| Summary: | The association between avian predation on Southern Rockhopper Penguins (Eudyptes chrysocome chrysocome) and subcolony size was examined during the chick-rearing period. In addition, activities of various predator and scavenger species at these subcolonies was documented and quantified for the first time. Subcolonies ranging from 69 to 1520 nests were observed for 461 and 386 hr, respectively, during December 2003 and 2004. Striated Caracaras (Phalocoboenus australis) were the most common predator/scavenger in all subcolonies except for two in which Kelp Gulls (Larus dominicanus) and Dolphin Gulls (Larus scoresbii) were dominant. The greatest numbers of predation and attempted predation events were observed on the functional and geometric edge of the subcolony. Kelp Gulls were only observed approaching central nests from the air. Striated Caracaras were mostly observed approaching nests on the geometric and functional edge from peripheral and central tussocks, respectively. In both years nest success was correlated with subcolony size. Small subcolonies in which predation was observed had a proportionally higher predation rate (predation rate per nest) than larger subcolonies with similar absolute predation rates, suggesting that if predation does occur, subcolonies may lower their predation risk by a dilution effect, once they have reached some minimum size. Subcolonies can also have zero or low predation risk when surrounded by larger subcolonies or when part of the territory of a Striated Caracara. Within each subcolony, nests in central locations of large subcolonies or those on the geometric edge of embankments seem to be the most protected from predation.
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