Restoration of a Multi-Species Seabird Colony

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Biological Conservation 90 (1999) 175±181 www.elsevier.com/locate/biocon

Restoration of a multi-species seabird colony

John G.T. Anderson*, Catherine M. Devlin Island Research Center, College of the Atlantic, 105 Eden St., Bar Harbor, ME 04609, USA

Received 1 January 1996; received in revised form 6 September 1998; accepted 12 January 1999

Abstract Nesting herring and great black-backed gulls (Larus argentatus and Larus marinus) were removed from a recently abandoned tern (Sterna sp.) colony through a combination of poisoning and shooting. Following gull control, all three species of tern that had nested in the colony prior to the arrival of the gulls returned and nested in increasing numbers. In addition to the restoration of the terns, removal of the gulls led to colonization and/or signi®cant increases in populations of four other seabirds. Gull numbers were greatly reduced by initial poisoning eorts, but continued immigration from surrounding colonies has required an on-going program of shooting to eliminate territorial birds nesting in areas utilized by terns and other species. In situations calling for active management we advocate rapid, focused intervention, and stress the importance of inter-organizational cooperation, and an active program of public education. # 1999 Elsevier Science Ltd. All rights reserved. Keywords: Restoration; Predator control; Terns; Gulls

1. Introduction gull had continued to expand, populations of other seabirds were once more in decline. The suspected primary cause of The impact of increasing numbers of large gulls, par- the decline was predation and/or territorial behavior by ticularly herring gulls (Larus argentatus) and greater the large larids. The population of herring and great black backed gulls (L. marinus) has been of concern in black-backed gulls was supported by the presence of Britain, Europe, and the eastern United States for much large open land®lls along the entire New England coast of the latter part of this century (Gross, 1951; Thomas, as well as the disposal of ®sheries by-catch. 1972; Drury, 1973; Coulson et al., 1982; Blokpoel and By the 1960s the bulk of the remaining arctic (Sterna Spaans, 1991; Vauk and Pruter, cited in Spaans et al., paradisaea), common (S. hirundo) and roseate (S. dou- 1991). Gulls have been implicated in the spread of dis- gallii) terns were concentrated on islands containing ease, collisions with aircraft, and predation on other manned light-stations. Coast Guard personnel, con- species of waterfowl. It is with this latter eect and its cerned about the impact of bird droppings on their remediation that we are concerned here. water sources, tended to shoot or otherwise discourage The Gulf of Maine in eastern North America contains herring and great black-backed gulls from nesting on over 6000 islands, many of which have been historical islands with light-stations. Terns and other seabirds, nesting sites for seabirds. In the late 19th century a which were less likely to roost near human-occupied combination of hunting pressure and extensive use of structures, were largely ignored, with the result that the coastal and outer islands by ®sher-folk lead to the lighthouse islands became de facto refuges (Drury, almost complete disappearance of most seabirds 1973; W.H. Drury, pers. comm.). including gulls (Larus) and terns (Sterna). Changes in Automation of the light stations during the 1960s and land-use practices and the elimination of plume hunting early 1970s was followed by the colonization of the resulted in a widespread recovery of most species that lighthouse islands by large gulls and the collapse of tern lasted into the mid-1940s (Drury, 1973, 1974). colonies. Discussion among private, federal and state By the 1950s it became apparent that while the popu- conservation organizations during the 1970s and early lations of the herring gull and the great black-backed 1980s lead to a general agreement on the need to re- establish populations of terns and other seabirds at a variety of sites along the north-eastern seaboard of the * Corresponding author. United States. Following an initial success (Kress,

