Sea Birds at Great Duck Island
True seabirds spend the majority of their lives at sea, coming to land only to nest. Seabirds have very particular needs when it comes to nest sites. Because many are ground-nesters, with long incubation periods, they must find an area that is free of predatory mammals such as mink, fox, or coyote. At present Maine's 6000 +/- islands contain among them over 240 nesting islands that between them are temporary home to nearly half the U.S. seabirds breeding east of the Mississippi.
Great Duck island has served as a refuge for nesting seabirds for more than a century. Ironically the island was first recognized as a sanctuary for the then-endangered Herring Gull.
Herring gulls are the common "sea gull" of the greater North Atlantic region. In point of fact, they are not strictly "seabirds" at all, they spend the vast majority of their time along the shore line, and are also found in inland fresh water settings. On Great Duck Island they nest in seven major sub-colonies, ranging in size from 7 to several hundred pairs. Each pair maintains a breeding territory around its nest from which other birds are excluded. Gulls on GDI typically lay 3 eggs, which they incubate for somewhat over 3 weeks. Young gulls can fly approximately 6 weeks after hatching. They disperse along the Eastern Seaboard of the United States and Canada. So far we have had band returns from New Jersey and also from the Great Lakes, as well as from as close as Bar Harbor!
Herring gulls, like many other species of birds were driven close to extinction in the late 19th century by a combination of habitat disturbance, egging, and hunters serving the hat industry. Birds on Great Duck seem to have been spared in part because of the island's relative inaccessibility. In 2002 we estimated that approximately 1000 pairs of Herring Gulls nested on the island.
Major predators on the gull chicks and eggs include Bald Eagles, Ravens, and Crows. Black Backed gulls also eat chicks and eggs, particularly when the adult Herring gulls are disturbed and driven off their nesting territory by visiting humans.
Great Black-backed Gulls
This, the largest gull in the world, is a relative late-comer to Maine and to Great Duck Island. Black-backs only appeared along this coast in the early 1940's, the bulk of their population is well to the north. For unknown reasons, Black-backed gulls are slowly spreading south along the eastern seaboard of the United States. They are voracious predators and have displaced Herring Gulls and other seabirds from traditional nesting locations. At present we have approximately 35 pairs of Black-backed gulls on Great Duck, and are monitoring them closely for signs of negative impact on the island's other seabirds.
Black Guillemots are common along the periphery of Great Duck Island, where they nest under large boulders in the island berm. In 2002 we recorded 808 Guillemots around Great Duck. Our high count from the lighthouse tower was 395. Guillemots typically lay from one to three eggs, which they incubate in crevices along the shoreline. Typical food includes "red rock eels" which are actually not eels at all, but rather gunnels.
Guillemot chicks are a perennial favorite with members of the Island Research team, we band all chicks that we can reach, but band life in guillemots is low due to constant wear of the band on the rocky substrate of their nesting and roosting habitat.
Guillemots are close relatives of puffins and razorbills, both of whom breed in small numbers to the east and west of Great Duck and in vast numbers in the far north (the Atlantic puffin is probably the most common seabird in the North Atlantic, with population estimates as high as 14 million!). In Maine, Great Duck shares with Penobscot Seal Island the title of "largest guillemot colony on the eastern coast of the U.S."
Contrary to popular opinion, Great Duck Island is not named for the vast flocks of eider ducks that use the island's shoreline as a nursery, instead the island is named after the migratory Black Ducks (close relatives of Mallards) that stop off in the Slough of Despond every Autumn. Although our high count from the tower this year was 1,120 eiders in early June, we found fewer than 10 nests on the island — most of the females and chicks that come to Great Duck's intertidal are probably from nearby Little Duck Island, which has no history of permanent human settlement.
Eiders have a very short courtship period in late spring, after which the males move off-shore to exclusive "bachelor clubs" while the females seek out islands to lay their eggs. Eider nests are masterpieces of thermal insulation — the female eider lines the nest with a thick layer of down, and weaves a down coverlet for the top that serves to both insulate the developing embryos and camouflage the nest from predators. In the Far north, Eider nests are traditionally collected at the beginning of the season as filling for down coats, comforters, sleeping bags, etc. So long as the nest is only taken once, the female will rebuild it and continue incubation. In Maine and parts of Europe eiders are only found nesting on islands that have populations of Herring gulls or active human control of predators. There is evidence that the gulls serve as deterrents to crows and ravens, who would destroy a whole clutch if they were to come upon a nest.
Once hatching occurs the female eider leads the chicks away from the nest site and guards them in an extended "creche" along the rocky intertidal. Some females appear to abandon their chicks entirely, while others adopt "orphans" to form clusters of 20+ chicks. Contrary to studies at other islands, we have found little evidence of predation by gulls on eider chicks. In over 43 hours of observation of groups of eider females and chicks from the lighthouse tower we saw a total of 2 attacks by Black backed gulls, both of which were broken off without loss of a chick after an aggressive response from eider adults. We saw no attacks by Herring gulls. Of more concern is predation by seals, who have been appearing in increasing numbers around the south end of Great Duck over the past two field seasons.
Leach's Storm Petrel
This, the commonest, and yet the most mysterious of our island's residents, is the major focus of the Island Research Center's current research. Julia Ambagis estimated that 9297 +/- 6500 pairs of petrels nested on Great Duck in 2000. A more recent re-analysis of Julia's work suggests that the actual number may lie around 5000 pairs, well within her range of estimates. In either case, this makes Great Duck the largest petrel colony in the eastern US.
According to some stories, Petrels — also referred to as "Mother Carey's Chickens" — get their name from St. Peter's ability to walk on the waves. Strictly speaking petrels don't "walk" on water, but they dabble their feet while fluttering over the surface, stirring up plankton, which they then swallow and process into a protein-rich oil, which also gives their burrows a pleasant musky odor.
Petrels are not strictly nocturnal — they forage in daylight up to 200 miles off-shore, and can frequently be seen on foggy days in in-shore waters. Their habit of appearing along the coast immediately before bad weather is responsible for the "storm" component of their name. They only come in to the breeding colony after dark — usually between 10 p.m. and 4 a.m. They nest in shallow burrows that run 25 cm to over 1m in length and lay a single egg. Because both members of a pair may be away at sea for prolonged periods, the egg tends to be cooler than that of actively brooding species, and incubation takes much longer than in gulls or guillemots.
We have found petrel chicks in burrows as late as October, hence the reason for Great Duck's closure to visitation until mid-Autumn. Major predators on petrel adults, eggs, and chicks seem to be crows and ravens, who excavate burrows and devour whatever they may find.