A Review of Thirty-five Years of Osprey (Pandion haliaetus)

Nesting Data in Rhode Island

By

Eric S. Walsh

A MAJOR PAPER SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIRMENTS FOR THE DEGREE OF MASTER OF ENVIRONMENTAL SCIENCE AND MANAGEMENT

UNIVERSITY OF RHODE ISLAND

JULY 30, 2013

MAJOR PAPER ADVISOR: Dr. Peter Paton

MESM TRACK: Conservation Biology

Photo by David Windsor

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Introduction

The osprey (Pandion haliaetus) is one of North America’s most magnificent,

recognizable, and unique birds of prey. They are a pandemic species, found on every continent

except Antarctica and inhabit both inland and coastal regions in the breeding and non-breeding

season. In North America, most ospreys are migratory breeding from Florida north through

Newfoundland and west through Canada and southern Alaska and then south through the west

coast and sections of Montana, Idaho, Wyoming, Colorado, Arizona, and Utah (Henny et al.

2010). In New England, they breed along the south coast of Connecticut east to Massachusetts

and north along the coast. They are also found along inland lakes and streams in Maine, New

Hampshire, and Vermont. RI’s breeding population are present between April and August and

are located predominantly along the south coast and throughout Narragansett Bay.

They are taxonomically unique being in a monotypic genus Pandion and family

Pandionidae. Their closest relatives are from the class Accipitiforms, which includes eagles and

kites. They are piscivores foraging almost exclusively on a diet of fish (Poole 1989) in shallow

tidal zones along the coast (Prevost 1979) and clear shallow freshwater bodies (Vana-Miller

1987). They do not generally discriminate among fish species when foraging (Hughes 1983)

except probably being more successful targeting slower benthic species (Flemming and Smith

1990) than picsivorous species that are more weary (Vana-Miller 1987).

Prior to the use of DDT ospreys were common up and down the eastern seaboard. In the

1950’s-60’s, the osprey’s population began to decline because of the use of organochlorine

pesticides (Ames 1966). DDT accumulates up the food chain, eventually reaching birds of prey

causing thin eggshells resulting in breakage during incubation and ultimately nesting failure

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(Wiemeyer et al. 1975). In the 1940’s, breeding surveys estimated ~1000 nests between New

York and Boston. By the end of the 60’s, nest sites declined by 98.5% to 150 active nests

(Spitzer & Poole 1980). In 1972, the Federal Government banned DDT, and then in 1976, the

osprey was listed as an Endangered Species by the U.S. Fish and Wildlife Service. Since then,

the osprey began to recover and was up-graded to “Threatened” in 1982 and “Special Concern”

in 1999. Today, the IUCN list the osprey as Least Concern. In the United States, ospreys have

recovered to 16,000-19,000 breeding pairs in 2001, and they have been proposed as a sentinel

species for contaminate investigations because they fit the criteria well (Henny et al. 2010).

Many conservation recovery programs and citizen monitoring programs focus their

attention on monitoring and managing osprey populations because of their previous sharp

decline. In 1977, the Rhode Island Department of Environmental Management (RIDEM) began

monitoring the state’s osprey population as it recovered from the effects of DDT. Staff biologists

and volunteers observed all known nests in Rhode Island and recorded how many chicks fledged

each year. In 2010, with cooperation from RIDEM, the Audubon Society of Rhode Island

(ASRI) assumed management of this successful program. In 1977, there were 12 Active nest

sites and 7 successful nests compared to 2012 with 126 Active nests, and 96 successful nests

(unpublished ASRI data).

Osprey population recovery has been associated with nest structure type and availability

(Reese 1977, Henny and Kaiser 1996), habitat suitability (Toschik et al. 2006), contaminate

concentrations (Henny et al. 1977, Toschik et al. 2006), food resource availability (Poole 1982,

Eriksson 1986), proximity to conspecific nesters (Toschik et al. 2006), and human activity

(Levenson and Koplin 1984). North Atlantic coastal populations have recovered at variable rates

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(Henny et al. 1977, Spitzer and Poole 1977) exhibiting variable reproductive rates over time and

space (Henny et al. 2010).