1983), gull removal programs have been initiated on 2.2. Seabird censuses nine islands in the Gulf of Maine. In this study we report on the eect of gull control on an island coop- Since 1985 Petit Manan Island has been searched eratively managed by the US Fish and Wildlife Service thoroughly for nesting terns during the peak laying time and the Island Research Center at the College of the period. The search is conducted by four to six research- Atlantic in the state of Maine. We compare the changes ers walking in line at arms' length apart. Each nest is in nesting numbers on this island to other seabird nest- marked with a numbered 10 cm wooden stake. At the ing islands in the Gulf of Maine. conclusion of the count, one researcher walks back through the colony in a zigzag pattern at right angles to 1.1. Study site the route of the original count. This individual records the number of marked and unmarked nests encoun- Petit Manan Island, Washington Co. ME (Lat. 44220 tered. The resulting ratio (typically between 0.05 and Long. 67520) is located approximately 3 km south of 0.07) is applied to the initial total as a `correction factor' Petit Manan Point. It is joined at low tide to neighbor- for missed nests. ing Green Island by a broad cobble bar. The light sta- Laughing gulls have nested on Petit Manan at least since tion on Petit Manan was manned from the early 19th the early 1960s (Hatch, 1970, 1975). Prior to 1989, counts century until 1975, when permanent human occupation of laughing gulls consisted of transects taken through areas of the island ended. Petit Manan is part of a National of presumed maximal density, with extrapolations provid- Wildlife Refuge, administrated by the United States ing an estimate for the island as a whole. Since 1989, all Fish and Wildlife Service. Green Island is owned by the areas of the island have been searched for nests. State of Maine and administered by the Department of With the exception of six black guillemot nests loca- Inland Fish and Wildlife. Petit Manan and Green Island ted in 1995, Green Island has only provided nesting sites have traditionally been managed as a single unit. for common eiders (Somateria mollissima), herring gulls The Petit Manan/Green Island archipelago was an and great black-backed gulls. Data for eiders on the two important nesting site for terns since at least 1931 islands has traditionally been combined in reports, but (Drury, 1990). After human occupation of the island the majority of eiders seem to have always nested on ceased in 1975, increasing numbers of herring and great Green Island. Common eider duck nests were counted on black-backed gulls moved onto Petit Manan and dis- Petit Manan Island in mid-June as part of the laughing placed the tern population in a fashion seen elsewhere in gull census. Green Island was censused in late May New England (Drury, 1965, 1974). A census in 1983 approximately every 3 years. Total nests are reported as (W.H. Drury, pers. comm.) revealed that only two arc- the sum of the number of nests found on both islands. tic terns and no common or roseate terns were nesting Nesting burrows of black guillemots and Atlantic on the island, compared to over 1500 pairs (all three puns (Fratercula arctica) were located through inten- species combined) reported in the late 1960s. sive searches of the rocky berm surrounding the island. The number of herring and great black-backed gulls nesting on Petit Manan and Green Islands was recorded 2. Materials and methods in the course of poisoning sweeps and/or censuses of each island in late May or early June. 2.1. Gull control Comparative data of seabird colonies on other islands in the Gulf of Maine were obtained from Erwin and In 1984 the US Fish and Wildlife Service initiated a Korschgen (1979) and the State of Maine Department gull-control program. The avicide DRC1339 was placed of Inland Fisheries and Wildlife. in gull nests on both Petit Manan and Green Islands (Thomas, 1972; Woronecki et al., 1989; Blodget and Henze, 1992). Poisoning on Petit Manan ceased after 3. Results 1984; however it continued yearly on Green Island through 1987 and a ®nal poisoning was conducted on 3.1. Gull control Green Island in 1990. No further management activity has been conducted on Green Island except for periodic A total of 551 herring and 117 great black-backed censusing. Every year, since 1985, one to four pairs of gulls were killed in 1984 (Fig. 1). This dramatically herring or great black-backed gull pairs have attempted reduced the number of gulls nesting on Petit Manan, to nest on Petit Manan. Birds attempting to nest or seen but a core population of 150±200 pairs persisted on actively harassing terns, black guillemots (Cepphus Green Island (Fig. 2). In 6 years of poisoning a total of grylle) or laughing gulls (Larus atricilla) have been kil- 1984 baitings were applied, leading to the recovery of led with a 0.22 ri¯e. Gulls loa®ng on the lower intertidal 1084 gull carcasses. Of these 752 (69%) were herring of Petit Manan have been left undisturbed. gulls and 332 (31%) were great black-backed gulls J.G.T. Anderson, C.M. Devlin / Biological Conservation 90 (1999) 175±181 177

Fig. 1. The number of herring and great black backed gulls collected on Petit Manan and Green Islands. Collection prior to 1991 was through a combination of poisoning and shooting. Following 1990 only shooting has been employed.

