Stealing food from conspecifics: spatial behavior of kleptoparasitic Common Terns Sterna hirundo within the colony site

GARCÍA GERMÁN OSCAR; RIECHERT JULIANE; FAVERO MARCO; BECKER PETER H

Conferencia; Conference of the Waterbird Society and the International Wader Study Group; 2013

Parasitic interactions over food are one of the most widespread forms of exploitation within and among species and there is a vast body of literature describing the many forms of such behavior (e.g. kleptoparasitism). Kleptoparasitism is a form of competition that involves stealing food already procured by another forager, and is one of the most common types of exploitation in seabirds. Here, we analyzed the spatial movements of individuals transponder-marked Common Terns (Sterna hirundo) within the colony site during the chick rearing period, supplemented by foraging observations, in relation to the trophic strategy (namely kleptoparasitic vs. honest birds). Attendance pattern (time spent at colony site per day, number and location of resting platforms used) were compared between kleptoparasitic (n=11), and honest individuals (n=26). A total of 725 kleptoparasitic attacks were recorded during the chick rearing period. We found differences between genders in the tactic used to steal food and the area chosen to perform the attacks: females attacked in the vicinity of their nest, while males attacked further away. We found clear differences in the spatial pattern between both groups: kleptoparasites used more resting platforms and moved more widely across the colony site than honest individuals, and parasitic females were registered longer in the colony during the day than honest ones. Our results show a differential use of the colony site dependent on the foraging strategy. Parasitic birds use the colony as a foraging patch, exploring the colony looking for feeding opportunities (i.e. kleptoparasitic attacks). In contrast, honest individuals spend much time outside the colony foraging to feed their chicks.