl Bunting Emberiza cirlus Red Yes No +11912 +54Reed Bunting Emberiza schoeniclus Red Yes Yes −48 +3Corn Bunting Miliaria calandra Red Yes Yes −897 −41

Data are derived from Common Bird Census (CBC) plots from 1966 up to 2000 (except where indicated) and Breeding Bird Survey (BBS)plots from 1994 to 2002. For long-term trends, counts were modelled using a full site by year log-linear Poisson regression model withpost hoc smoothing of the annual indices. Reported long-term population changes are the differences in smoothed annual indices injoint CBC–BBS models from 1970 to 2001 – the year prior to the last available data, except for House Sparrow (from 1976). All figuresrefer to the UK. However, for species where there is evidence of substantial and statistically significant differences in trends within andoutside England, the overall trends are based solely on the CBC prior to 1994 and solely on the BBS from 1974 to 2002. Caveats relatedto unrepresentative habitat coverage, small sample sizes or fluctuating populations are listed. Short-term trends were derived fromcounts on BBS squares analysed using a full site by year log-linear Poisson regression model, and cover the period 1994–2002.1Species introduced into the UK.2The trend during the period covered solely by the CBC (prior to 1994) may be unrepresentative of the UK due to geographical or habitat-related bias towards populations with low densities.3Long-term trend may be biased by differences in BBS and CBC methodologies.41970–2003, RSPB.51970–2000, RSPB.61974–1999 Common Birds Census, Gregory et al. (2002).7Small sample size during some part of the survey period.8The species shows large natural fluctuations from year to year.9The population has not recovered from the 1968/69 crash caused by severe drought on the African Sahel wintering grounds.101973–77 to 1995–99. Rare Breeding Birds Panel, Gregory et al. (2002).111975–77 to 1996. Rookeries Census, Marchant and Gregory (1999).121976–2001.131997–2003, RSPB.141995–2000, RSPB.15Effectively extinct as a breeding species; last confirmed breeding in 1999.

SpeciesConservation concern listing UKBAP FBI

Trend 1970–2001 (%)

Trend 1994–2002 (%)

Table 1. Continued

6 R. D. Gregory, D. G. Noble & J. Custance

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Pheasant Phasianus colchicus (both introduced intothe UK) have also been broadly stable over the longterm and increasing in the short term (Table 1).

A number of species occur widely on farmland butprefer other habitats. Highly abundant in hedgerowsand wooded areas of farmland, numbers of WrenTroglodytes troglodytes, Dunnock Prunella modularis,Robin Erithacus rubecula, Great Tit Parus major andChaffinch Fringilla coelebs show positive long-termand short-term trends (Table 1). The Lesser White-throat Sylvia curruca is also associated with hedge-rows and although its long-term trend is stable, ithas shown a sharp decline since 1994. After signific-ant declines between the 1970s and 1990s, Black-bird Turdus merula and the Red-listed Song ThrushTurdus philomelos are currently showing signs of arecovery. However, the Red-listed Bullfinch Pyr-rhula pyrrhula and Spotted Flycatcher Muscicapastriata are continuing to decline steeply. In additionto Lapwing, two other waders – Curlew Numeniusarquata and Snipe Gallinago gallinago – breed widelyon farmland, mainly in upland or lowland wet grass-land habitats (Wilson et al. 2004). A recent surveyrevealed that Snipe declined by more than 60% andCurlew by about 40% on lowland wet grasslands inEngland and Wales since the early 1980s (Wilsonet al. in press), although this habitat caters for onlypart of their populations. Curlew has declined inabundance since 1994 whereas Snipe appear to haveincreased following longer-term decline. Amongbirds of open countryside, Pied Wagtail Motacillaalba numbers have increased whereas Meadow PipitAnthus pratensis shows a moderate decline. Althoughlargely an urban bird, House Sparrows Passer domes-ticus are commonly found on farmland associatedwith buildings. This recently Red-listed species hasdeclined steeply (65%) since 1976 and continues toexperience a much-publicized fall in numbers.

