National Park Service

U.S. Department of the Interior

Natural Resource Stewardship and Science

The Potential Impact of Sea Level Rise on Seabird 

Nesting Islands in Acadia National Park

Natural Resource Report NPS/ACAD/NRR—2015/1055
ON THE COVER

Northeastern spit on Great Spoon, from the island peak. Note seawall and partially flooded marshy area in foreground.

Photograph courtesy of the National Park Service 
The Potential Impact of Sea Level Rise on Seabird 

Nesting Islands in Acadia National Park

Natural Resource Report NPS/ACAD/NRR—2015/1055

John Anderson

College of the Atlantic

105 Eden Street 

Bar Harbor, ME 04609

October 2015

U.S. Department of the Interior

National Park Service

Natural Resource Stewardship and Science 

Fort Collins, Colorado
ii

The National Park Service, Natural Resource Stewardship and Science office in Fort Collins, 

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Please cite this publication as:

Anderson, J. 2015. The potential impact of sea level rise on seabird nesting islands in Acadia 

National Park. Natural Resource Report NPS/ACAD/NRR—2015/1055. National Park Service, Fort 

Collins, Colorado.

NPS 123/130051, October 2015
iii

Contents 

Page

Figures...................................................................................................................................................iv

Tables.....................................................................................................................................................v

Executive Summary.............................................................................................................................vii

Acknowledgements...............................................................................................................................ix

Introduction............................................................................................................................................1

Bird Islands and the Problem of Sea Level Rise ............................................................................2

Assumptions in our Work...............................................................................................................3

Methods..................................................................................................................................................5

Results..................................................................................................................................................11

The Islands....................................................................................................................................12

Millikan ...................................................................................................................................12

Thrumcap.................................................................................................................................14

Schoodic ..................................................................................................................................17

Little Duck...............................................................................................................................21

Green, Drum, and Scrag Islands..............................................................................................22

Heron Island ............................................................................................................................24

Great Spoon Island ..................................................................................................................26

Little Spoon .............................................................................................................................30

White Horse and Black Horse .................................................................................................32

Shabby Island ..........................................................................................................................33

Conclusions..........................................................................................................................................37

Literature Cited ....................................................................................................................................39
iv

Figures 

Page

Figure 1. Typical Guillemot nesting habitat, Great Duck Island. .........................................................4

Figure 2. Study area showing existing ANP holdings and easements and study islands 

selected for the project. ..........................................................................................................................5

Figure 3. Determining elevations using total station. Great Spoon Island............................................7

Figure 4. Nesting ledge off Milliken Island Blue Hill Bay.................................................................13

Figure 5. Milliken Island nesting ledge. Note shoreline/seaweed wrack along crest of 

island....................................................................................................................................................13

Figure 6. a) Cormorant nests, Thrumcap. Island, b) Cormorant nest (detail). ....................................14

Figure 7. Thrumcap Island from the West. Note height of breaking wave.........................................15

Figure 8. Eastern side of Thrumcap Island showing current shoreline and partial 

elevation...............................................................................................................................................15

Figure 9. Flooding model of Thrumcap Island generated using ARCMAP10.2. The white 

area is guano from nesting seabirds. ....................................................................................................16

Figure 10. Nesting Common Eider on Schoodic Island......................................................................17

Figure 11. Cormorant colony on Schoodic Island, aerial photograph June 20 2007. .........................18

Figure 12. Dense vegetation and ideal eider habitat in center of Schoodic Island. ............................18

Figure 13. a) Central section of Schoodic Island. Note cobble berm facing each side. 

Portions of the interior behind the seawall are near or at current sea level, and brackish 

pools form in areas of poor drainage, b) Western berm or seawall protecting center of 

Schoodic Island, c) Low-lying marshy “core” of Schoodic Island looking north to higher 

rocky outcropping. ...............................................................................................................................19

Figure 14. Flood simulations for Schoodic Island. Note that this is actually an optimistic 

assessment as it assumes no erosion of the mid-island cobble berms..................................................20

Figures 15. Little Duck Island shoreline, a) distant and b) close-up...................................................21

Figure 16. Projected impact of sea level rise on Little Duck Island. ..................................................22

Figure 17. a) Green Island, NW shore, b) Scrag Island from NW and c) Drum Island 

from NW. .............................................................................................................................................23

Figure 18. Green Island N. Shore........................................................................................................24

Figure 19. a) N. shore Heron Island, b) sea-wall, Heron Island, c) sea-wall on Heron 

Island (note flooded area behind the wall), d) glacial erratics within central area of Heron 

Island, and e) detail of glacial erratic, Heron Island. ...........................................................................25

Figure 20. Flood models for Heron Island..........................................................................................26
v

Figures (continued)

Page

Figure 21. a) Great Spoon from north, showing highest elevation and a portion of the 

cobble berm (left), and b) cobble berm on northern side of Great Spoon (note adult Bald 

Eagle perched immediately to the right of the driftwood pile). ...........................................................27

Figure 22. a) Northeastern spit on Great Spoon, from the island peak (note seawall and 

partially flooded marshy area in foreground), and b) south face of Great Spoon sea-wall 

(note storm-line half way down)..........................................................................................................28

Figure 23. Flood models for Great Spoon Island. Note that the northern “handle” is 

currently connected to the main island only at low tide. .....................................................................29

Figure 24. a) Northwestern end of Little Spoon Island (note high sides, basalt/granite 

composition, and tapering of island’s extremities), and b) close-up of northeastern 

shoreline of Little Spoon Island...........................................................................................................30

Figure 25. Flood models for Little Spoon Island. ...............................................................................31

Figure 26. a) White Horse Island, and b) Black Horse Island. ...........................................................32

Figure 27. Flood models of Black Horse Island. ................................................................................33

Figure 28. a) Shabby Island from the East, and b) Shabby Island close-up of shoreline....................34

Figure 29. Flood models of Shabby Island. Ledges to northwest are already largely 

submerged at extreme high tide. ..........................................................................................................35

Tables 

Page

Table 1. Estimates of nesting seabirds on study islands......................................................................12

vii

Executive Summary

A multi-year study of seabird nesting islands owned in fee or under conservation easement to Acadia 

National Park, Maine was conducted between 2011 and 2014. A total of 13 islands (3 under feeownership, 10 with easements) were identified for detailed study. Islands were censused through a 

combination of boat-counts and direct colony walk-throughs, with detailed nest counts performed for 

Herring and Great Black-backed gulls and Double-crested cormorants. Presence of nesting Eider 

ducks and Black guillemots was also noted.

Detailed photographs of island shorelines and key habitats were taken for each island, and a 

“biological shoreline” marking the lower limit of the area above which wave action was unlikely 

during the breeding season (May-August) was developed using sub-meter accurate differential GPS 

and a total-station transit. Island topography was obtained from LIDAR files available from the State 

of Maine Office of GIS. These files were combined with the GPS/transit data from individual islands 

and were used to generate probable flood maps under different scenarios ranging from a 1 to a 3m 

increase in sea level. Islands were classified on the basis of perceived vulnerability ranging from 

'unlikely to persist as viable colony site’ (Category 1) through ‘subject to some habitat loss’ 

(Category 2) to ‘minimal loss of effective habitat’ (Category 3). Four islands (Milliken, Drum, White 

Horse and Black Horse) fell into Category 1, mainly because of their small size. Six islands 

(Schoodic, Heron, Shabby, Great Spoon, Green, and Shag) fell into Category 2; in the case of the 

larger islands, due to the likelihood of the failure of cobble sea-walls, leading to habitat loss or 

fragmentation. Three islands (Little Duck, Thrumcap, and Little Spoon) fell into Category 3, with 

some habitat loss but insufficient to seriously compromise nesting populations.

