Gull Predation on Leach’s Hydrobates leucorhous and European Storm-petrels H. pelagicus on Elliðaey Island, Iceland

Abstract

Studies of predator-prey interactions, and quantification of predation frequencies can be crucial to understanding prey population declines. We present a study of gull Larus spp. predation on Leach’s Storm-petrels Hydrobates leucorhous and European Storm petrels H. pelagicus, relative to other prey types. We studied a population of approximately 160 gulls in mixed colonies of Herring Gulls L. argentatus and Lesser Blackbacked Gulls L. fuscus, on Elliðaey Island, Iceland. We dissected 191 pellets and found gulls fed mostly on avian prey, insects and molluscs. We estimate that the total consumption of Leach’s Storm-petrels by all gulls in the colonies amounted to approximately two individuals per day, over the course of the study. European Stormpetrels were not preyed upon in high quantity during the study period, with a minimum of one individual depredated within a four-day study period, potentially reflecting the later breeding season of this species. We also provide a correction factor of pellets produced per storm-petrel consumed, which could be used to quantify the number of individual storm-petrels consumed from counts of pellets in future studies.