Dividing the farmland indicator species into theseven species that have increased since 1970, andthe 12 that have shown major declines (followingthe PSA delivery plan), is instructive (Fig. 1). Theincreasing species (Fig. 1a) can be subdivided intothose that have increased over the whole period(four species that have increased by around 2% perannum) and those that declined but have then shownsome recovery (three species that have increased byaround 3% per annum since 1985). The patternsamong the declining group of species are moresimilar (Fig. 1b), although there are signs of flatten-ing and even upturn in the trends for some speciesin recent years; overall declines range from 2 to 10%

per annum from moderate to severe decline amongthese species.

Taking this group of lowland farmland birds as awhole (and it is not an exhaustive or definitive list),58% of them have shown long-term declines (> 10%)and 32% short-term declines (> 10%: Table 1).

Demographic causes of decline

Two sources of information have helped to shed lighton the key demographic processes in populationchanges in lowland farmland birds in the UK: (i)integrated population modelling of survey, nestrecord scheme and ringing scheme data, and (ii)intensive autecological studies. Survival, as opposedto productivity, is implicated as the key factor in thepopulation declines of seed-eating passerines, suchas Cirl Bunting (Evans & Smith 1994) Reed Bunting(Peach et al. 1999), House Sparrow and Goldfinch(Siriwardena et al. 1999, Hole et al. 2002). It is alsobelieved to be a contributing factor in the declines ofCorn Bunting (Donald & Evans 1994, Donald &Aebischer 1997), Yellowhammer (Kyrkos 1997) andTree Sparrow (Crick et al. 2004). However, forLinnet, the trend appears to be driven by reducedbreeding performance (Siriwardena et al. 2000).Survival is also considered the main factor in thedecline in Starlings (Freeman et al. 2002). The roleof survival on population trends for Skylark (anotherspecies that feeds on seeds during the winter) is notclear, but the shorter breeding season resulting fromchanges in cropping regimes is believed to have amajor role (Chamberlain & Crick 1999, Donald &Vickery 2001). A reduction in the number of breed-ing attempts is also thought to be driving the declinein Turtle Doves (Browne & Aebischer 2001). Agri-cultural practices during the breeding season areknown to have adverse effects on the breeding per-formance of Corn Buntings (Brickle et al. 2000),Grey Partridge (Potts 1986), Stone Curlew (Aebischeret al. 2000b), Lapwing (Shrub 1990) and Corn-crake (Green & Stowe 1993). It should be noted thatthe number of nesting attempts made per season isnot provided by the nest record scheme, and it may bea crucial variable for some species. Among increasingfarmland species, improved breeding performance isthought to have driven increases in Stock Dove(O’Connor & Mead 1984) and Jackdaw (Gregory& Marchant 1996), whereas trends for long-distancemigrants such as Common Whitethroat and BarnSwallow appear to be influenced most strongly bysurvival (Baillie & Peach 1992).

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The state of play of farmland birds 7

Figure 1. Individual trends of the 20 farmland species included within the UK farmland bird indicator: a group of (a) seven ‘increasing’and (b) 12 ‘declining’ species as defined within the PSA delivery plan. There are no annual data for Barn Owl.

8 R. D. Gregory, D. G. Noble & J. Custance

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Patterns of trend in the farmland bird indicator

The indicator shows separate trends for ‘all commonspecies’, ‘woodland’ and ‘farmland’ species (Gregoryet al. 1999, 2003b, Freeman et al. 2001; Fig. 2a). Thefarmland bird index has fallen by 42% from 1970 to2002; specialist farmland birds have declined by58%, while generalists have increased by 4% from1970 to 2002 (Fig. 2b). There is, however, a gooddeal of variation in the pattern of trends when we

categorize birds simply as generalist or specialist.Population declines among farmland birds weremost marked from the mid-1970s to the 1990s witha suggestion of a lessening of declines in the last dec-ade. The farmland indicator trend is well describedby a simple model in which an initial increase upuntil 1977 is followed by a 5% and then a 1% perannum decrease (Fig. 3). This supports the view thatthe rate of decline has lessened. The statistical testsunderlying the PSA targets reinforce this importantconclusion (see Fig. 4 below).

