ENERGETICS OF FORAGING IN BREEDING ADELIE PENGUINS

We studied foraging energetics in Adelie Penguins (Pygoscelis adeliae) using doubly labeled water (DLW) and time-depth recorders (TDR). Measurements were made during three nesting stages: late incubation, the guard stage (when small chicks were continuously guarded by at least one parent), and the subsequent creche stage (when large chicks were left unattended). Nest relief cycle times decreased from 229 h during incubation to 33.3 h during the creche stage, and the fraction of time birds spent swimming increased from 20.8% during incubation to 31.6% during the creche stage. The fraction of swim time spent in hunting dives and bottom time did not change significantly at different nesting stages. Field metabolic rates (FMR) were 2.73 x basal metabolic rate (BMR) during incubation, 3.03 x BMR during the guard stage, and 3.29 x BMR during the creche stage; due to high variance these values did not differ significantly. Estimated metabolic rate during swimming was 8.2 x BMR. Rates of prey capture (grams of krill per hour of swimming, per hour of hunting dives, and per hour of bottom time) did not change at different stages. Food provided to chicks was 20.9% (guard stage) to 23.3% (creche stage) of the food metabolized by adults. Our data suggest that (1) prey capture by Adelies is limited primarily by their ability to find krill swarms and not by limitations in harvest rates or energy efficiency after prey have been located, and (2) reproductive effort in Adelies does not require a large increase in either energy expenditures or foraging time.