We observed evidence of significant declines in nesting seabirds throughout the study area when 

compared to past studies. Much of this decline is probably due to predation and disturbance by Bald 

Eagles, and possibly in some cases additional disturbance from human intruders. Bald Eagles were 

present on or around all islands in the study area, and were frequently seen flying over or landing in 

gull colonies. We found evidence of predation on several islands, including the remains of both 

adults and birds of the year.

Although no direct NPS mitigation strategies for sea level rise are currently feasible, we encourage 

the National Park Service to:

• Continue to educate the public about the Park’s islands, seabirds, climate change and sea 

level rise. This could include additional curricula for High School or K-8 students, 

informational posters and brochures, and Ranger talks at major campgrounds and the Visitor 

Center. 

• Develop adequate signage cautioning visitors to stay off nesting islands during the breeding 

season (May-Aug).

• Examine possible acquisition of additional nesting islands in partnership with other Federal, 

State or private conservation groups.
viii

• Establish a regular monitoring program (at least every 3 years) of Park-owned or easement 

nesting islands. Ideally this program will include both regular nest counts and geo-referenced 

photographs depicting island shoreline conditions.

• Designate an individual to be responsible for regular update of island information, which 

should be maintained as a GIS or other searchable database.

• Consider possible acquisition of additional nesting islands if this is within the NPS mandate 

and fee area.

Acadia National Park is responsible for several key nesting sites in Mid-coastal Maine. It is to be 

hoped that in spite of recent declines in nesting bird numbers and the long-term challenge of sea level 

rise and other aspects of climate change, these islands will continue to play an integral role in the 

park’s mission and heritage.
ix

Acknowledgements

I would like to thank Mary Foley, Regional Chief Scientist, National Park Service, for arranging the 

support of this project from inception to conclusion. Mary had both the courage and the inspiration to 

take a casual comment by the author as the catalyst for serious study, she then found the resources to 

make it happen. I would also like to thank Karen Anderson, Geographer, Acadia National Park for 

assistance with the mysteries of ArcMap, LIDAR, and spatial geodesy, Jane Strader, who collated 

data, generated the flood model maps, and wrote the accompanying High School curriculum on sea 

level rise. Field work would not have been possible without Kate Shlepr, team leader for the Great 

Duck field crew, the crew itself from 2011-2013, and Capt. Toby Stephenson and the crew of the RV 

Osprey, who took us out and got us back. Write-up of this work benefitted extensively from the 

comments of two anonymous reviewers. Funding for this study came from the Northeast Region of 

the National Park Service and the Drury Research Fund of the College of the Atlantic.

1

Introduction

For more than a century the Gulf of Maine –the region of coastline and ocean that includes Acadia 

National Park (ANP)- has provided nesting and feeding sites for a broad range of seabirdsi including 

gulls, ducks, guillemots, terns and petrels. Estimates have suggested that perhaps as much as 50% of 

all breeding seabirds in the eastern United States are found on Maine islands, and the region contains 

a number of Important Bird Areas (IBA).ii

Islands also serve as significant stop-over points for 

migratory species in fall and spring.

Seabirds, including members of the Procellariformes (petrels and their allies) and Charadriiformes 

(gulls, terns and allies) are primarily ground or burrow nesters, and are therefore particularly 

vulnerable to mammalian predators such as mink, fox or coyotes. They are also susceptible to 

disturbance by humans, and their tendency to nest in large colonies at relatively few sites can result 

in serious population-level disruptions with even a few disturbances or active predators. Cormorants, 

such as the Double-crested cormorant (Phalacrocorax auritus) are known to nest in trees, but their 

nitrogen-rich wastes rapidly kill off nesting trees, and the birds are then forced to nest on the ground, 

where they become immediately vulnerable to terrestrial mammals.

Because of this sensitivity to terrestrial threats, seabirds nest almost exclusively on islands, and their 

colonies are often located on relatively remote and/or inaccessible sites. Many of these islands are in 

highly exposed off-shore locations, and as such are vulnerable to over-topping or erosion by storm 

waves to an extent not found in more protected in-shore areas. Extended periods of incubation, 

coupled with a high level of pre-fledging care, place adult birds and their young at risk from weather 

extremes including storm-surge, tidal events, and intense rainfall, all of which can occur during the 

April-October breeding and immediate post-fledging period.

The shoreline and islands of Maine represent an extremely dynamic landscape,iii

within which 

present configurations are less than 5000 years old. The entire area was heavily glaciated up until 

approx. 15000 years B.P. after which complex interactions between isostatic re-bound and increases 

in post-glacial water volumes resulted in a series of flooding and recession events. For much of the 

period 9000 B.P. to approx. 5000 B.P., present day islands would have been alternately connected to 

the mainland or under water, and in either case unsuitable as sites for nesting seabirds. 

Archaeological evidence of Native American use of seabirds other than the Great Auk (Pinguinus 

impennis) is scarce (Spiess and Lewis 2001) iv

, while remains of the (now extinct) Sea Mink 

(Neovison macrodon) in island shell middens are common. The implication is that seabird numbers 

in pre-Colonial times were probably much lower than that recorded in the early 20th century, however 

we lack any systematic surveys prior to the late 1890’s. Present conditions must be regarded as 

somewhat transitory, however the historical record v makes it clear that islands in eastern Maine in 

the vicinity of Acadia National Park have included significant seabird nesting sites since at least the 

last quarter of the 19th century.

Acadia National Park (ANP) is centered on extensive holdings of over 12,300 ha on Mt Desert 

Island, Hancock Co. Maine, with significant additional components on Isle au Haut (1092 ha) and the 

extreme southern end of the Schoodic Peninsula (957 ha). These three units contain many valuable 
2

biological, recreational, and cultural features, and provide recreation opportunities for over 2.5 

million visitors per year; however none is of particular significance to nesting seabirds. ANP 

manages more than 100 outlying islands as components of the park. These islands, while small in 

total area, include several important seabird colonies.

Bird Islands and the Problem of Sea Level Rise

Sea level rise is of increasing concern to resource managers, land owners, and ecologists involved in 

coastal environments. A recent report vi

has suggested four possible scenarios for expected sea level 

rise along the coastal United States, ranging from a low of 0.2m (0.7 ft.) to a high of 2.0m (6.6 ft.) by 

the year 2100, using mean sea level height in 1992 as an arbitrary “zero point”. Understandably, 

much of the focus to date has been on effects on human infrastructure, property-protection and 

safety, but sea level rise is also of great concern in the conservation of species such as ground-nesting 

seabirds that rely on small islands as safe refuges from terrestrial predators. The Gulf of Maine is an 

important region for seabird conservation. Islands within the Gulf serve as nesting and loafing areas 

for a variety of species, including Leach’s Storm Petrels (Oceanodroma leucorhoa), Black 

Guillemots (Cepphus grylle), Common Eiders (Somateria mollissima), Herring and Greater Blackbacked Gulls (Larus argentatus, L. marinus), Double crested Cormorants (Phalacrocorax auritus),

several species of terns (Sterna sp.), Razorbill Auks (Alca torda) and Atlantic Puffins (Fratercula 

arctica). In addition, islands support unique floras, containing rare or endangered species of plants, 

some of which represent residual stands of species present in the area since the end of the Pleistocene 

glaciation. Many ledges serve as important “pupping zones” or haul-outs for Gray and Harbor Seals 

(Halicoerus grypus and Phoca vitulina).