Historically, they nest on coniferous and deciduous tall dead trees (Berger & Mueller,

1969) or live trees (MacCarter 1972), utility poles (Prevost 1977), cellular towers, and artificial

nesting platforms (Newton 1980). Within heterogeneous landscapes, nest site locations have

been found to change over time (Bai et al. 2009) and the effects of landscape context on nest

success is varied (Swenson 1981, Lohmus 2001). They typically choose sites with an

unobstructed view of the surrounding landscape (Van Daele & Van Daele 1982). Coastal

populations usually nest close to foraging resources along shallow tidal wetlands. Inland

populations will typically nest and subsequently travel 3-5 km (Vana-Miller 1987, Poole 1989)

to forage at shallow water bodies and as much as 14 km if necessary (Hagan and Walters 1990).

Artificial nesting structures often provide access to nesting habitat that would otherwise not be

suitable for nesting (Newton 1980). These structures are usually placed in open saltwater

marshes allowing for close proximity to forgaing ground with an open unobstructed view.

The RI osprey breeding data has not been fully analyzed. In the past, only nest status

metrics and reproductive rates have been reported. Little was known about the location of nest

sites within the Rhode Island landscape and their change over time. Until recently, the structure

types were unknown for Rhode Island’s breeding population. Subsequently the relationship

between structure type and breeding success in Rhode Island had not been explored.

The objective of this paper was to review the Rhode Island osprey nesting data between

1977 and 2012 and describe the observed trends. The second objective was to identify areas of

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research opportunity or additional analyses that will provide insight into the dynamics of a

population that repopulated a landscape after a population bottleneck.

Methods

Database and Monitoring

All analyses were conducted on a data set collected in the State of Rhode Island from

1977 to 2012. Each year volunteers would monitor each known osprey nest site between April

and July, documenting the status of the nest sites each month and the number of young observed.

The Rhode Island Department of Environmental Management (DEM) originally implemented

the nest-monitoring program until 2008. In 2009, the program was transferred to the Audubon

Society of Rhode Island (ASRI), which implemented data collection in 2010. Subsequently,

there are no data for nesting season 2009.

The data for each year consisted of the status of each nest and the number of fledglings

produced for each successful nest. Each year every nest was categorized as one of the following:

Inactive, Subadult/Housekeeping (starting in 2010 nest sites that showed signs of osprey activity

but not nesting behavior such as incubation posture, were labeled as Housekeeping instead of

Subadult to align with the prevailing evidence that not all nest sites with non-incubating pairs are

necessarily Subadults), Active, and Successful. Active sites were nests that showed signs of

nesting or young rearing, but failed to produce fledglings. Nest sites were identified based on

passive discovery of active sites. Potential nest sites were monitored after a report was made of

the possibility of an active nesting pair. There was no active effort to identify nest sites around

the state.

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The original data I used were in three forms. The first was a spreadsheet with nest names

and nesting history for nest sites between 1977 and 2008. The second was a summary of each

year’s nest status between 1977-2012, which included the number of Inactive, Subadult, Active,

Successful nest sites, and Fledglings with calculations for the number of fledglings per Active

and Successful nest site. The third form was a GIS database that contained the spatial location of

most nest sites and the status of each site for each monitored year. The nesting history data in the

GIS originated from the spreadsheet data. However, the first database did not correspond

perfectly to the GIS records because not every nest site was in the GIS. The reason was

unknown; therefore, the analyses were conducted on the GIS data and the results do not perfectly

correspond to the original summary data published by the DEM and ASRI.

Data QA

In an effort to improve the spatial information of each monitored nest site, the Audubon

Society of Rhode Island hired three interns for the 2012 nesting season to record the spatial

location and structure type of every monitored site in 2012 (N=200). All nest sites being

monitored in 2012 were visited, as a result, there were nests (N=64) used in these analyses,

which spatial and platform type were not explicitly confirmed.

To improve the accuracy of the data, I investigated the discrepancies for each year where

the GIS summary did not align with the summary data. For several of the monitored years, there

were DEM published osprey newsletters that contained individual nest data. When possible, I

cross-referenced the published and spreadsheet data with the GIS data. However, it was not

possible to assess every nest because in several instances, nest names were not consistent

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through the years, and there was no available information to trace nest name changes. I used the

newsletters first and then the spreadsheet when correcting the GIS data.

