The feeding habits of great black-blacked gulls, Larus marinus, and glaucous gulls, L. hyperboreus, in Iceland

Abstract

The feeding ecology of Great Black-backed Gulls (Larus marinlls) and Glaucous Gulls (L. hyperboreus) in Iceland was compared by means ofstomach analysis and field observations. Samples of gulls were obtained throughout the year at Bulandshofdi, western Iceland, during spring at Reykjavik, southwestern Iceland and in autumn at Sandvik,southwestern Iceland. Field observations were made throughout the year at Hvalfjordur, southwestern Iceland.

There is a considerable difference between food selection of the two species, the Glaucous Gull feeding largely on live animals obtained in the intertidal sea-shore, while the Great Black-back is a greater scavenger and a predator on birds and fishes, and depends more on nonfish refuse. However, both species feed extensively on various foods of irregular and/or periodic abundance when these are available in quantity, and usually to a similar degree.

These results indicate that the availability of foods limits the population size of these gulls. Recent trends in population size and the distrubution of the two gulls in Iceland lend additional support to this conclusion. There are indications that a divergence in size of the two species has occurred in Iceland.