The Unsuspected Decline of the Herring Gulls

Kent Island has the densest population of gulls that I have ever seen in one place, and when we first pulled in to the Island on the Susannah Kent, they welcomed me with their enormous racket. The large number of gulls in the sky and the abundance of their nests gave me the initial impression that the population was thriving. One night after dinner, during one of the conversations of days past that follow a good meal, Nat Wheelwright, a former BSS Director, revealed that the Herring Gull population on the Island is actually in decline. He recalled that one visitor who hadn’t been to the Island for forty years asked, “Where are all the gulls?” when he arrived. Nat pointed out the quietness of the evening, saying that the clamor that is now largely confined to the shore and to the South End used to be inescapable everywhere.

The scientific record of the gulls supports these more qualitative measures of abundance. Alfred Gross, a Bowdoin ornithology professor, conducted a census of the gulls in 1940 that found 11,000 pairs nesting on the South End, and estimated at least 25,000 gulls on the Island during peak breeding season. Gross postulated that the colony was the largest on the Atlantic seaboard. His son, Bill Gross, the first Director of the Bowdoin Scientific Station, remarked that the gulls were under government protection because they were on the verge of extinction, but now were over-populating Maine and the Maritimes. Fishermen resented the gulls for stealing bait from boats, and on Kent Island, half-starved gulls were preying upon savannah sparrows, petrels, and eider chicks. In response to the over-population problem, the United States Biological Survey began making annual cruises along the Maine coast to destroy gull eggs by piercing them with a needle, rendering them infertile without the gulls being the wiser.

In a stark contrast to the earlier abundance of gulls, a 1983 study estimated only 5,000 nesting pairs on Kent Island, and references Herring Gull declines in New England and the Maritimes. A later census of the colony in 1989 found 1,441 nesting pairs, and high egg and chick mortality. Possible causes of the gulls’ low reproductive success included bad weather and visitation by local “eggers” who took between 50 and 100 eggs on several weekends, in violation of the Migratory Birds Convention and Act. There is a long tradition of egging in the Bay of Fundy, and even Niko Tinbergen, champion of the Herring Gulls and author of The Herring Gull’s World, proclaims gull eggs “an excellent food.” This practice has consequences beyond the obvious reduction in the number of eggs, because the disturbance increases the gulls’ nest abandonment and cannibalism, furthering the decline of the colony. While egging is a dying pastime on Grand Manan, a few eggers occasionally come to Hay Island and take from nests with one or two eggs. Gulls typically lay three eggs in succession and do not begin to incubate them until the third “insurance egg” is laid. Despite the lack of egging on Kent Island and the relative stability of the gull habitat, the population has probably decreased by an order of magnitude in the past fifty years. Damon told me that the most likely causes of the decline are the closing of landfills, and the collapse of the groundfish fishery, which used to produce large amounts of bycatch that the gulls fed on. The Herring Gulls that return to Kent Island to breed every summer are dispersed all over North America the rest of the year, and changes in their other habitats may also play a role in the decline.

My first impression of the abundant Herring Gull population on the Island is a good example of how baselines skew our perception of the world. I had never seen so many gulls in one place, and therefore assumed that the population was thriving, while gull censuses from scientific studies showed a decline over time. Long-term data is an extremely important part of environmental science, because otherwise policies may be based on a baseline that makes false assumptions about a population’s health. These misguided policies can have drastic consequences, as evidenced by the collapse of the groundfish fisheries.

Sources:

Gross, A.O. 1940. The migration of Kent Island Herring Gulls. Bird-Banding 11: 129-155. (BSS Contribution no. 7)

Cannell, P.F. and Maddox, G.D. 1983. Population Change in Three Species of Seabirds at Kent Island, New Brunswick. Journal of Field Ornithology 54 (1): 29-35.

Hébert, P.N. 1989. Decline of the Kent Island, New Brunswick, Herring Gull, Larus argentatus, colony. Canadian Field-Naturalist 103: 394-396.

W.A.O. Gross. 1936. Kent’s Island, Outpost of Science. The American Museum of Natural History. Natural History 37 (4): 195-210.

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