ANP has easements on, or fee ownership of, over 100 islands between Penobscot Bay (43o49’ N, 

69o05’W) to Schoodic Point (44o 20’N 68 01’ W). Although many of these islands are unsuitable for 

nesting areas at this time due to human activities or the presence of predatory mammals, some are 

known to contain –or have histories of containing- significant populations of breeding birds. Unlike 

the sandy “barrier islands” common to the south, Maine islands are generally granitic or basaltic 

ledges, often surrounded by a cobble “berm” that is constantly re-arranged by the high energy storm 

surges of late summer and winter. Even minor changes in sea level could have a profound impact on 

island size or configuration, reducing the area available for nesting or increasing the likelihood of 

eggs or chicks being washed away during storm events. Of longer term concern is that some islands 

will simply disappear as water levels rise; granite and cobble islands lack the ability to move and 

reform as exhibited by many barrier islands. 

As a result of these concerns the National Park Service contracted with College of the Atlantic to 

conduct a multi-year assessment of Park islands in the Acadia N.P. to assess the probable effects of 

changes in sea level on nesting seabirds. Additional goals were to get a better sense of the presence 

of nesting birds within the Park as a whole, and also to record additional ecological and/or natural 

history information for use in park management decisions. The project was designed as a three year 

effort in the field, involving collaboration with NPS and CESU partners and including an educational 

component on the general effects of sea-level rise and climate change on ANP suitable for teaching 

to High School students.
3

Assumptions in our Work

For the purposes of this study we focus on a reasonable probability of a 1m rise in mean sea level by 

2100 as a “most likely” scenario, though we included examples of greater increases for comparative 

purposes. This is midway between the low and high models in the report cited above, and is also 

slightly below the midpoint of estimates published by the National Academies of Science.vii Both 

estimates assume no major loss of the Greenland or Antarctic ice Shelves –events that would make 

any conclusions in this report largely irrelevant. 

In assessing the impact of sea level rise on nesting seabird populations it is important to consider a 

number of factors and aspects of particular species’ natural history. Simple linear measures of sea 

level rise, while important in some cases, need to be weighed in relation to their likely effect on long 

term storm damage and erosion. Because the primary charge of this project was to examine impacts 

on nesting birds, the importance of data on tide height, storm surges, etc. are strongly, though not 

exclusively, of seasonal import. A major storm likely to occur in September or October may have 

very little impact on nesting success (although it could create or destroy habitat useful in subsequent 

breeding seasons), whereas the same storm in mid-July could be devastating. Obvious winter storm 

lines could be found on several of the islands that we studied, but on rocky shores not prone to 

erosion, they are probably of minimal importance compared to possible surges in May-July. Maine is 

fortunate in that, although it sits in the storm track of Atlantic hurricanes, the majority of these storms 

have historically arrived from late August until the end of October.viii

While there is some discussion 

about possible increased frequency of major storms ix, at least at present, this pattern seems to be 

holding true.

One must recognize that different species require different habitat substrates, which may themselves 

be a product of existing shorelines or may be affected by wave action to a greater or lesser extent.

These substrates in turn may limit the proportion of an island that may be suitable for nesting. We 

assume that the surfaces of many shorelines are the direct result of long-term wave processes, and 

that vegetation structure is in turn affected by both substrate and frequency of wash-over and spray. 

Storm activity may eliminate habitat on one area of a large island while simultaneously creating new 

habitat in another. For example Black Guillemots require rocky clefts or crevices for nesting sites –

habitat that is produced along particular shores by the action of winter waves moving large granite 

boulders (Fig. 1). Smaller rounded cobbles tend to fit together too tightly to provide adequate nesting 

crevices, while overly large slabs may provide access to predators. Observations over the past 16 

years on Great Duck Island have shown that, whereas guillemots tend to frequent the same general 

areas of shoreline from one year to the next, they may abandon a particular crevice as it is closed 

between one storm season and the next, and make use of a new neighboring site that has opened up 

as a result of wave “engineering”. Once one recognizes the relationship between exposure, rock slab 

formation and positioning, and guillemot nesting behavior, even a superficial survey of a given 

shoreline can provide the observer with a high probability of correctly identifying where guillemots 

are not likely to be found. Further assessment is required to confirm actual nesting. Guillemots can 

nest within 3m of the upper tide line, and as such, are the first to be exposed to changes in overall sea 

level.
4

Figure 1. Typical Guillemot nesting habitat, Great Duck Island.

The unconsolidated nature of guillemot habitat and its proximity to the shoreline, places this sort of 

habitat (and species’ dependence on it) at greatest risk to increases in sea level or storm-surge 

frequency compared to species utilizing more upland or consolidated areas. By contrast, gulls 

typically partition small islands, with Great Black-backs occupying the highest (least vulnerable) 

areas and Herring Gulls forming a band between them and the guillemots.
5

Methods 

The bulk of the project during the late winter and spring of 2011 was devoted to assembling a 

Geographic Information System (GIS) containing Park ownership and easement data for islands and 

tying this to existing data on nesting islands. The primary source of nesting information was Erwin 

and Korschgen (1979) x supplemented with more recent information from the U.S. Fish and Wildlife 

Service (Anonymous 2010) xi

and the author’s personal observations. Data for park boundaries, 

easements, and fee ownership were obtained from the ANP Resource Management Division, who 

also provided preliminary LIDAR data for the islands.

As a result of the initial examination of GIS and seabird data, a total of 13 islands were selected for 

further inspection (Fig. 2).

Figure 2. Study area showing existing ANP holdings and easements and study islands selected for the 

project.
6

Selected study islands consisted of:

1) Thrumcap Island, lower Frenchman Bay, Coastal Registry # 59-300 owned in fee by the 

National Park Service.

2) Schoodic Island, southwest of Frenchman Bay, Coastal Registry # 59-062 owned in fee by the 

National Park Service

3) Little Duck Island, south of Mount Desert Island, Coastal Registry # 59-439 privately owned, 

NPS easement.

4) Heron Island, south of Swan’s Island, Coastal Registry # 59-480 owned in fee by the NPS.

5) Great Spoon Island east of Isle au Haut, Coastal Registry # 63-287 an easement island.

6) Little Spoon Island east of Isle au Haut Coastal Registry # 63-289 an easement island.

7) Shabby Island, Jericho Bay Coastal Registry # 59-996, an easement island. 

8) Green Island south of Blue Hill Bay Black Island , Coastal Registry # 59-446, an easement 

island

9) Scrag Island south of Blue Hill Bay Black Island, Coastal Registry # 59-445 an easement island

10) Drum Island south of Blue Hill Bay Black Island, Coastal Registry # 59-444 an easement 

island

11) White Horse south of Isle au Haut Coastal Registry # 63-293 an easement island

12) Black Horse south of Isle au Haut Coastal Registry # 63-294 an easement island

13) Indian Point Ledge/Milliken Island Blue Hill Bay Island Coastal Registry # 59-127 an 

easement island

All of these islands have been reported xii to have numbers of nesting seabirds within the past 15 

years. 

Additional information on specific aspects of nest site selection and phenology was collected on 

Great Duck Island, south of the Cranberry Islands (Coastal Registry # 59-440), focusing on precise 

locations of nesting seabirds in relation to the existing shoreline. Great Duck was selected for these 

data as the island is the site of College of the Atlantic’s Eno Field Station, and gulls, guillemots and 

petrels are already under study at and around the station. We could thus get spatial information with 

minimal additional disturbance to nesting birds. Ultimately it would seem advisable to obtain 

comparable information from at least some of the other study islands, however this would require 

longer stays and greater levels of disturbance than the present study permitted.

Elevations for most islands were obtained from LIDAR data and in some cases a total station transit 

(Fig. 3).
7

Figure 3. Determining elevations using total station. Great Spoon Island.

