Foraging effort in Magellanic penguins in coastal Patagonia, Argentina

In long-lived species such as seabirds, foraging success is considered to be related to breeding success, so quantification of foraging parameters during the breeding season should help understand population trends. Using GPS units, we studied the foraging effort of 55 breeding Magellanic penguins Spheniscus magellanicus from 5 colonies in coastal Patagonia, Argentina (42 to 54 degrees S): Punta Norte, Bahia Bustamante, Puerto Deseado, Puerto San Julian and Isla Martillo, in an attempt to relate this to differences in breeding population trends. Measures of foraging effort-trip duration, total distance covered and maximun distance of the foraging trips from the breeding colony-decreased with increasing rate of population change. This information suggests that there are large differences in foraging effort and success among Patagonian penguin colonies, and penguins from Bahia Bustamante and Puerto Deseado, which are in the centre of the geographic range, require the highest foraging effort but are the least successful. It is plausible that lower population growth rates in these 2 colonies stem from the differences in food availability rather than any other process on land.