Data Analysis

I summarized the data to provide insight into nesting trends between 1977 and 2012. I

analyzed the average distance between nest sites using a Hawth’s Tools Euclidean distance

calculation in ArcGis 9.3. I analyzed the difference between structure type and fledgling

production using an ANOVA with significance of α<0.05. I analyzed the landscape changes

between years using 1972, 1985, 1999, and 2010 30 m resolution Landsat imagery already

categorized into 12 land cover types for the state of Rhode Island. The 12 cover types were

primarily focused on natural land cover with only two broad categories related to human land use

(Agriculture and Urban). I ran the models with only the land cover types that presumably would

affect osprey nesting. The following types were omitted: coastal sandy areas, barren, urban grass,

and brushland. Only non-coastal features and Rhode Island land cover were classified in the

imagery. As a result, buffers that encompassed coastal water or parts of Massachusetts and

Connecticut contained no data. I was unable to locate land cover data for these states dating back

to the 1970’s and 1980’s. To account for the potential bias and include coastal waters, I

calculated the percent area of the buffer zones that included the neighboring states and coastal

waters. I reported the coastal water percent area; the neighboring state area was negligible.

I used a 3 km buffer around each nest site to analyze the land cover directly associated

with each nest site. Since ospreys typically forage within 3-5 km of their nest sites, I selected a 3

km buffer, because I assumed the abundance of shallow open water was great enough that it was

unlikely an Osprey would have to travel further than 3 km to locate a food resource. I divided

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monitored years (1977-2012) into four cohorts and associated each cohort to an imagery year

(Table 1). I used ArcGIS 9.3 to process the imagery and produce the buffer zone rasters.

The buffer zone and entire state LULC imagery were analyzed using Fragstats 4.1

(McGarigal 2012). I analyzed the entire state’s land cover to compare the distribution of cover

types within the buffer zone to cover types over the entire state. I report percent land cover of the

selected cover types.

Results

The Osprey population has increased 10.27 fold from 11 Active nest sites in 1977 to 124

Active sites in 2012, of the 124 Active sites in 2012, 94 were successful (Figure 1). The number

of fledglings produced each year has increased from 10 in 1977 to 164 in 2012 (Figure 2). The

success rate or average number of fledglings per successful nest has ranged from 2.7-1.5 with an

average of 1.9(SD=+/- 0.2) fledglings per year (Figure 3). There was no detectable change in the

overall percent change in the number of fledglings produced from year to year (average=11.6%

SD=+/-28.4%). The reproductive rate has ranged from 0.9 to 1.8 and has averaged 1.4 (+/-0.3)

(Figure 4). The reproductive rate is based on the number of fledglings per active nest; it is lower

than the success rate and is a measure of the health of a population.

The ospreys have built their nests on a variety of structures. There are eight primary

structure types; these include platform, telephone, cell, tree, other, channel. A platform is any

manmade structure specifically erected with the intent to support an osprey nesting pair. Usually,

these platforms are approximately 10’-14’ tall (this category also includes telephone poles that

are intentionally erected as osprey nest platforms) and located in marsh habitat or in close

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proximity to foraging habitat. The telephone category represents manmade structures that are not

intentionally erected for osprey breeding, but are subsequently used as a nest site. This category

includes high-tension electric poles and telephone poles. Nest sites built on light poles are in the

structure category Light. The light category is for any structure that has a light or set of lights at

the top, such as athletic field lights. The cell category is for nests built on cell phone towers and

the channel category is for the few nest sites built on channel markers. The tree sites are in the

tree category, and finally the other category is for all sites that do not fit into any of the other

categories. For example, a nest built on a water tower would be classified as other.

Between 1977 and 2012 of the known structure types, 37% of the nest sites were built on

platforms, 20% on telephone poles, 11% on light poles, 8% on cell phone towers, and 6% on

trees. Between 1977 and 1989, the predominate structure type was telephone poles, but after

1987, platform structures increased in use from 7 - 54 structures, an 87% increase (Figure 5).

Cell towers were the second greatest used structure in 2012 with 24, which was the last known

year of a steady increase in Cell tower use that began 2008 with 10 towers.

