Ardea
Official journal of the Netherlands Ornithologists' Union

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Verbeek N.A.M. (1977) Comparative feeding ecology of Herring Gulls Larus argentatus and Lesser Black-backed Gulls Larus fuscus. ARDEA 65 (1-2): 25-42
Two morphologically similar and closely related gulls, Larus argentatus argenteus and Larus fuscus graellsii, breed in a mixed colony on Walney Island, England. The question is raised what the differences are, if any, in the feeding habits between the two species, and what the behavioural and morphological background is of these differences. I counted the proportion of each species in several flight lines leading away from and towards the gullery and I found that graellsii fed mainly in the sea, the cities, and the fields; argenteus fed more on dumps, in fish halls, harbours, and intertidal areas. These findings were confirmed by on the spot counts. The daily foraging rhythm of argenteus is much more influenced by the tides than that of graellsii. Larus fuscus graellsii has a smaller, more favourable wing loading than argenteus and this makes it more adapted to fly long distances, to dive for its food, to be a cleptoparasite, and it has preadapted it to exploit food in cities. Larus argentatus argenteus stays closer to the colony than graellsii, its wing loading, as compared with graellsii's does not favour quick action, and its intertidal feeding habit has preadapted it to feed on garbage. As each species exploits its old niche and also according to its ability a part of the man-made food supply, both species have increased in numbers.


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