Population status and diet of the Yellow-legged Gull in the Azores.

Abstract

During 2004 a census of the Yellow-legged Gull (Larus michahellis atlantis) was conducted in the Azores to assess its present status in the archipelago. The census yielded an estimate of 4249 breeding pairs, an increase by almost 60% since the previous survey conducted in 1984. Gulls were detected on a total of 14 islets and/or sea stacks and are probably limiting the distribution of terns in the archipelago. Out of 37 gull breeding sites found during the 1984 and 2004 surveys, 24 were located within 1 km of tern colonies. All the gull colonies were coastal except Lagoa do Fogo on São Miguel Island. Pellet analysis indicated that gulls from all the colonies feed on refuse, but the percentage of pellets containing refuse on islands with small human populations was less than half than that of islands with more than 55000 inhabitants. Gulls have no direct competitors in the Azores and benefit from an increase in refuse production. The growing number and size of rubbish dumps over the last two decades has probably contributed to the large increase in the Azorean population.