Platforms produced an average of 1.43 fledglings while cell towers produced 1.64 per

year, the greatest average number of fledglings. Telephone poles produced an average of 1.35

fledglings per year and trees 1.53 (Figure 6). There was a significant difference between yearly

fledgling production F(34,1308), p= <0.001. However, there was no significant difference in

fledgling production between structure types F(4,1308) =1.47, p=0.21 and there was no

interaction effect between year and structure F(120, 1308)=0.93, p=0.68.

Of the Active nest sites on cell towers, an average of 91.1% were successful, platforms

had a success rate of 73%, telephone poles a 76%, and trees 78.4% (Figure 7). There was a

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significant difference between structure success rates F(6,194)=3.76, p=0.001. A Post Hoc

Tukey test showed that the differences were between platforms and cell towers (padj=0.02), and

unknown and cell towers (padj<0.001). There was a change in the success rates of platforms, cell

towers, and telephone poles (Figure 7, 8, 9). Cell towers appear to be declining in success rate,

because between 1984 and 1998 the rate was 100% but since then the rate has fluctuated between

100% and 50% with the most recent rate in 2012 at 72%. Telephone and platforms were more

variable in the early years with a range of 100%-0% and 100%-25% respectively in the first 10

years. In the last 10 years, telephone poles and platforms have fluctuated between 100%-61%

and 96%-75% respectively.

The average distance between nest sites has decreased since 1977 to 2012 from ~7000

meters to ~1700 meters. There were groups of years where the average distance decreased (1978-

1981, 1989-1992, and 2007-2012) followed by intervening years of fluctuations in the average

distance (Figure 11).

The landscape within 3 km of nest sites changed between 1977 and 2012. The observed

changes represent two types of changes. The first is a change in the overall composition of the

Rhode Island landscape (Figure 12), and the second is a change in the location of nest sites

within the landscape (Figure 13). The first change was observed in deciduous forest and

coniferous forest. Between 1977 and 2012, the overall deciduous forest cover had changed from

51.8% to 24.1%, a decrease of 27.6%. In 1977, nest sites had approximately 46.1% deciduous

forest within 3 km and by 2012 nest sites were located within landscapes with 18.5% deciduous

forest cover, a decrease of 27.6%. Coniferous forest showed similar shifts, the nest site cover

increased by 3% and the overall landscape cover increased by 2.8%. The second type of land

cover change was observed in urban land cover. Nest site urban land cover within 3 km

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increased from 10% to 29% in 1977 to 2012 respectively. During this same period, overall urban

land cover increased from 13% to 22%. Another land cover shift is open water. Open water

comprised 5.9% of the total area within 3 km of the nest sites, while 4.3% of the total landscape.

The amount of open water within the buffer zones decreased to 4.3% in 2012 and the total

landscape had 4.2% open water. There was an overall decrease in the percent cover of deciduous

wetlands, mixed forest, herbaceous wetlands, and open water and overall increase in urban land

cover that exceeded expected changes given the proportion of each in the entire landscape (Table

2). Overall nest sites were located within landscapes with more deciduous wetlands, herbaceous

wetlands, and urban land cover and less coniferous forest, mixed forest, and deciduous forest

then would be expected given the overall landscape distribution (Table 3).

Discussion

The Rhode Island osprey population is recovering from the observed decline in the

1950’s and 60’s caused by organochlorine pesticides. The recovery has shown yearly

fluctuations in Active and Successful nests with the two being closely synchronous within most

years. The exception was between 1988 and 1994 when the number of Active nests increased

from 23 to 43, a 47% increase but Successful nests increased from 19 to 26 a 27% increase. The

influx of breeding ospreys grew faster than the production of young. In addition, between 1988

and 1994, the average number of fledglings produced per successful nest decreased from 2.2 in

1988 to 1.7 in 1994. Interestingly, 2.2 was the highest the fledgling/successful nest rate has been

to date. If fledglings per successful nest rate did not decrease over the same period, then the

cause of a pair not producing at least one fledgling would be independent of the entire

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population’s ability to produce young. Since the evidence shows the entire population declined in

fledgling production, it leads to the possibility that there were environmental or density

dependent deterministic events driving the decline. A possible reason for this pattern was the

inability of the fish stock to support the foraging needs of the breeding population (Van Daele &

Van Daele 1982). At this time, I did not have fish stock data to test this theory. Another

possibility is the increase or influx of young naïve nesting pairs with little experience.

