DIVING BEHAVIOR DURING FORAGING IN BREEDING ADELIE PENGUINS

We used electronic time depth recorders to examine diving patterns of Adelie Penguins (Pygoscelis adeliae) breeding near Palmer Station, Ant arctica. Most hunting dives consisted of a rapid descent to depth, a p eriod of bottom time at near-constant depth, and a rapid ascent to the surface. Most hunting activity occurred in bouts of consecutive dives to similar depths. Adelies foraged at depths between 3 and 98 m, with a mean of 26 m. Descent and ascent rates averaged 1.2 and 1.1 m/s, re spectively. Foraging was primarily diurnal, but there was relatively l ittle circadian change in foraging depth. The birds' overall hunting e ffort (cumulative bottom time) was concentrated between 0500 and 2 100 at depths between 10 and 40 m. Bottom time decreased slightly with in creasing depth but the correlation was weak. Dive duration was positiv ely correlated with dive depth. Maximum dive duration was 160 s; most hunting dives lasted 60-90 s with a mean of 73 s. Post-dive surface in tervals averaged almost-equal-to 50% of dive duration. Time use effici ency during dive bouts (bottom time/[dive duration + surface interval] ) decreased with increasing dive depth. Estimates of oxygen stores and diving metabolic rates indicate that the aerobic dive limit of Adelie s is 46-68 s and that most hunting dives require some anaerobic metabo lism. Use of anaerobiosis engenders an energy penalty and probably aff ects both the behavior and energetics of foraging.