Fig. 2. Number of large gulls nesting on Green (hatched bars) and Petit Manan Islands (solid bars). Diamonds indicate years when no census was conducted. Data from US Fish and Wildlife Service Refuge records.

(Drennan et al., 1986; Folger and Drennan, 1988; Petit increased until 1996, when they suered a decline. The Manan Refuge ®les). Over 11 years approximately 40 laughing gull population of Petit Manan has increased individual gulls have been shot on Petit Manan. by a factor of 3 since the removal of large gulls (Fig. 4). Data for eiders are sparser than for other seabirds. 3.2. Terns and other seabirds However, numbers for Petit Manan and Green Island combined have increased from 62 nesting females at the Terns returned to Petit Manan within two weeks of onset of gull control in 1984 to 1037 in 1994. the 1984 gull removal (Drennan et al., 1986), and have Black guillemot numbers increased from 16 pairs in nested on the island in all subsequent years [Fig. 3(a)±(c)]. 1984 to a high of 156 in 1995. There are no records of Arctic tern numbers quickly returned to the levels puns in the vicinity of either Petit Manan or Green observed immediately prior to the arrival of large gulls Island prior to 1984. Occasional puns were seen loaf- to the colony, but have never regained the all-time highs ing in 1984, and the ®rst nest was recorded in 1986. recorded in the 1960s. Common tern numbers increased Starting in 1991 the number of puns breeding on Petit steadily until the early 1990s. Roseate tern numbers Manan began to increase, reaching a high of 17 in 1998. 178 J.G.T. Anderson, C.M. Devlin / Biological Conservation 90 (1999) 175±181

Fig. 3. The number of roseate, common, and arctic terns breeding on Petit Manan Island. Diamonds indicate no available data. Numbers prior to 1989 from Drennan et al. (1986), Folger and Drennan (1988), and Refuge records

Fig. 4. The number of laughing gulls nesting on Petit Manan Island. Diamonds indicate years in which no count was conducted