The pattern of slow successful nest growth in comparison to active nest growth would

eventually produce a depression or decline in active nest sites when the young nesting cohorts

from the depressed successful years reached breeding age. Ospreys reach sexual maturity at age

three to four (Poole 1989), so the 1988 cohort of young would have been at breeding age in

1991. The Active nest numbers did not decline in 1991, to the contrary they continued to

increase for three more years. This is a possible indication that the Active nest numbers were

increasing do to an influx of naïve nesters from outside of the Rhode Island breeding population.

Further supporting the naïve nester theory was the fledgling per successful nest rate. New nesting

pairs are not as successful as mature nesting pairs (Poole 1989). Since the 1988 to 1994 rate

decreased from 2.2 to 1.7 (Figure 3), then the slow growth in Successful nests may have been a

function of a young population and not a depressed fish stock.

The synchronous pattern between Active and Successful nests should be looked at with

caution though. Active sites are a measure of previous years’ success rate as an Active nest is an

indication of the start of nesting. Success is a representation of within year factors affecting

nesting. A depressed success rate is an indication of environmental factors affecting within year

fledgling production leading to an effect on active nest rates in the future. Between 2000 and

2002, the number of active nests increased from 56 to 87. In 1997, the number of successful

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nests was 37 and in 1999, the number of successful nests increased to 54. The young from 1997

would correspond to the breeding cohort of 2000 and 1999 would correspond to 2002. Hence, an

increase in successful nests produces an increase in breeding adults three years later (Figure 1).

The reproductive rate or average fledgling per Active nest site fluctuated over 35 years

between the highest at 1.8 in 1983, 1988, and 2000 to its lowest point in 1977 and 1981 at 0.9.

The rate was always above the critical replacement rate of 0.8 (Spitzer and Poole 1980) and in

comparison to populations in the Chesapeake Bay area and west in Idaho, Rhode Island’s was

more robust (Van Daele & Van Daele 1982, Watts and Paxton 2007). However, populations in

Europe have shown reproductive rates as high as 2.04 (Saurola 2005). There appears to be no

pattern in relation to the successful nest rate. The reproductive rate is an indication of the

population’s ability to produce young within an area. This number is affected by environmental

stochastity, deterministic events, and breeder’s maturity. The breeding population on average has

not increased its fledgling production from year to year; the percent change in fledgling

production has varied above and below zero (Figure 14). The increase in fledglings observed in

Figure 2 is a function of the increase in population size and not the environments ability to

support an increase in the production of young.

Structure

Ospreys in Rhode Island preferred to nest on platforms almost twice as often as any other

structure (Figure 15). Platforms also supported the greatest number of successful nest sites

(Figure 16). Platforms historically are located in and along coastal wetlands (Figure 17). In

Rhode Island, this would be the prime habitat for nesting, providing the ospreys with access to

extensive areas of shallow water. Among all structure types, platform use showed the greatest

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increase and at the greatest rate (Figure 5). Between 2002 and 2012, platform use increased at a

rate of 2.3 per year, the next closest was cell towers and telephone poles at 0.6 per year. There

was a statistically significant difference between the average number of successful platform and

cell tower nest sites. On average, cell towers produced more successful nests than platforms, but

this may be shifting. The percentage of successful nests on cell structures appears to be

decreasing while the percentage of successful platform and telephone nests are increasing

(Figure 7, 8, 9). However, the observed cell tower pattern may be a function of small sample

size, between 1984 and 1997only one tower was active and successful. Compared to 2012, 23

cell towers were active. Across all structures, there was no difference in fledgling production.

This is different from other osprey populations that produced more offspring on artificial

structures (Van Daele & Van Daele 1982). The lack of difference is an indication that the

structure and any correlations with structure types, i.e. location (since each structure type would

be within a specific landscape type) has no significant affect on reproductive rates. Open coastal

waters accounted for 22% of the area within 3 km of nest sites and this value was relatively

consistent through the years (Figure 18). One theory is the close proximity to and vast expanse of

available foraging habitat negates any difference in fledgling production that might occur

because of differences in structure type. These analyses did not quantify the average land cover

type surrounding a structure type, but anecdotally, platforms are typically erected in open salt

marshes, telephone poles are typically in utility right-of-ways, cell towers and light poles are

usually in urban landscapes. Structures are therefore in a diversity of landscapes and still equally

successful at producing young.

