CONICET | Buscador de Institutos y Recursos Humanos

In rockhopper penguins Eudyptes chrysocome, the relationship between foraging effortand the daylight period is unclear. We studied the foraging ecology of female southern rockhoppersthat were brooding chicks at Bahía Franklin (Staten Island) in December 2000. We compare our datawith data presented for other subspecies and locations, analyzing the features of their foraging ecologyand its relationship with the daylight period around Staten Island, the population size of differentbreeding locations and the marine environment. Southern rockhopper penguins performedlonger trips (about 30 and 60% longer for daily and overnight trips respectively) and between 5 and7 more overnight trips (53%) than the northern and eastern subspecies. Mean dive depth and diveduration were 28.9 ± 24.6 m and 79 ± 30 s respectively. The diving rate (30.4 ± 5.0 dives h1), and theproportion of trip duration underwater (66.2 ± 5.9%) confirmed the high foraging effort of rockhopperpenguins. During the study period foraging trip duration increased, but dive parameters did notvary. Penguins traveled as much as 20 km to their foraging waters, either in shelf waters and/or inwaters of a close shelf-break and slope. The diet was dominated in numbers by euphausiids,amphipods, cephalopods, fish larvae and juveniles, all prey species commonly found in Subantarcticwaters. The long trips could be explained by the long twilight period and by diel vertical migration ofprey, confirming the phenotypic plasticity of penguins in response to different marine environments.The extended foraging trip duration may contribute to sustaining the high level of the breedingpopulation (167 000 breeding pairs) at Bahía Franklin, and account for differences in the recent historyof different breeding colonies in the SW Atlantic Ocean.

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