The exact location of the relevant “high tide line” in relation to seabird nesting is, as mentioned 

above, difficult to determine. For purposes of this study we elected to use an elevation determined 

from a minimum of 4 points exhibiting either sessile marine invertebrates or attached algae to 

represent the most likely region of frequent wetting. After our initial season (2011) we mapped this 

“biological shoreline” using Trimble Geo XT 2005 series GPS units differentially corrected through 

post-processing using the CORS-BAR HARBOR reference station for correction. Corrected GPS 

data provided sub-meter horizontal accuracy for greater than 90% of all positions in most cases.

While our selection of biological cues for current shoreline is an approximate assessment of basal 

height, it is probably within acceptable margins of error for the purposes of this study. We tested our 

assignment of the shoreline on both Schoodic and Thrumcap islands by having different researchers, 

each equipped with an identical GPS unit walk the shoreline in opposite directions and then overlaid 

the resulting polygons on each other. The results were within the expected margin of error for the 

equipment, and suggest that there is a high degree of repeatability in this sort of estimate at least for 

some islands.

LIDAR and survey data were incorporated into a common GIS using ARCMAP 10.2 (ESRI 2014) 

and flooding models were generated for 8 of the 13 islands using the ARCMAP software and 

estimates of best (no significant rise), optimistic (0-1m rise) pessimistic (1-2m rise) and catastrophic 

(2-3m rise) scenarios were generated. In addition to our own surveying work, we assisted ANP 
8

personnel in establishing fixed benchmarks on Thrumcap, Schoodic, Heron and Little Duck islands 

for future monitoring. These monuments were then surveyed using survey grade GPS units with subcentimeter accuracy. The points are the backbone of a park-wide height monitoring network.

Accurate estimates of nesting seabird populations are often difficult to obtain as they may be heavily 

influenced by seasonality, methodology, and even time of day in the case of species such as 

guillemots. In making comparisons with past estimates we attempted to duplicate methodologies 

used in prior counts that had the highest repeatability. Particular attention was paid to a 

comprehensive survey conducted in 1995, as we felt that the time range involved might be 

particularly revealing in terms of trends. Not all islands had been surveyed in the same year, and 

when data for 1995 were absent, we selected the closest available date from information in Allen et 

al. (2012).

In our own work, island populations of nesting seabirds were determined whenever possible by 

ground counts of active nests. These counts consisted of a line of 3-7 people walking at arms-length 

in repeated swaths across an island, recording clutch size and total numbers of nests in the case of 

gulls, Eider ducks, and cormorants and presence/absence in the case of guillemots and petrels. In 

2012 we used plastic rings, supplied by the USFWS to discriminate between Herring and Great 

Black-backed Gulls based on egg diameter. Unfortunately, a re-evaluation of this methodology in 

2013, using nests of known provenance (determined by observation of incubating birds on Great 

Duck Island) revealed that this technique may seriously over-estimate the actual number of Great 

Black-backs. As a result, we chose to lump both species into a common category of “gulls” for the 

purposes of this report. Likewise we chose not to discriminate between Great Cormorants 

(Phalacrocorax carbo) and Double-crested Cormorants (P. auritus). Great Cormorants are very rare 

in Maine and their number has declined significantly in the past 20 years. We were not entirely 

confident that all observers could distinguish the two species and so, as with gulls, elected to err on 

the side of caution by lumping both together.

In addition to ground counts, or in situations where time or sea-state prevented landings, we circled a 

given island as closely as possible, observing birds on nests or territories as well as counting 

presumed transients in the inter-tidal. Only Black Horse, White Horse and one of the Green islands 

had only boat counts. Geo-referenced photos were taken of islands during these circumnavigations in 

order to create a reference library of images for later analysis.

In terms of sensitivity to sea level rise, we qualitatively categorized islands as belonging to one of 

three general groups:

1) Small low-lying island and/or exposed to significant storm surge

2) Higher island with points greater than 5m above present sea level, but containing low areas 

subject to flooding or cobble sea-wall likely to erode

3) High rocky island with typical elevations greater than 5m above present sea level.
9

Islands in category 1 are not expected to survive even moderate levels of sea level rise. Islands in 

category 2 will continue to provide at least some habitat for nesting seabirds, although areas currently 

favored by some species may not persist. Islands in category 3 may lose a small proportion of their 

overall shoreline, but will continue to provide significant nesting habitat under currently expected sea 

level rise.

11

Results 

The results of our work indicate that 1) islands differ greatly in terms of probable impact of sea-level 

rise, and 2) factors other than sea-level rise are dramatically altering seabird populations at a much 

more rapid rate than can be expected from current estimates of shoreline change. Islands surveyed 

generally show lower recent seabird numbers than were found roughly two decades ago (Table 1). 

Across three bird groups (gulls, cormorants, and common eiders), recent numbers appear to be lower 

than the past in roughly two-thirds of the estimates (25 of 39 instances). These changes do not seem 

to be due to loss of habitat, as the total decline in usable area between the mid 1990’s and the present 

is relatively minor compared to available nesting space. One island (Thrumcap) has lost all of its 

large trees since the 1980’s. Double crested Cormorants are known to have a preference for treenesting, and some of the continued decline in numbers on that island may be attributable to loss of 

nesting platforms, however substantial numbers of birds continued to nest on the island for more than 

a decade after the last tree fell.

Of potentially greater short-term significance, we were struck by the large number of foraging and 

loafing Bald Eagles (Haliaeetus leucocephalus) that we observed on or around every island that we 

visited. Our high count of 9 individuals on Heron Island in 2012 was followed in 2013 by 5 on the 

same island. Three were seen on Great Spoon, 2 to 5 were regularly seen over Little Duck, and 2 or 

more were seen at or near Thrumcap, Shabby, and the Horses. A figure in Todd and Matula (2008)

xiii shows more than 50 active Bald Eagle nests within the study area, and overall populations of Bald 

Eagles in Maine have been exhibiting near-exponential growth since the mid-1980’s. Bald Eagles are 

known predators on seabirds, and their presence in or over colonies results in immediate disruption 

as adult birds rise to “mob” the approaching predator. We witnessed frequent mobbing events during 

all three years of this study. It is important to note that in many cases eagles were not nesting on 

islands that they were seen foraging over. Nisbet (pers. comm.) has suggested that the presence of a 

nesting pair may reduce attacks by roaming immature eagles at least during the early part of the 

season. While this may be true in some cases, our observations on Great Duck suggest that any relief 

from nesting territoriality may be more than exceeded by subsequent adult and fledgling predation 

later.
12

Table 1. Estimates of nesting seabirds on study islands. In cases where no count had been conducted in 

1995, we selected the closest year to that date when a count had been conducted. It should be noted that 

not all counts used the same methodologies, and these results should be used for general comparisons 

only. Eider counts on larger islands are probably underestimates because eiders begin hatching in late 

May or early June, prior to our counting window. Eider females and chicks leave the nest as soon as 

hatching is completed.

Island Gulls 

1995*:2013

Cormorants 

1995*:2013

Common Eiders 

1995*:2013

Other species present 

2013

Millikan/Indian Point 0:0 0:0 0:0 50 Common Terns in 2000, 

0 in 2013

Thrumcap 141:105 430:12 10:1 Canada Goose

Schoodic 796:479 138:359 1000:23+ 20+ Guillemots 

Little Duck 434:26 378:0 400:20+ 100+ guillemots

Green 37:16 168:0 50:0 Guillemots present

Drum 0:0 0:0 0:0

Scrag 37:24 55:75 20:3 4+ guillemots

Heron 1526:245 0:0 200:10+ 1+ guillemot

Great Spoon 734:65 63:0 494:17+ 3 common terns

Little Spoon 255:157 253:14 100:14 8+ nesting guillemots

White Horse 0:0 4:0

Black Horse 0:0 0:3

Shabby 190:113 312:36 150:8 Guillemots present

The Islands

Millikan

Millikan Island (44 2305.75 N 68 22 46.81 W) is a park easement island located approx. 0.22 km 

from Mt Desert Island. Its greatest significance lies in the long ledge extending to the Southeast (Fig. 

