Foraging strategy of the Commander Islands glaucous-winged gull (Larus glaucescens) population [Russian]

摘要

The feeding bahavior of glaucous-winged gulls was observed on the Commander Islands during 1992-1993 and 1998-1999. Analysis of 5412 food samples makes it possible to reveal differences in the foraging strategy of breeding and nonbreeding gulls. The preferable food of nonbreeding gulls was the fly Fucomyia frigida larvae dwelling decaying brown algae. In 1993, their share was 99% of the total food. The foraging strategy of nonbreeding gulls was their permanent presence near a food source. They used seasonal food only at its high abundance. The number of gulls was directly proportional to the food abundance. Breeding gulls preferred the food from the neighboring animal farm (53.3%). The share of this food increased in the absence of natural forage. When the animal farm was closed, the number of gulls in the colony was reduced by two times, and the share of fish in the diet increased from 2.3 to 45.6%. The forage behavior of the gull population from the Commander Islands differ significantly from that in North American gulls attesting to the isolation of the insular population.