DEPTH UTILIZATION BY BREEDING ADELIE PENGUINS, PYGOSCELIS-ADELIAE, AT ESPERANZA BAY, ANTARCTICA

Miniature depth gauges were attached in December 1987 and January 1988 to Adelie penguins, Pygoscelis adeliae, breeding at Esperanza on the Antarctic Peninsula. Results from 34 birds showed that foraging penguins with eggs and with brooded and creching chicks spent mean periods away from the nest of 96, 36 and 21 h, respectively, during which time means of 29.0 h (30%), 11.2 h (31%) and 2.7 h (13%), respectively, were spent under water at depths > 5 m. Time under water was positively correlated with time absent from nest. Maximum depth reached was 170 m but overall birds spent most time at shallower depths. Birds foraging for brooded chicks dived deeper than birds foraging for creching chicks. Stomach-pumping indicated that the principal prey caught at this time was krill, Euphausia superba. Mean mass changes of adults during single foraging trips indicated that krill were caught at a mean rate of 7.2 g min-1 spent under water.