4) that has been used for periodically by nesting Common terns (Sterna hirundo). These birds seem 

to move between the Milliken ledges and other small islands in upper Blue Hill Bay, nesting for a 

year or two on one spot before moving on as their nest site is discovered by predators. It seems 

possible that this strategy of frequent movement by small numbers of birds between multiple ledges 

may represent a long-term historical pattern for some species. No terns or other seabirds were found 

when the island was censused in 2012. The nesting ledges fall into our Category 1 islands, highly 

susceptible to even minor rises in sea level. Virtually all areas used by nesting terns are within 2m of 

the current tide line, and there is little or no upland area that would allow an orderly retreat as waters 

rise (Fig. 5). The island is already subject to periodic flooding/overtopping, and whereas its sheltered 

location in an inlet of the bay reduces the effects of storm surge, it is apparent that much of the island 

floods periodically. Whereas individual terns have been known to nest occasionally on even small 

rocks, it seems likely that once the island ledge is divided into multiple “nubbles” its utility as a 

nesting area will be compromised.
13

Figure 4. Nesting ledge off Milliken Island Blue Hill Bay.

Figure 5. Milliken Island nesting ledge. Note shoreline/seaweed wrack along crest of island.
14

Thrumcap

Thrumcap Island (44 21 08 N, 68 10 36 W), located 0.4 km east of Mt Desert Island, is one of the 

three most significant nesting islands within ANP. Although the population of all species of seabirds 

has been significantly reduced (Table 1) the island still supports limited numbers of Herring and 

Great Black-backed Gulls, Common Eiders, and Double-crested Cormorants. A recent arrival, as of 

2014, was a single pair of Canada geese (Branta canadensis) that appeared to be nesting on the west 

side. The crown of the island was tree-covered until the early 1990’s when the dominant spruce stand 

was killed off by the build-up of nitrogen rich guano from nesting cormorants. Once the dead snags 

had blown over, the cormorants continued to nest on the ground, constructing elaborate nests from a 

mixture of sticks, mud, seaweed, etc. (Fig. 6a-b).

Figure 6. a) Cormorant nests, Thrumcap. Island, b) Cormorant nest (detail).

 

 

a

b
15

Thrumcap Island’s location near the western shore of Frenchman Bay (Fig. 7) makes it the most 

easily observed seabird island in Acadia National Park. In spite of the island’s relatively small area 

(1.3 hectare), its high steep sides (Fig. 8) reduce the likely effects of sea level rise, at least within the 

foreseeable future. As such we regard it as a Category 3 (least sensitive) island.

Figure 7. Thrumcap Island from the West. Note height of breaking wave.

Figure 8. Eastern side of Thrumcap Island showing current shoreline and partial elevation.
16

The cormorant colony has traditionally nested on the extreme peak of the island, while Black-backed 

gulls have gradually pressed Herring gulls into occupying the lower slopes of the island. All three 

species have declined significantly in recent years, while Bald Eagles are increasingly common, both 

passing over and roosting on the island.

GIS modelling of possible flooding scenarios on Thrumcap (Fig. 9) confirm our impression that the 

island is relatively resilient to expected sea level rise.

Figure 9. Flooding model of Thrumcap Island generated using ARCMAP10.2. The white area is guano 

from nesting seabirds.

As shown in Figure 9, the expected 1-meter rise in sea level over the next century has only minimal 

impact on the island’s total area, and even the 2-3 meter sea level rise scenario leaves substantial 

portions of the island above the tide line. It should be noted that we were not in a position to model 

the effects of potential storm surge on erosion, spray, or additional flooding. It must be remembered 

that, at least in reference to historical conditions, peak storm activity occurs after the nesting season 

for the majority of birds utilizing park islands. In addition, Thrumcap consists largely of a rocky 

dome with only minimal soil layers along the summit. Loss of this soil and the vegetation that 

utilizes it would have minimal impact on gulls and cormorants. Eider ducks are generally more 

reliant on vegetation for nesting habitat, but they continue to nest on Mt Desert Rock in the complete 

absence of covering vegetation. Other studies xiv have suggested that while eiders may lose some 

eggs and chicks to gulls, they also benefit from gulls driving off more serious predators, especially 

corvids. Loss of gull populations may therefore be expected to have a negative effect on eiders.

Thrumcap is in close proximity to Bar Harbor and provides excellent opportunities for water-based 

viewing of sensitive wildlife during the summer months. The island is accessible to sea-kayakers, 

although there is only one moderately safe landing place along the present shoreline. As of this 
17

Figure 10. Nesting Common Eider on Schoodic Island. 

writing (July 2015) this landing place has no signage cautioning would-be intruders to avoid the 

island during breeding season (May-August).

Schoodic

Schoodic Island (44 19 51 N, 68 01 57 W), located 0.94 km from Schoodic Peninsula, is without 

question the most important seabird island currently owned in fee by Acadia National Park. The 

island has a long history of seabird nesting, extending back at least into the early 1940’s xv

. The 

island has contained a Bald Eagle nest in spruce trees at the southern end for a number of years. As 

mentioned earlier, it has been 

suggested (I.C.T. Nisbet, pers. comm.) 

that the presence of nesting eagles or 

territorial adults may reduce predation 

on seabirds by roaming juvenile 

eagles. This situation may however be 

changing as eagle populations 

continue to increase. We saw up to 

four immature Bald Eagles at the 

extreme Northeastern end of the 

island, and immature and juvenile 

eagles at the southern end. The island 

supports a large number of nesting 

Common Eiders, particularly in the 

dense vegetation in the center of the 

island (Fig. 10), and both Herring and 

Great Black-backed gulls nest in 

clusters near the shore and along high 

points at the north and south ends of 

the island. There is a large colony of 

Double-crested cormorants on the 

Northeast shore (Fig. 11). In addition, 

we saw large numbers of Black 

Guillemots in the waters immediately 

around the island, and a number 

emerged from rock crevices on the 

island’s periphery as we conducted 

surveying operations. We did not 

attempt any sort of formal census of guillemots, but are confident that they are nesting on the island.

There have been periodic reports of Leach’s Storm Petrels nesting on Schoodic, but a systematic 

survey in 2007 failed to turn up any burrows, and we did not see any during the course of this study.

The island’s dense vegetation may serve as a deterrent to petrels, but it is entirely possible that they 

may attempt to nest in the northern and southern ends in the future.
18

Figure 11. Cormorant colony on Schoodic Island, aerial photograph June 20 2007.

In spite of its relatively large size (26ha), Schoodic

Island’s topography makes it a Class 2 island, likely to 

be impacted by moderate sea level rise through the 

loss of key nesting areas. Most prominent among 

these is the low marshy area in the center of the island 

that is at, or near, present sea-level. This area is 

densely vegetated (Fig. 12) and supports the majority 

of the island’s nesting Common Eider population. 

Even though they may be found nesting under rock 

ledges or even along large-cobble shorelines, Eiders 

prefer tall vegetation for nesting as this provides 

maximal camouflage for nests. Eider females travel to 

and from their nests along tunnels in the vegetation, 

which often branch repeatedly, possibly to further 

confuse would-be predators. At the moment this area 

is protected from wave incursion by high cobble 

seawalls (Fig. 13a-b). Figure 12. Dense vegetation and ideal 

eider habitat in center of Schoodic Island.
19

Figure 13. a) Central section of Schoodic Island. Note cobble berm facing each side. Portions of the interior behind the seawall are near or at 

current sea level, and brackish pools form in areas of poor drainage, b) Western berm or seawall protecting center of Schoodic Island, c) Low-lying 

marshy “core” of Schoodic Island looking north to higher rocky outcropping.
20

Figure 14. Flood simulations for Schoodic Island. Note that 

this is actually an optimistic assessment as it assumes no 

erosion of the mid-island cobble berms. 

