Journal of Animal Ecology 1993,62,634-646
Diving perfection of adelie penguins in relation to food availability in fast sea-ice areas; comparison between years
Watanuki, Y., A. Kato, Y. Mori and Y. Naito 1993
Between-years variation in adelie penguin Pygoscelis adeliae foraging behaviour was studied using time-depth recorders at a colony in Lutzow-Holm Bay, Antartica in the summers of 1990 and 1991 in areas where fast sea-ice remained. Poor chick survival and growth, long foraging trip duration and low meal delivery rate indicate that food availability was poor in 1991 when compared to 1990. However, mass of food brought to chicks per shore visit and rate of decrease of parental mass did not differ between these years.
In 1991, the penguins on average dived deeper(12.3 ± 4.2 m) and for longer durations (1.9 ± 0.2 min) than they did in 1990 (7.1 ± 1.6 m depth and 1.5 ± 0.2 min duration). However, time under water, the number of dive bouts per day and dive bout duration did not differ significantly between 1990 and 1991.
Foraging trip duration of birds carrying the time-depth recordersin mid to late January was longer in 1991 (861 ± 419 min) than in1990 (502 ± 199 min) because travelling/searching time within trips in 1991 was about four times as long as it had been in 1990. Total dive bout duration within foraging trips did not differ between 1990 and 1991. These indicate that probability of locating a prey patch was similar to that in 1990.
These data show that when food was less abundant adelie penguin parents increased the duration of their foraging trips, thereby decreasing meals delivery rate, but did not increase total diving effort to compensate for poor food availability. The reason for this might be that (i) their foraging site were highly destricted to small ice holes or tide cracks; therefore, prey abundance within sites might decrease rapidly by depletion and the might not be able to get more food even if they forage for a long period; or (ii) they have a priority to maintain their body condition fot their own future survival at the expense of offspring produdction.
PG93-2
|
