R. Kirkwood et G. Robertson, SEASONAL CHANGE IN THE FORAGING ECOLOGY OF EMPEROR PENGUINS ON THE MAWSON COAST, ANTARCTICA, Marine ecology. Progress series, 156, 1997, pp. 205-223
We investigated the foraging location, diving behaviour, dietary compo
sition, feeding rates and foraging trip durations of emperor penguins
Aptenodytes forsteri raising chicks at the Auster and Taylor Glacier c
olonies on the Mawson Coast of Antarctica in the winter, spring and ea
rly summer of 1993, to examine seasonal changes in the penguins' forag
ing ecology. As day-length increased after winter, the penguins' daily
swimming time increased from 7.83 +/- 1.50 h in August to 12.23 +/- 1
.25 h in September and 12.95 +/- 1.24 h in October. Accordingly, the p
enguins' dive rate increased from 92.7 +/- 28.5 to 149.4 +/- 23.4 and
161.6 +/- 19.3 dives d(-1) in the respective months. The birds targete
d prey in the vicinity of the continental slope mainly at depths <100
m, although some individuals frequently hunted at depths >200 m, and t
he maximum depth achieved was 438 m. Antarctic krill Euphausia superba
were the most common prey taken overall, 41% of the diet by mass, and
dominated the diets between August and October. The contribution of A
ntarctic krill to the diet reduced over time from 68% in August to 1%
in early December. In November, the glacier squid Psychroteuthis glaci
alis dominated the diet (47 to 63%), and in early December the diet co
mprised various species of fish, Trematomus species (27%), Pagothenia
borchgrevinki (24%), and Pleuragramma antarcticum (8%), and squid, P.
glacialis (13%) and Alluroteuthis antarcticus (9%). The birds' prey co
nsumption rates more than doubled between late winter and early summer
, from 4.0 +/- 1.0 to 8.7 +/- 1.7 kg d(-1) spent foraging; these value
s are equivalent to metabolisable energy intakes of 628 +/- 134 and 14
22 +/- 308 kJ kg(-1) d(-1), respectively. During brooding (late winter
to early spring), females spent less time at sea than males (8.7 +/-
2.7 vs 17.7 +/- 3.8 d); thereafter trip durations of both sexes were s
imilar and declined from 15-19 d in spring to <10 d in early summer. B
etween hatching and about 1 wk prior to fledging each parent fed its c
hick 7 or 8 times. To raise a chick, females and males consumed approx
imately 410 and 470 kg of prey respectively, or 880 kg for each breedi
ng pair. Seasonal variations in the penguins' foraging were probably i
nfluenced by fluctuating sea-ice conditions, differences in the prey t
ypes available, changes in day-length toward summer, and increasing de
mands of the growing chicks.