DISCUSSION

The farmland bird indicator

The wild bird indicator describes the trends of com-mon species drawing on a range of surveys (Gregoryet al. 1999, 2003b). It is a composite indicator, i.e. itis based on a ‘basket’ of species and reflects the aver-age behaviour of the constituent species. The speciesare weighted equally, so that trends in, for example,Woodpigeon count the same as those in Corn Bunting.We have resisted weighting the indices by populationsize or conservation status because each would leadthe indicator in a particular direction. The first wouldcreate an indicator dominated by the most abundantbird species, the second by those species judged to bemost threatened and thus not by the full suite of speciespresent in farmland. Neither approach would seemappropriate given the role of this indicator.

To reiterate, the purpose of the indicator is as abarometer of broad-scale change in the countrysideand as a surrogate for changes in other wildlife. Birds

Figure 2. The UK Government’s headline wildlife indicator –(a) populations of wild birds and (b) the farmland bird indicatorsplit into generalist and specialist farmland species.

Figure 3. The farmland bird indicator with modelled rates ofdecline at 5% per annum from 1977 to 1988 and 1% per annumfrom 1988 to 2002.

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The state of play of farmland birds 9

can be good indicators because they often reflectchanges in the state of other animal and plant popu-lations (Furness & Greenwood 1993). There is, forexample, evidence to show that farmland bird declinesare concomitant with those in insect and plant popu-lations probably driven by a common factor, the inten-sification of agricultural production (Rands &Sotherton 1986; Donald 1998, Sotherton & Self2000, Benton et al. 2002). Such indicators, however,must be used with care as a guide to changes in thewider environment. There are potentially a numberof complex causes of changes in bird numbers andhence in the indicator, such as food, habitat condi-tion, predators, disease and competition. Cold win-ter weather has a significant short-term impact onsusceptible bird populations and thus on the indica-tor from year to year, but weather does not appear todrive the overall trend. There is a positive correlationbetween the annual change in the farmland index andthe Central England Temperature in the precedingwinter (r2 = 0.42, P = 0.001). A small number of thespecies in the farmland index may also be affected byconditions on their migration and wintering groundsin Europe and Africa (Baillie & Peach 1992).

Delivering farmland bird recovery

The Government’s PSA target aims to ‘Care for ourliving heritage and preserve natural diversity … byreversing the long-term decline in the number offarmland birds by 2020, as measured annually againstunderlying trends’. With this target is a detaileddelivery plan that defines how the target is measuredand how it will be achieved. The target is measuredagainst a modified version of the farmland bird index:the trend line is ‘smoothed’ to remove sampling errorand short-term peaks and troughs due to weather(Freeman et al. 2001) and only data collected fromwithin England are used – the PSA target was adoptedby Defra, whose land management schemes and otherpolicies apply only in England. The target is judgedto have been achieved when the trend in the index andthe associated lower confidence limit (using 95% CLs)are both positive. The smoothed version of the farm-land bird index reveals the underlying trend (Fig. 4a)and by showing the proportional change in this indexfrom year to year, we are able to measure progress(Fig. 4b). The recent upward trend in the index isencouraging (Fig. 4b), but there is some way to gobefore there is a statistically significant increase. Thedelivery plan recognizes that the statistical target isachievable in various ways, some of which might be

judged undesirable. Meeting the statistical test alonewould not be sufficient to have delivered the overalltarget. For example, the statistical test could in theorybe met by increases among a few highly abundantgeneralist species, while specialists continued to belost (see below). The vision within the plan is to havestable or rising populations of the 20 key farmlandbirds. The Government’s aim is to bring each speciesinto a stable or increasing position and to safeguardand sustain that achievement.

What does the future hold?