The ®rst puns banded as chicks on Petit Manan Atlantic (Coulson et al., 1982; Kress, 1983; Coulson, returned to the island in 1994 and bred in 1996. 1991; Anderson and Devlin, 1996). On Petit Manan Island the initial applications of DRC1339 in 1984 cou- 4. Discussion pled with an on-going human presence each summer has essentially eliminated nesting herring and great black- Gull control has been used as a management techni- backed gulls. Gull control on nearby Green Island que on many seabird colonies on both sides of the has stabilized the number of nesting gulls but has failed J.G.T. Anderson, C.M. Devlin / Biological Conservation 90 (1999) 175±181 179 to rid the island of a base population of approximately vegetation on the island. As the number of laughing 120±150 pairs. During years in which active gull control gulls has increased over the course of the management occurred on Green Island very few gull chicks ¯edged, program the laughing gulls have spread into less densely thus the continued settlement of gulls on Green Island vegetated areas. Part of this change in distribution may and the limited nesting attempts on Petit Manan must be due to vegetation changes, but it seems likely that the be due to immigration from other colonies (Coulson, elimination of large territorial gulls has freed the laugh- 1991). Only the continued presence of the research team ing gulls to make greater use of more of the island. has kept Petit Manan relatively free of large gulls. Laughing gulls in Maine nest only on managed islands. In terms of its primary goal of the restoration of a Common eider ducks appear to have bene®ted from the viable tern colony on Petit Manan Island, the gull con- reduction in predatory gulls on Petit Manan and Green trol project has been an unquali®ed success. From near Islands. It should be noted, however, that although eiders collapse in 1983 total tern numbers in the colony have suer severe chick predation from large gulls, evidence increased to a record high of over 2000 pairs in 1995. In from Finland (Olson, 1951, cited in Bourget, 1973) sug- the early 1970s, prior to the arrival of herring and great gests that it may be bene®cial for eiders to nest on islands black-backed gulls on the island, common tern numbers that have at least some gulls capable of driving away increased and arctic tern numbers declined leading to crows and ravens (Corvus sp). Corvids are extremely equal proportions of the two species by the mid-1970s. eective predators on eider eggs, and it is possible that the In the ®rst few years of management, arctic terns out- loss of some chicks to gulls is preferable to the loss of an numbered common terns, but by 1988 the common tern entire clutch of eggs to a raven. Ravens have attempted to had become dominant, a status they retain through the nest on four occasions on Petit Manan since the gulls present day. This change in relative proportion may be were removed, and have preyed on eider nests, but they part of a general northward shift in the arctic tern's have not nested on Green Island. Eider ducks appear to nesting range (Nisbet, 1983). use small coves along the eastern and southern edge of One reason for the decline in nesting arctic terns on Petit Manan as relatively gull-free nurseries' prior to Petit Manan may be the establishment of another tern dispersal to the mainland bays. Creches of 5±15 eider colony in more suitable arctic tern habitat. In 1984 the chicks are regularly observed around Petit Manan, these National Audubon Society and the US Fish and Wild- are seldom seen near Green Island. life Service removed gulls from a large segment of Seal Although small numbers of black guillemots had been Island in Penobscot Bay, approximately 90 km west of known to nest on Petit Manan prior to the collapse of Petit Manan and 32 km oshore (Kress, 1994) as part of the tern colony, their numbers have increased sub- a project to attract Atlantic puns and other seabird stantially under the management program. The lack of species to the area. In 1989 arctic terns ®rst nested on deep crevices or suitable soil for burrowing makes these Seal Island, and numbers increased to a high of birds vulnerable to predation by loa®ng gulls. We sug- approximately 500 pairs in 1995. Arctic terns are known gest that black guillemots are willing to nest in less sui- to favor outer islands (Hawksley, 1957) and the initial table substrate on the island, where protection is development of this colony, which had not been active provided by the management team, in preference to since the early 1950s, could only come at the expense of suering higher levels of interference and predation on other nearby colonies such as Petit Manan. unmanaged islands. The roseate tern's status as both a state and US fed- The establishment of nesting Atlantic puns on Petit erally listed endangered species has been a signi®cant Manan may be part of a larger southward expansion of component of management concern. Roseate tern num- this species' range. Some banded birds from the Audu- bers on Petit Manan Island increased through 1993. In bon Society's reintroduction program in Penobscot Bay 1994 and 1995 nesting pairs of herring gulls were found (Kress, 1982) have been seen on the island, however the in the dense vegetation at two sites used in previous proportion of these birds has declined signi®cantly in seasons by small clusters of six to nine pairs of roseate recent years. A number of islands with apparently more terns. Although the gull nests were destroyed upon dis- suitable habitat exist between the nearest naturally covery, the gulls were present during the peak nesting occurring Atlantic pun colony on Machias Seal Island, period for terns, and no birds settled in the