Impacts of intraspecific kleptoparasitism and diet shifts on Razorbill Alca torda productivity at the Gannet Islands, Labrador

Abstract

Intraspecific kleptoparasitism, the stealing of food from members of the same species, has received widespread but mostly superficial attention in the scientific literature. However, the effects of such behavior can be significant. Here we report on high rates of intraspecific kleptoparasitism in the Razorbill Alca torda at the Gannet Islands, a behavior that appears to be colony-specific. Razorbills carry their prey conspicuously in the bill, making them vulnerable to kleptoparasitic attacks from neighboring birds. We examined the relationship between the frequency of kleptoparasitic attacks and the prey species carried by breeding adults. During 2003-2006, 69% of all Razorbills carrying food to a chick were attacked (n = 182) and of these attacks, 18% (n = 22) were successful. Group attacks (two or more kleptoparasites) were more successful numerically (27%, n = 71), but only one member of the group ever received the reward. The frequency of kleptoparasitism observed by Razorbills at the Gannet Islands is one of the highest reported for any seabird, including many specialist kleptoparasites such as frigatebirds. This finding, combined with the lowest observed Razorbill productivity (overall success = 0.39, n = 222) for the Gannet Islands and drastic shifts in diet, may indicate decreased food availability.