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Landscape Context

Nest sites were located in landscapes dominated by Urban, Deciduous and Herbaceous

Wetlands, and Coastal Waters. The landscape context of nesting sites changed over time. As the

population increased, more nest sites were located in urban landscapes in greater proportion than

the entire landscape (Table 3). The RI osprey population appears to not only do well in human

dominated landscapes, but also seek nest locations within urban landscapes. Other studies have

found that ospreys are not as successful within human influenced landscapes (Swenson 1979,

Van Daele & Van Daele 1982). Bai et al. (2009) found that an osprey population in Germany

shifted their use of land cover from forested areas to agricultural. The RI population did shift

away from forested landscapes but to urban landscapes (Table 2). The RI population probably

did not make the shift to agriculture, because agriculture comprises a small percentage of the

total landscape (5.3%). However, Bai et al. suggested that the shift they observed was due to the

eutrophication of water bodies surrounding agriculture landscapes, which increase water body

productivity. Urban landscapes can have a similar effect through nutrient runoff, a possible

explanation of ospreys nesting in the RI urban landscape. Another explanation is the pattern of

human development intersects osprey site selection patterns. Ospreys in Rhode Island nest along

coastal areas, and humans tend to settle intensely along coastal regions. The observed pattern

could be a byproduct of human development trends.

The distance between nest sites also changed over time. There was a decrease in the

average distance between active nest sites. The decrease was not linear though. Overall, there

was an approximate decline of 5000 meters between nest sites. The decline occurred gradually in

some years and then sharply in others. There were three sharp declines, the first was between

1977 and 1981, then again between 1989 and 1992, and the last appears recently between 2007

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and 2012. The sharp declines appear to correspond with an increase in active nest sites. It

appears that as the population increases, ospreys are nesting near conspecifics when possible and

then expanding their range into new territory. Hence, the increases in nesting distance after the

sharp declines in distance. Ospreys gain protection from predators by nesting in colonies (Hagan

and Walters 1990) but there may be other benefits and costs of colonial nesting. Bretagnolle et

al. (2008) found a similar pattern in nest distance among colonizing ospreys in a western

Mediterranean population. They found periods of decline, followed by periods of stability where

provisioning rate and prey size increased as the density of ospreys increased, however

productivity decreased. The RI population exhibited the same pattern of decline in reproductive

success while the distance between nest sites decreased. The reproductive rate declined from 1.8

to 1.0 between 1988 and 1993, encompassing the same period when nesting distance declined

sharply, e.g. increase in nest density (Figure 4). One area of future research is analyzing clusters

of nest sites and how they change over time and how reproductive metrics are influenced.

Conclusion

The RI osprey population is increasing and there is no indication at this time that the

population is stabilizing. The growth is occurring with the support of artificial platforms. Based

on the pattern of colonization and reproductive rate, platform location should be within 2 km of

other nest sites, but an effort to locate platforms in areas without existing nest structures should

be made. This would ease the density dependent effects observed in osprey populations. In

addition, based on observed patterns, nest sites should be located in areas with deciduous and

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herbaceous wetlands within 3 km, and urban landscapes do not appear to negatively affect

ospreys, so selecting locations within an urban landscape may benefit ospreys in RI.

Future research should focus on understanding the dynamics between fish stocks and

yearly production. In addition, contaminant exposure can affect population growth, so an

assessment of potential contaminates that are affecting the RI population is recommended.

Because the Rhode Island population bottlenecked and is repopulating near urban land cover, an

in-depth review of the effects of landscape on site selection, population distribution, nesting

behavior, and success should be a focus of future research.

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21

Appendix A

Figure 1. The total recorded number of Active and Successful osprey nest sites in Rhode Island between 1977 and 2012.

Figure 2. The total number of observed osprey fledglings in Rhode Island between 1977 and 2012.

0

20

40

60

80

100

120

140

# of

Nes

ts

Total Number of Active and Sucessful Nest Sites

Active

Successful

0

20

40

60

80

100

120

140

160

180

200

1977 1979 1981 1983 1985 1987 1989 1991 1993 1995 1997 1999 2001 2003 2005 2007 2010 2012

Nu

mb

er o

f F

led

glin

gs

Total Number of Osprey Fledglings

22

Figure 3. The average number of osprey fledglings per successful nest in Rhode Island between 1977 and 2012.