Flood modelling (Fig. 14) suggests 

that even moderate increases in sea 

level will reduce the integrity of 

Schoodic Island as a nesting area.

Because the island consists of two 

higher rocky outcroppings connected 

at present by cobble sea walls 

protecting a low-lying marshy core, 

even a slight increase in erosion and 

sea level is likely to split Schoodic 

into two roughly equal fragments. 

Schoodic is heavily exposed to 

weather from the south and 

southeast, and the combination of 

rising sea and increased storm 

frequency (whether or not storms 

come during the breeding season) is 

likely to eventually break the sea 

walls and flood prime eider habitat.

Each of the remaining high segments 

is likely to contain suitable nesting 

habitats for gulls and cormorants, 

and some eiders are likely to 

continue to nest in the more 

vegetated areas of the uplands, but 

all current guillemot nesting habitat 

is likely to be flooded. Salt intrusion 

into the fragmented southern “islet” 

may kill the stand of spruce trees 

currently used for nesting by the 

island’s resident Bald Eagles. At the 

same time, vegetation die-back may 

open up habitat for Storm petrel 

nesting, although data from Great 

Duck suggest that petrels may prefer 

to nest along areas of spruce forest 

edge. Conflicting pressure 

(decreased understory and also loss 

of mature trees) may result in 

relatively little gain for the petrels.
21

Little Duck

Little Duck Island (44 10 23.7 N 68 14 40.5 W) is located 7.44 km South of Mount Desert Island. It 

is a park easement island, currently owned by the National Audubon Society. The island was 

protected starting at the end of the 19th century because of its significant populations of gulls, eiders, 

guillemots xvi and storm petrels. A plaque commemorating the island’s status as a sanctuary may be 

found on the rocks along the Northeast portion of the island’s coastline. A large Double-crested 

cormorant colony occupied spruce trees on the island’s western side during the 1970’s and 1980’s.

The last nesting cormorants were documented in 2011. Little Duck’s relatively high contour (Fig. 

15a-b), size (36ha), and structure as a rounded dome of rock renders it relatively impervious to 

significant impact from sea level rise, making it a Category 3 (least sensitive) island.

Figures 15. Little Duck Island shoreline, a) distant and b) close-up.
22

This level of resilience is supported by our flood models (Fig. 16) which show only limited impact 

on shorelines at even the most pessimistic level of sea level rise.

Figure 16. Projected impact of sea level rise on Little Duck Island.

Flooding effects would be most significant along the island’s south and east shores, but negligible for 

much of the rest of the island. The primary significance of this would be to the island’s Black 

Guillemot population, many of which are known to nest in rocky crevices along the northeastern 

shore. It seems likely however that so long as sea-level rise occurs relatively gradually additional 

habitat would be created in more upland areas. There is plenty of remaining habitat, even under the 

highest sea-level rise scenario, for other species to continue nesting. This is particularly important 

given Little Duck’s status as a major Eider nesting colony. 

Green, Drum, and Scrag Islands

Green (44 09 11.3 N, 68 20 58 W) located 7.5 km SW of Mount Desert Island, Drum (44 09 30.9 N, 

68 19 52.45 W) located 6.96 km SW of Mount Desert Island, and Scrag (44 09 20.6 N, 68 20 26.35 

W) located 7.2 km SW of Mount Desert Island, are sometimes referred to collectively as “the Green 

Ledges”. The Park holds conservation easements on all three islands. Both Green and Scrag Islands 

have been listed as periodic nesting areas for seabirds - particularly gulls, eiders and cormorants - and 

both of these islands contain current nesting habitat for Black Guillemots. We saw guillemots 

emerging from crevices in the rocks during our census activities, but did not attempt a systematic 

survey.
23

All three islands are small, ranging from approx. 2.2 hectares (Green) to less than 0.35 hectares 

(Drum). As shown in Figures 17 a-c the islands are high-sided ledges, with vegetation on the upper 

ridges (Green and Scrag), or essentially naked rock (Drum).

Figure 17. a) Green Island, NW shore, b) Scrag Island from NW and c) Drum Island from NW.

We did not land on Drum Island because of the lack of a suitable landing place and the absence of 

any obvious seabirds. The island was listed in 1995 as having 2 guillemots present, although it seems 

unlikely that the birds were nesting. The island is probably already over-topped by waves in winter 

storms, and there appears to be little or any habitat available for seabirds other than loafing 

individuals. We consider it a Category 1 (most sensitive) island, but its status as a “nesting” island is 

questionable.

Scrag Island currently maintains a small colony of cormorants as well as nesting gulls, eiders, and 

guillemots. Although it tapers slowly to the east and west, the central portion of the island is greater 
24

than 10m above the current biological high tide line xvii

, and it supports permanent vegetation along 

its upper ridge lines. We regard it as a category 2 island (moderately sensitive) as it is likely to lose 

guillemot nesting habitat under even limited sea level rise, and current seal haul-out and bird loafing

ledges will be flooded. However, as mentioned above, the island’s tapered shape suggests that 

additional habitat will be created as the sea advances.

Green Island is the largest of the three islands in this cluster, and while portions of the island reach at 

least 10m above current sea level, its long low shape (Fig. 18) suggests that it is likely to lose 

significant area in the foreseeable future.

In spite of this however, the island is large enough that it seems likely that nesting habitat will remain 

available in all but the most catastrophic flooding scenarios, leaving it in a Category 2 status.

Figure 18. Green Island N. Shore.

Heron Island

Heron Island (44 06 02 N, 68 28 24 W), located 4.5 km SW of Swan’s Island, is the third most 

important “fee ownership” seabird island within Acadia National Park. It has traditionally supported 

large populations of nesting gulls and eiders, although as with other islands the seabird population 

has declined dramatically in recent years (Table 1). In 2012 we sighted 9 Bald Eagles on Heron and 

in 2013 we saw 5 immature eagles. In both cases the eagles were in areas that had supported nesting 

gulls. Heron is also unique in that it has a population of muskrat (Ondatra zibethicus) that was 

introduced during the mid-20th century.
25

Much of the island consists of a low marshy center surrounded by a high cobble sea-wall (Figs. 

19 a-c). Another prominent feature of Heron Island is the large glacial erratic boulders (Fig. 19d) that 

dot the landscape within the island’s core. In some cases these boulders support their own microflora, significantly different from the surrounding boggy landscape (Fig. 19e).

Figure 19. a) N. shore Heron Island, b) sea-wall, Heron Island, c) sea-wall on Heron Island (note flooded 

area behind the wall), d) glacial erratics within central area of Heron Island, and e) detail of glacial erratic, 

Heron Island.
26

Models of likely flooding scenarios (Fig. 20) suggest that Heron is a Category 2 island –moderately 

susceptible to sea level rise.

Figure 20. Flood models for Heron Island.

The island’s size (approx. 21.0 ha) and elevation ensure that at least some nesting habitat will remain, 

even under the highest sea-level rise scenario, however we feel that this estimation may be overly 

optimistic for the following reasons: 1) the central portion of the island is currently protected by 

medium sized cobble sea-walls that are likely to be breached by large storms (there is already some 

evidence of over-topping in places); this sea-wall currently provides most of the available nesting 

habitat for gulls. 2) Guillemot nesting areas in portions of the sea-wall made up of larger stone slabs 

are likely to be impacted early and by even relatively minor increases in sea-level. Because of the 

overall construction of the island, there is no suitable additional habitat to which birds can retreat. 3)

The center of the island is already largely swampy, with numerous channels excavated by the 

resident muskrats. While there are still sufficient drier areas to permit nesting by eider ducks, as 

water intrusion increases, these areas may flood more rapidly than would be expected in rockier 

terrain. Vegetation structure is likely to be affected as the swampy areas become more brackish, and 

this may further reduce available eider nesting habitat.

