Y. Watanuki et al., DIVING PERFORMANCE OF ADELIE PENGUINS IN RELATION TO FOOD AVAILABILITY IN FAST SEA-ICE AREAS - COMPARISON BETWEEN YEARS, Journal of Animal Ecology, 62(4), 1993, pp. 634-646
1. Between-year variation in adelie penguin Pygoscelis adeliae foragin
g behaviour was studied using time-depth recorders at a colony in Lutz
ow-Holm Bay, Antarctica 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 availabili
ty was poor in 1991 when compared to 1990. However, mass of food broug
ht to chicks per shore visit and rate of decrease of parental mass did
not differ between these years. 2. In 1991, the penguins on average d
ived 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 durat
ion). However, time under water, the number of dive bouts per day and
dive bout duration did not differ significantly between 1990 and 1991.
3. Foraging trip duration of birds carrying the time-depth recorders
in mid to late January was longer in 1991 (861 +/- 419 min) than in 19
90 (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 19
91. These indicate that probability of locating a prey patch was lower
in 1991 than in 1990, but once a prey patch was found total diving ef
fort was similar to that in 1990. 4. These data show that when food wa
s less abundant adelie penguin parents increased the duration of their
foraging trips, thereby decreasing meal delivery rate, but did not in
crease total diving effort to compensate for poor food availability. T
he reasons for this might be that (i) their foraging sites were highly
restricted to small ice holes or tide cracks; therefore, prey abundan
ce within sites might decrease rapidly by depletion and the penguins m
ight not be able to get more food even if they forage for a longer per
iod; or (ii) they have a priority to maintain their body condition for
their own future survival at the expense of offspring production.