Figure 4. The average number of osprey fledglings per Active nest, also known as the reproductive rate with the replacement rate of 0.08 (Blue Line).

0.0

0.5

1.0

1.5

2.0

2.5

3.019

7719

7819

7919

8019

8119

8219

8319

8419

8519

8619

8719

8819

8919

9019

9119

9219

9319

9419

9519

9619

9719

9819

9920

0020

0120

0220

0320

0420

0520

0620

0720

0820

1020

1120

12

Nu

mb

er o

f F

led

glin

gsAverage Number of Fledglings per Successful

Nest Site

0.0

0.5

1.0

1.5

2.0

1977

1978

1979

1980

1981

1982

1983

1984

1985

1986

1987

1988

1989

1990

1991

1992

1993

1994

1995

1996

1997

1998

1999

2000

2001

2002

2003

2004

2005

2006

2007

2008

2010

2011

2012

Nu

mb

er o

f F

led

glin

gs

Average Number of Fledgelings per Active Nest

23

Figure 5. The number of Active osprey nests in Rhode Island per year per structure type between 1977 and 2012.

Figure 6. The average number of osprey fledglings per structure type in Rhode Island between 1977 and 2012.

0

10

20

30

40

50

60

Nu

mb

er o

f A

tive

Nes

tsNumber of Active Nests per Year

cell

light

platform

telephone

tree

0.00

0.50

1.00

1.50

2.00

2.50

cell channel light other platform telephone tree unknown

Nu

mb

er o

f F

led

glin

gs

Average Number of Fledglings per Structure Type

24

Figure 7. The average percent Successful osprey nest site per structure type in Rhode Island between 1977 and 2012.

Figure 8. The percent Successful osprey nest sites of the Active Cell tower structured nest sites in Rhode Island between 1977 and 2012.

0

0.2

0.4

0.6

0.8

1

1.2

1.4

cell light other platform telephone tree unknown

Per

cen

t

Average Percent Successful Nests per Structure Type

0

0.2

0.4

0.6

0.8

1

1.2

Percent Successful Cell Tower Nest Sites of the Active Sites

25

Figure 9. The percent Successful osprey nest sites of the Active Platform structured nest sites in Rhode Island between 1977 and 2012.

Figure 10. The percent Successful osprey nest sites of the Active Telephone structured nest sites in Rhode Island between 1977 and 2012.

0

0.2

0.4

0.6

0.8

1

1.219

7719

7819

7919

8019

8119

8219

8319

8419

8519

8619

8719

8819

8919

9019

9119

9219

9319

9419

9519

9619

9719

9819

9920

0020

0120

0220

0320

0420

0520

0620

0720

0820

1020

1120

12

Per

cen

tPercent Successful Platform Nest Sites of the

Active Sites

0

0.2

0.4

0.6

0.8

1

1.2

1977

1978

1979

1980

1981

1982

1983

1984

1985

1986

1987

1988

1989

1990

1991

1992

1993

1994

1995

1996

1997

1998

1999

2000

2001

2002

2003

2004

2005

2006

2007

2008

2010

2011

2012

Per

cen

t

Percent Successful Telephone Nest Sites of the Active Sites

26

Figure 11. The average distance between osprey nest sites in Rhode Island between 1977 and 2012.

Figure 12. The overall distribution of land cover types in Rhode Island in 1972, 1985, 1999, and 2010.

0

1000

2000

3000

4000

5000

6000

7000

8000D

ista

nce

(m

)Average Distance Between Nest Sites

0.0%

10.0%

20.0%

30.0%

40.0%

50.0%

60.0%

Distribution of Land Cover within Rhode Island

1972

1985

1999

2010

27

Figure 13. The distribution of land cover types within 3km of osprey nest sites in Rhode Island in 1972, 1985, 1999, and 2010.

Figure 14. The percent change of osprey fledglings in Rhode Island from the previous year's total production between 1977 and 2012.

