The Auk 109(2);223-234,1992
Diving pattern and performance in non breeding gentoo penguins (Pygoscelis papua) during winter
Williams, T.D., A. Kato, J.P. Croxall, Y. Naito, D.R. Briggs, S. Rodwell and T.R. Barton 1992
We studied diving patterns and performance (dive depth, duration, frequency and organization during foraging trip) in relation to diet non breeding gentoo penguins (Pygoscelis papua) over 59 days (involving 5,469 fives ) in winter. We estimated foraging ranges and prey caputure rates, and compared foraging behavior with that of breeding (chick-rearing) birds. Foraging was highly diurnal with 98% of foraging trips completed during the same day. foraging-trip frequency was 0.8/day, trip duration was 6-8 h, and birds spent 51-62% of foraging trip diving. Dive depth and durtion were bimodal. Shallow dives (>21 m ; 42%of total number and 16% of total dive time) averaged 5-7 m and 0.5-1.3 min. Deep dives (>30 m 55% of total number and 81% of dive time) averaged 74-105 m and 2.7-3.5 min, respectively. Deep-dive duration exceeded the subsequent surface interval, but shallow dives were followed by surface intervals two to three times dive duration. Deep dives showed clear diel patterns, averaging 10-20 m at dawn and dusk 70-90 m at midday. These results are consistent with the patchy vertical and horizontal distribution and diel movements of Anterctic krill, the main winter prey of gentoo penguins (including study birds). We suggest that shallow dives are mainly serching dives, and deesp dives mainly for feeding. Foraging activity of non breeding gentoo penguins in winter is similar that of chick-rearing birds. The only major diffarences are that foraging-trip frequency is 20% less and stmach content mass on return ashore 30% less in winter. We conclude that of foraging activity in gentoo penguins is changed by varying frequency and duration of foraging trips, rather than by changing pattern and rate of diving.
PG92-1
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