Search behavior of a small-range marine predator: the Imperial Cormorant

S HARRIS; A RAYA REY; F QUINTANA

Victoria, Canada

Conferencia; 1st World Seabird Conference; 2010

Predators must make optimal decisions about where and how to forage in order to maximize both their efficiency and, ultimately, their fitness. Our main objective is to characterize the search strategy of Imperial Cormorants (Phalacrocorax atriceps) breeding at Punta León colony (43° 04´ 40´´S, 64° 29´45´´W) Chubut, Argentina. Specifically, to determine if birds perform Area-Restricted Search (ARS) through the use of first-passage time analysis (fpt). Consequently, to study if the detected search scales are nested, if initiation of this behaviour is triggered by prey detection and pursuit, and characterize ARS areas. GPS information was gathered from 26 foraging trips (11 males and 15 females), during 2008 breeding season. In 88% of the trips at least one search scale was detected (range = 25.25 - 4343.43m), in some cases more than one and even nested scales were found. Individuals used as many as three ARS areas (average size = 2.4km) throughout the trajectory, spending on average 35% of total time within them. ARS was performed in shallow waters, with a mean bathymetry of 29 ± 14 m (range: 5-57 m). In 48% of the trips the highest proportion of dives occurred within the ARS and all but one trip presented dives within the 10 minutes prior to entering an ARS. We conclude that Imperial Cormorants that breed at this colony perform ARS, some individuals present a nested search strategy and prey detection may trigger ARS. However, behavioral differences were found which could be related to individual specialization or age/experience related divergences.