Having described the historical pattern of popu-lation trends among farmland birds, we can alsolook forward. With a range of policy initiatives inplace, there is room for optimism, but what sort ofoutcomes might we expect from what we know aboutfarmland birds? We have looked at this question bymodelling trends in the overall indicator and then byseparately considering trends among the ‘increasing’(n = 7) and ‘declining’ (n = 12) group of species in

Figure 4. (a) A smoothed version of the farmland bird indicatorfor England with 95% confidence limits derived by bootstrap(dashed lines). (b) The smoothed English farmland bird indexpresented as a proportion of the previous year’s index with 95%CLs on the proportional change. Values > 1.0 indicate increaseand < 1.0 indicate decrease between years.

10 R. D. Gregory, D. G. Noble & J. Custance

© 2004 British Ornithologists’ Union, Ibis, 146 (Suppl. 2), 1–13

Figure 5. Modelling future scenarios of population change among the farmland birds within the indicator from 2002 (marked by an arrow)to 2020. (a) Overall change in the farmland indicator with average population increases of 1, 2, 3 and 4% per annum. In parts b–f, the‘increasing’ species are represented by filled symbols, ‘declining’ species by open symbols, and farmland bird index by a line. (b)Increases of 1% per annum among all the ‘increasing’ (top line) and ‘decreasing’ species (bottom line) – the overall change in the farmlandbird index is +20% 2002–2020 (middle line). (c) Increases of 3% per annum among all the ‘increasing’ (top line) and ‘decreasing’ species(bottom line) – the overall change in the farmland bird index is +70% 2002–2020 (middle line). (d) Stability among the ‘increasing’ species(top line) and increases of 1% per annum among the ‘decreasing’ group of species (bottom line) – the overall change in the farmland birdindex is +12% 2002–2020 (middle line). (e) Stability among the ‘increasing’ species (top line) and increases of 1% per annum amongnine and decreases of 3% per annum among three of the ‘decreasing’ species (bottom line) – the overall change in the farmland bird indexis 0% 2002–2020 (middle line). (f) Increases of 3% per annum among the ‘increasing’ species (top line) and decreases of 1% per annumamong the ‘decreasing’ group of species (bottom line) – the overall change in the farmland bird index is +9% 2002–2020 (middle line).

© 2004 British Ornithologists’ Union, Ibis, 146 (Suppl. 2), 1–13

The state of play of farmland birds 11

the farmland bird index. This is a simple model withconstant rates of change and no formal testing of tar-gets, but the results are revealing. It is obvious thatany positive and sustained average increase in theconstituent trends of the farmland indicator willmove us towards the PSA target (Fig. 5a). Interest-ingly, an average increase of 3% per annum, which ishigh but realistic, brings the farmland bird indexback to its value in 1970 by 2020.

Similarly, if we model the fate of the ‘increasing’ and‘declining’ species separately, average increases of 1%and 3% per annum hold the potential of deliveringthe farmland bird target by 2020 (Fig. 5b,c), althoughthis would need to be confirmed by examining theconfidence limits around these trends. Even if modestincreases of 1% per annum were restricted to the declin-ing species group, there is still a realistic chance ofapproaching the farmland bird target by 2020 (Fig. 5d).It is, however, probably unrealistic to assume that eachspecies will respond in the same positive way to policymechanisms and other drivers, and if only a smallnumber of declining species falter, the PSA target maynot be met (Fig. 5e). Declines in as few as two or threespecies could jeopardize a positive outcome. A furtherkind of undesirable outcome would come about ifpopulation increases in the increasing group stronglyoutweighed population declines among the declininggroup. For example, the overall decline in the farmlandbird index could be reversed by an upsurge in the‘increasing’ species alone while the ‘declining’ speciescontinued to fall in number (Fig. 5f ). This would notbe judged sufficient to meet the PSA target, whichaims to bring each species into a stable or increasingposition. Our analysis shows that delivery of the PSAtarget will depend on the complex behaviour of the con-stituent species trends, and critically on reversing thetrends among the suite of declining farmland species.

We would like to thank David Gibbons, Mark Avery, AndyEvans, Juliet Vickery, Phil Grice, John Osmond, RockyHarris, Mark Eaton, Richard Bradbury and Simon Wotton.We also thank the two referees for constructive comments.

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