DIVING BEHAVIOR OF EMPEROR PENGUINS NURTURING CHICKS AT COULMAN ISLAND, ANTARCTICA

At the largest known Emperor Penguin colony, we determined general fea tures of Emperor Penguin foraging commutes. The time selected for the study was one month before hedging, when maximum growth of the chicks occurs. Time/depth recorders were attached and retrieved from Eve adul ts as they departed from and returned to the colony. Nearly 16,000 div es were logged, of which 7,562 were estimated to be for foraging. Dura tion of the commutes averaged 14.9 days during which the birds average d a total of 3,188 dives or 213 dives per day. Dives <200 m occurred a t any time through the 24 hr cycle, and dives >400 m were restricted t o 05:00 to 19:00 hr. The deepest dive was 534 m and the longest was 15 .8 min to a depth <50 m. The modal depth of foraging dives was between 21 to 40 m, and the modal duration was between 4 and 5 min. Descent a nd ascent depth change rates were influenced by the maximum depth of t he dive, but usually for dives >100 m the rates fell between 1.0 to 2. 0 m sec(-1). The rates never exceeded 2.5 m sec(-1). Bottom time fract ion was 0.22 to 0.28 of total dive time, for dives >100 m. Although fe w in number, occurrence of dives >450 m appeared consistently during t he commute of every bird and suggests some important but unknown funct ion. Because dives >400 m occurred only during high sun periods, it is proposed that such dives may not occur during the austral winter nigh t. From behavioral data it appears that the aerobic dive limit (ADL) o f about 8 min is nearly twice the calculated ADL. If this is so, then <5% of all dives exceed the ADL. Diving efficiency derived from diving and surface time in relation to bottom time declines by 50% between 1 00 m and 300 m dives.