Great Spoon Island

Great Spoon (44 02 31.5 N, 68 33 26.6 W), located 3.36 km E of Isle au Haut, is a park easement 

island, and at approx. 29m maximum elevation xviii, is the highest island in our study (Fig. 21a).
27

In spite of this comfortable elevation, taken on the island’s Northwestern peak, we rate Great 

Spoon a Category 2 island (moderately susceptible to flooding). At present, the island consists of 

three distinct “units” –a vegetated upland, well beyond the reach of even catastrophic flooding, 

and presently occupied by a few nesting gulls; a marshy lowland, protected by a high cobble seawall to the North (Fig. 21b, see also background of Fig. 3), at or at most slightly above the 

present biological high tide line, that is used by nesting eiders; and a low rocky spit (Fig. 22a and 

b), that extends to the Northeast. This latter portion of the island forms the “handle” to the 

eponymous “spoon” and is only connected to the rest of the island at low tide. This region 

provides nesting habitat to most of the island’s remaining population of gulls as well as a 

transitory nesting colony of terns.

Figure 21. a) Great Spoon from north, showing highest elevation and a portion of the cobble berm (left), 

and b) cobble berm on northern side of Great Spoon (note adult Bald Eagle perched immediately to the 

right of the driftwood pile).
28

Figure 22. a) Northeastern spit on Great Spoon, from the island peak (note seawall and partially flooded 

marshy area in foreground), and b) south face of Great Spoon sea-wall (note storm-line half way down).

Great Spoon was a major nesting colony for both Herring and Great Black-backed gulls as recently 

as 2008, with over 300 nests of each species reported present. In addition, the island was known to 

provide nesting habitat for over 400 Eider ducks, Black guillemots, and was periodically colonized 

by small groups of Arctic and Common terns (Sterna paradisaea and S. hirundo). As with other 

islands in this survey, seabird populations have declined significantly in recent years. Three to five 

Bald eagles were seen on the island in 2012 and 2013.
29

Our flood models (Fig. 23) suggest that in the event of even minor increases in sea-level, much of the 

marshy wetland area will be completely flooded, eliminating prime eider nesting habitat. This 

process will be accelerated and enhanced if the cobble sea-wall is breached by an increase in storm 

intensity. It seems likely however that, given the overall size (approx. 20 ha) and slope of the island, 

at least some new habitat is likely to develop ahead of the rising sea. The bulk of the main island will 

remain intact in even the most severe projections of sea level rise, with little change to the island’s 

southern shores, whose high cliffs and rock crevices provide nesting sites for Black guillemots and a 

few remaining gulls.

The greatest obvious impact will be to the northern “spoon handle” which seems likely to be 

broken up into a series of much smaller ledges, some of which are likely to be over-topped by 

moon tides and/or summer storms. Because this area is currently the region most heavily 

occupied by gulls, and the only region in which terns have been seen nesting, it is of particular 

concern.

Figure 23. Flood models for Great Spoon Island. Note that the northern “handle” is currently connected to 

the main island only at low tide.
30

Little Spoon

Little Spoon (44 02 18.33 N, 68 34 16.34 W), located 2.45 km E of Isle au Haut, is a park easement 

island and a significant nesting area for gulls, eiders, and guillemots. The island’s relatively high 

sides (Fig 24a), rocky composition, and overall area (approx. 9 ha) cause us to place it into category 

3 (least sensitive) in regards to concern over the effects of sea-level rise. Gulls and eiders were found 

nesting over much of the island, while guillemot nests were common in the rocky areas at the eastern 

end of the island (Fig. 24b).

Figure 24. a) Northwestern end of Little Spoon Island (note high sides, basalt/granite composition, and 

tapering of island’s extremities), and b) close-up of northeastern shoreline of Little Spoon Island. Gulls, 

including both Herring and Great Black-backs were found nesting in short vegetation along the ridge line, 

whereas Black guillemots nested in rocky crevices, particularly in the eastern end.
31

Our flood models (Fig. 5c) reinforce the notion that Little Spoon is relatively safe from the effects of 

sea level rise at this time.

Figure 25. Flood models for Little Spoon Island.

Even under a worse-case scenario, significant portions of the island will remain, although the 

northern end may be split into one or two separate ledges. As with other islands, guillemot habitat is 

likely to be most heavily impacted, although there is sufficient interior relief to the island to allow the 

possibility of new nesting areas developing as the sea advances.
32

White Horse and Black Horse

White Horse (44 01 53.3 N, 68 34 07.7 W) located 2.95 km E of Isle au Haut (Fig 26a), and Black 

Horse (44 01 37.4 N, 68 34 32.07 W) located 2.62 km E of Isle au Haut (Fig 26b), are both easement 

islands. While both have occasional records of nesting seabirds, neither can be regarded as 

particularly significant at this time.

Figure 26. a) White Horse Island, and b) Black Horse Island.
33

Both islands are small (0.28 ha for White Horse; 0.55 ha for Black Horse), are relatively high sided 

and consist of consolidated rock. As such they are relatively resistant to erosion. Flood models (Fig. 

27) suggest that even drastic sea level rise will not cover much additional area on Black Horse, 

though the island’s long, thin shape and exposed location more-or-less ensures that there will be an 

increase in spray, which may make what limited habitat exists untenable in future. In any case, 

neither island has substantial populations of nesting seabirds. We list both islands as Category 1 

(most sensitive to sea-level rise).

Figure 27. Flood models of Black Horse Island.

Shabby Island

Shabby Island (44 10 00.88 N, 68 33 31.45 W), located 4.7 km W of Swan’s Island, is a park 

easement island containing populations of gulls, guillemots, cormorants and eiders. The island is 

small (1.45ha) but with relatively high-sided, sloping shorelines (Fig. 28a) consisting of consolidated 

ledge (Fig 28b). As such we rate it a Category 2 island (moderately impacted). Gulls were nesting in 
34

all parts of the island in 2013, including on the sandy shoreline within 2m of the biological high tide 

line. Cormorants were restricted to the rocky point at the islands southwest end. We noted with some 

concern that although when we circled the island for our initial count the cormorants appeared to be 

“sitting tight” as if incubating eggs or young chicks, when we actually examined the nests they 

contained neither eggs nor chicks. There was no obvious sign of predation other than a single broken 

egg-shell, but we found one predated adult cormorant a little distance from the nest site. An 

immature Bald eagle was roosting on the northern ledge when we approached and circled the island 

while we counted seabirds. We located 8 active Eider nests on the island, a marked decline from 

previous estimates. We also recorded Black guillemots in the water around the island but made no 

effort to make a formal count for fear of further disturbing the other species present.

Figure 28. a) Shabby Island from the East, and b) Shabby Island close-up of shoreline.
Flood modelling (Figure 29) supports our general classification of Shabby Island’s level of 

vulnerability. Low to moderate increases in sea-level will reduce the island’s total area, but even in 

our most catastrophic scenario, significant nesting area remains.

Figure 29. Flood models of Shabby Island. Ledges to northwest are already largely submerged at 

extreme high tide.

