Surviving the winter: Pelagic behavior of Magellanic penguins

In this long-lived seabird, reproductive rates are low but adult survival is generally high. Adult mortality is thought to be mainly from starvation during the winter, when birds swim hundreds or thousands of kilometers. To better understand winter survival and habitat use, we created an energetic model of winter behavior, using satellite telemetry of birds in both Argentina and Chile during the austral fall and winter. To interpret their behavior from this location data, we first extracted statistical descriptions of different behaviors from telemetry of other birds during breeding season foraging trips. During breeding, the birds are central-place foragers, constrained to return to the colony to incubate eggs or feed chicks. Based on distance from colony, stereotypical trips to sea were divided into outbound, inbound, and foraging activities. Differences observed in travel speed and turning angle between satellite observations were hypothesized to result from different ratios of transit, resting, and foraging behavior during different activities. Inbound tracks showed the straightest path and highest travel speeds (transit). Outbound tracks had somewhat more turning and slower travel speeds (transit, resting). Foraging showed the least consistent directionality and lowest travel speeds (foraging, resting). We then used these statistical descriptions to assign behaviors to segments within the winter tracks, and assessed the energetic consequences. We also analyzed the degree to which foraging behavior occurs in areas of higher relative chlorophyll concentration, to assess whether chlorophyll is a useful proxy for prey availability. The model combines these data with geographical and life history constraints and marine habitat productivity to explore how birds respond to environmental variation when unconstrained by breeding activities. The model can also be used to predict possible responses to anthropogenic modification of the marine environment.