0.0%5.0%

10.0%15.0%20.0%25.0%30.0%35.0%40.0%45.0%50.0%

Distribution of Land Cover within 3 km of Osprey Nest Sites

1972

1985

1999

2010

-40.0

-20.0

0.0

20.0

40.0

60.0

80.0

100.0

120.0

140.0

1977

1978

1979

1980

1981

1982

1983

1984

1985

1986

1987

1988

1989

1990

1991

1992

1993

1994

1995

1996

1997

1998

1999

2000

2001

2002

2003

2004

2005

2006

2007

2008

2010

2011

2012

Percent Change of Fledglings from Previous Year

28

Figure 15. The total number of Active osprey nest sites in Rhode Island per structure type between 1977 and 2012.

Figure 16. The total number of Successful osprey nest sites in Rhode Island per structure type between 1977 and 2012.

2 11

103141

206

308360

664

0

100

200

300

400

500

600

700

channel other tree cell light unknown telephone platform

Nu

mb

er o

f A

ctiv

e N

est

Sit

esTotal Number of Active Nest Sites per

Structure Type

0 9

78116

170218

279

520

0

100

200

300

400

500

600

channel other tree cell light unknown telephone platform

Nu

mb

er o

f S

ucc

essf

ul N

est

Sit

es

Total Number of Successful Nest Sites per Structure Type

29

Figure 17. The distribution of all nest sites in Rhode Island as of 2012.

30

Figure 18. The percent of land cover within 3 km of osprey nest sites in RI adjusted for the amount of coastal water.

Imagery/Model Year Cohort of Years Number of Years Number of Nests

1972 1977-1981 4 19

1985 1982-1992 11 56

1999 1993-2003 11 119

2010 2004-2010 6 205

Table 1. The imagery years used in the land cover analyses and the associated nesting years.

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

Per

cen

t A

rea

Percent Area of Land Cover within 3km of Nest Sites Fixed for Open Coastal Water

1972

1985

1999

2010

31

RI Land Cover Change

Buffer Land Cover Change Difference

Agriculture 5.2% 5.9% 0.8% Coniferous Forest 2.8% 3.1% 0.2% Coniferous Wetland -0.3% -0.7% -0.5% Deciduous Forest -27.6% -27.6% 0.0% Deciduous Wetland 1.0% -4.8% -5.8% Herbaceous Wetland -1.3% -2.6% -1.3% Mixed Forest 9.9% 6.5% -3.4% Urban 8.5% 18.7% 10.2% Open Water 0.0% -1.5% -1.5%

Table 2. The percent change of each of the 12 categories of land cover for the entire state of Rhode Island and the 3 km buffer zones surrounding each nest site between 2010 and 1972. The far right column indicates the difference between the overall change within the buffers and the total landscape. For example, there was an increase in Agriculture between 1972 and 2010 by 5.2% and within the buffer zone by 5.9%. Therefore, Agriculture increased within the buffer zone over the entire landscape by 0.8%. The areas highlighted in yellow are considered significant increases or decreases in land cover use compared to the entire landscape.

1972  1985 1999 2010

Average Difference over Time 

Agriculture  0.0%  1.3% 0.8% 0.7% 0.7% Coniferous Forest  ‐1.2%  ‐2.3% ‐0.9% ‐1.0% ‐1.3% Coniferous Wetland  0.4%  0.2% 0.0% ‐0.1% 0.1% Deciduous Forest  ‐5.7%  ‐6.1% ‐8.4% ‐5.7% ‐6.5% Deciduous Wetland  6.1%  4.0% 1.0% 0.2% 2.8% Herbaceous Wetland  2.3%  1.6% 1.1% 0.9% 1.5% Mixed Forest  ‐0.3%  ‐2.4% ‐1.5% ‐3.7% ‐2.0% Urban   ‐3.4%  2.4% 6.7% 6.8% 3.1% Open Water  1.5%  0.9% 0.5% 0.1% 0.8% 

Table 3. The percent difference between the 3 km osprey nest buffer zone and the entire Rhode Island landscape for of each of the 12 categories of land cover for each year. The far right column indicates the average difference between the overall change within the buffers and the total landscape. For example, on average the landscape within 3 km of an osprey nest site had 6.5% less Deciduous Forest than would be expected given the total coverage of Deciduous Forest for the state. The highlighted values are considered significant because they are greater than 1%.