37

Conclusions

While the majority of Acadia National Park’s island properties and easements do not support nesting 

seabirds at this time, the park owns in fee, or has an interest in, several historically important nesting 

colonies. All of these islands are likely to undergo some degree of change in the next century as the 

climate changes and sea level continues to rise. At the same time, other more immediate forces are 

already having an enormous impact on nesting seabird populations, both within the park and 

throughout much of the coastal North Atlantic. Regionally, the recovery of Bald Eagles seems to be 

playing a major role in reducing the number of nesting gulls, cormorants, and eiders in the Gulf of 

Maine. We were struck by the large numbers of eagles that we saw in close association with every 

island that we surveyed over the past three years. Eagles prey on both chicks and adults, and also 

disrupt entire colonies, making nests more vulnerable to corvids and other smaller predators. We 

urge the Park Service to engage in regular monitoring programs on park islands to assess the longterm effects of the loss of seabirds on both regional populations and local vegetation. In addition, we 

were concerned by the lack of adequate signage on many islands. The steadily increasing sea-kayak 

traffic in coastal waters is likely to have an ever greater impact on nesting birds as kayakers take 

advantage of recreational opportunities and land on sensitive islands. It would be advisable to post all 

nesting islands with large signs readable from the water indicating that the island is closed from May 

through August.

In terms of response to sea level rise, it is hard to imagine mitigation strategies that would be either 

cost-effective or in keeping with current park management principles. Construction of sea-walls, 

armoring cobble berms or back-filling low-lying areas on islands would be enormously disruptive in 

every case, and would be prohibitively expensive. In addition it is unclear whether it would have the 

desired results in terms of maintaining seabird populations, and it is doubtful whether such action 

would produce measureable results given other changes occurring in the surroundings.

Management responses to sea-level rise and changes in seabird populations and nesting sites include 

several potential strategies. Here, we explore three strategies: First of all, educating the general 

public as to the effects of climate change and sea level rise is a vital strategy. This can be done at 

multiple levels: additional curricula can be prepared for High School and K-8 classroom presentation 

on the relationships between seabirds, islands, and climate change and the role of the NPS in 

safeguarding this resource; informational brochures and posters can be developed and made available 

to Park visitors emphasizing the broader role of Acadia in resource conservation that goes beyond the 

Mt Desert island core areas of the Park; and finally Ranger-lead “campfire talks” at campgrounds and 

the Visitor Center can incorporate information on the Park’s role in seabird conservation and 

management.

Second, regular and frequent (minimum every three years) of existing nesting colonies can provide 

managers with information on long-term trends. This can be done either independently or in 

collaboration with other State and Federal agencies. Because Acadia has relatively few seabird 

islands, a regular survey, once established, could be done relatively cheaply and would provide a 

valuable baseline for measuring change. Ideally, such a survey would include both censuses of 
38

nesting seabirds and also regularly updated geo-referenced photographs that would permit long-term 

comparisons of shoreline and habitat conditions. A single person should be designated to oversee 

survey methodology and regular up-dating of databases.

Finally, the National Park Service might consider assessing current non-Park islands for acquisition 

as future seabird colonies, perhaps in partnership with other Federal, State, or private organizations.

The NPS’ strategies of resource protection and monitoring could be a valuable addition to work done 

by other organizations, and could serve as an important “low intervention control” from the more 

active management schemes imposed by other agencies. Ideally, new islands would be steep sided, 

with significant consolidated ledge material so as to avoid erosion, they should be at least 0.5 ha in 

size, and should be located far enough from major land-masses so as to reduce the likelihood of the 

immigration of terrestrial predators. 

While in the end we are faced with the problem of King Canute –the water will rise no matter what 

we say - we have the opportunity to learn a great deal in the process of watching this long tide come 

in. It is my hope that this report is but the first step in that learning process.
39

Literature Cited 

i Drury, W. H. 1973. Population changes in New England seabirds. Bird-banding 40:267-313. See 

also: Erwin, R. M., and C. E. Korschgen. 1979. Coastal waterbird colonies: Maine to Virginia, 

1977. An atlas showing colony locations and species composition. U.S. Fish and Wildlife 

Service, Biological Services Program, FWS/OBS-79/08. 

ii http://netapp.audubon.org/iba (accessed 1September 2015)

iii Kelley, J. D. F. Belknap, G. L. Jacobson Jr. and H. A. Jacobson.1988. The morphology and origin 

of salt marshes along the glaciated coastline of Maine, USA. Journal of Coastal Research 4:649-

666. See also: Donnelly, J. 2006. A Revised Late Holocene Sea-Level Record for Northern 

Massachusetts, USA. Journal of Coastal Research 22:1051-1061 for discussion of regional 

changes.

iv Spiess, A. and R. Lewis. 2001. The Turner Farm fauna: 5000 years of hunting and fishing in 

Penobscot Bay, Maine. Maine Archaeological Society, Augusta, ME. 

v Drury, W. H. 1973. Population changes in New England Seabirds. Bird banding 44:267-313.

vi Parris, A., P. Bromirski, V. Burkett, D. Cayan, M. Culver, J. Hall, R. Horton, K. Knuuti, R. Moss, 

J. Obeysekera, A. Sallenger, and J. Weiss. 2012. Global Sea Level Rise Scenarios for the US 

National Climate Assessment. NOAA Tech Memo OAR CPO-1. 

vii Anonymous 2010. Advancing the science of climate change. America’s climate choices. National 

Research Council. National Academy of Sciences Press. Washington, D.C.

viii

http://www.pivot.net/~cotterly/hurricane.PDF (accessed 1 September 2015). According to this 

report, between 1635 and 1996, Maine has been impacted by 45 major tropical storms. Of these 

28 have occurred later than Aug 23, well outside the breeding season of most seabirds.

ix Grinstad, A. J. Moore, and S. Jevrejeva. 2013. Projected Atlantic hurricane surge threat from rising 

temperatures. PNAS 110:5369-5373

x Erwin, R. M. and C. E. Korschgen 1979. Coastal waterbird colonies: Maine to Virginia, 1977. 

USFWS Biological Services Program FWS/OBS-79/08

xi

Anonymous 2010. Maine 2008 coastwise census for gulls and cormorants. Data summarized by 

Maine Coastal Islands National Wildlife Refuge. U.S. Fish and Wildlife Service, Millbridge, ME.

xii Allen, B. G. Mittelhauser, L. Welch, R. Houston, R.Schauffler, and M. Langois. 2012. Maine atlas 

of breeding seabird and coastal wading bird colonies: 1960-2011. Maine Natural History 

observatory Gouldsboro, ME.
40

xiii Todd, C,. and G. Matula. 2008. Delisting the bald eagle in Maine: An amazing success story. ME 

Dept. Inland Fisheries and Wildlife. Available at 

http://www.maine.gov/ifw/docs/BAEA_Delisting.pdf (accessed 1 September 2015).

xiv Bourget, A. 1973. Relation of eiders and gulls nesting in mixed colonies in Penobscot Bay, Maine. 

Auk 90:809-820. See also: Gotmark, F. 1989. Costs and benefits to eiders nesting in gull 

colonies: A field experiment. Ornis Scandinavica 20:283-288

xv Gross, A. 1945. The present status of the great black-backed gull in Maine. Auk 62:241-256.

xvi See for instance Birds of North America No. 675. Ronald G. Butler and Daniel E. Buckley. 2002. 

Black Guillemot, Cepphus grylle. (Charadriiformes : Alcidae). 32 pp. A.O.U. CHECK-LIST p. 

211.1

xvii

http://www.ngs.noaa.gov/cgi-bin/ds_desig.prl (accessed 1 September 2015)

xviii

http://www.ngs.noaa.gov/cgi-bin/ds_desig.prl (accessed 1 September 2015)
The Department of the Interior protects and manages the nation’s natural resources and cultural heritage; provides scientific 

and other information about those resources; and honors its special responsibilities to American Indians, Alaska Natives, and 

affiliated Island Communities.

NPS 123/130051, October 2015
National Park Service

U.S. Department of the Interior

Natural Resource Stewardship and Science

1201 Oakridge Drive, Suite 150

Fort Collins, CO 80525

www.nature.nps.gov

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