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). Meas urements were made during three nesting stages: late incubation, the g uard stage (when small chicks were continuously guarded by at least on e parent), and the subsequent creche stage (when large chicks were lef t unattended). Nest relief cycle times decreased from 229 h during inc ubation to 33.3 h during the creche stage, and the fraction of time bi rds spent swimming increased from 20.8% during incubation to 31.6% dur ing the creche stage. The fraction of swim time spent in hunting dives and bottom time did not change significantly at different nesting sta ges. 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 di ffer 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 2 3.3% (creche stage) of the food metabolized by adults. Our data sugges t that (1) prey capture by Adelies is limited primarily by their abili ty to find krill swarms and not by limitations in harvest rates or ene rgy efficiency after prey have been located, and (2) reproductive effo rt in Adelies does not require a large increase in either energy expen ditures or foraging time.