areas. This Canada and Petit Manan, yet only Petit Manan has been example illustrates the potential impact of small num- selected as breeding site. As with the black guillemots, bers of territorial gulls on the restoration eort. the elimination of predatory gulls seems to be a bene®t Some of the increase in laughing gulls may be due to that outweighs the advantage of better nesting substrate. recruitment from expanding colonies in southern New England, but it is also likely that local ¯edging success 4.1. The eect of management on nesting seabirds has bene®ted from reduced predation. Prior to the removal of herring and great black-backed gulls, the It is important to dierentiate between changes laughing gulls on Petit Manan nested in the densest directly caused by management activities and changes 180 J.G.T. Anderson, C.M. Devlin / Biological Conservation 90 (1999) 175±181 that are part of larger regional trends that may mimic, pool data, compare techniques, and to plan future stra- amplify, or mask presumed management outcomes. tegies. Management and research decisions are usually Islands vary signi®cantly in area, history, vegetation, reached by consensus among the interested parties. A topography, and distance from shore and other islands. Gulf of Maine Tern Management Plan was developed A precise control' for any management treatment is as a result of the on-going dialog among members, and impossible. large portions of the Plan have been adopted into the Populations of all species discussed in this paper have State of Maine ocial planning guide. This sort of col- changed during the course of the management program. laboration is of increasing importance as we recognize Some of these changes are doubtless occurring inde- the trans-boundary nature of most conservation issues. pendently of our eorts. In 1977 all major seabird islands in the northeastern United States were censused by the US Fish and Wildlife Service (Erwin and Acknowledgements Korschgen, 1979). These estimates and subsequent sur- veys by the Maine Department of Inland Fisheries and The authors would like to thank Tom Goettel, Gerry Wildlife (J. Anderson, unpublished data) provide Atwell, Maggie Anderson, and the sta of the Petit detailed census numbers for islands before and after the Manan Wildlife Refuge for many years of active colla- commencement of management eorts. boration, ®nancial and logistic support and Between 1977 and 1998 the total number of arctic encouragement. Jeremy Hatch provided advice, com- terns nesting on Maine islands, excluding Petit Manan, ments, and information on the history of the island. increased from 940 to 2122 pairs. Common tern num- Brad Allen of the State of Maine Dept. of Inland Fish- bers increased from 1395 to 5447 pairs, and roseate eries and Wildlife provided comparative data on terns increased from 55 to 245 pairs. The total number guillemots. Steve Kress has provided an invaluable role of common tern colonies declined from 24 to 21, while as coordinator of the Gulf of Maine Tern Working arctic tern colonies declined from 9 to 7 and roseate tern Group, and provided unpublished data on Eastern Egg colonies increased from 3 to 4 (Koch, 1998). In 1998 Rock. We would also like to acknowledge David Fol- over 95% of all the arctic terns, 90% of common terns ger and Matt Drennan, Andrea Roberto, Glen Mittel- and all roseate terns nested on colonies subject to gull hauser, Rick Schauer, Artie Fleischer, and over a removal. dozen dedicated interns who have served heroically in Laughing gulls increased from 231 pairs on six colo- fog, rain, and sun to keep the project going. Karen nies in 1977 to 1517 pairs on three colonies in 1998. All Anderson and Mary Gene and Jim Devlin provided tea three colonies in 1998 were on islands from which large and sympathy and kept the home ®res burning. Sarah gulls had been removed. For 15 islands for which com- Cole provided valuable comments on early drafts of this parative data is available, the total number of common manuscript. Funding was provided by the US Fish and eider ducks declined from 2908 to 2188 during the per- Wildlife Service, The Frank M. Chapman Fund of the iod 1977±1994. The greatest decrease for any one island American Museum of Natural History, the Garden was 687 nests and the greatest increase was 146 nests. Club of Mt. Desert Island, and the College of the None of these islands were managed for gulls. Atlantic Guillemot Fund. This paper is dedicated to the Data on black guillemots are fragmentary and subject memory of William H. Drury Jr., without whom none to wide margins of error, but for 38 unmanaged islands of the work described here would have been possible. for which comparative counts are available from both 1977 and 1994 changes ranged between 50 and +50 nesting pairs during the period of management on Petit References Manan. The two closest islands where the predominant Anderson, J.G.T., Devlin, C.M., 1996. Conservation biology and nesting seabirds are black guillemots, Jordan's Delight human ecology: umbrellas, ¯agships and keystones. Human Ecol- and Schoodic Island, increased by 50 pairs and ogy Review 3, 238±242. decreased by one pair, respectively (G. Mittelhauser, Blodget, B., Henze, L., 1992. Use of DRC1339 to eliminate gulls and pers. comm.; B. Allen, pers. comm.). Neither of these re-establish a tern nesting colony in Buzzard's Bay, Massachusetts. islands are subject to gull control. Nesting Atlantic Proceedings Eastern Wildlife Damage Control Conference 5, 212± 215. puns in Maine are found only on managed islands Blokpoel, H., Spaans, A.L., 1991. Introductory remarks: super- (Kress, 1994). abundance in gulls: causes, problems and solutions. 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