ALBERT

Description: The foraging location, diving behavior, dietary composition, and feeding rates of female Emperor Penguins (Aptenodytes forsteri) from the Auster and Taylor Glacier colonies in Antarctica were investigated during the 1993 austral winter. The study was conducted between late May and early August, when male emperors remain at the colonies to incubate eggs and females forage at sea for self-maintenance. During winter, two satellite-tracked penguins from Auster foraged ≈100 km northeast of the colony in open water 200–500 m deep, over the outer continental shelf and shelf slope. Ten Auster and four Taylor Glacier penguins that carried time–depth recorders took ≈8 d to reach the ice edge, spent 50–60 d at sea foraging, and took 4 d to return across the fast ice to the colony. The females occasionally huddled together to minimize heat loss while in transit to the ice edge and between foraging days. The penguins foraged on 93.2% of their days at sea and rested for the remainder. On each foraging day, penguins usually entered the water just after dawn and averaged 4.71 h in the water before exiting at dusk. The hourly dive rate was constant throughout winter, but the daily dive rate increased as day length increased, suggesting that day length is a primary determinant of hunting effort. Penguins exhibited behavior indicative of foraging on 47% of their dives, the remainder being travel or search dives. Penguins made, on average, 26 foraging dives/d. Females from Auster targeted prey at water depths of 20–70 m and 100–150 m, whereas Taylor Glacier birds targeted prey at 10–70 m, 250–300 m, and 330–400 m, suggesting between-colony differences in prey distribution. The stomach contents of 17 females returning to Auster to brood their chicks were dominated by pelagic prey species: Antarctic krill (Euphausia superba, 70% by mass) and Antarctic silverfish (Pleuragramma antarcticum, 13% by mass). Food consumption rates during winter for five penguins from both colonies were similar and averaged 62.6 ± 5.8 g·kg−1·d−1 (1.8 ± 0.1 kg/d for a 28.8 kg female), which equated to a metabolizable energy intake of 236.6 ± 22.0 kJ/kg for each day they foraged (all values are mean ± 1 sd). This enabled the birds to gain ≈6.1 kg for a trip spanning ≈70 d. Based on mean prey masses and the penguins' dive rates, the penguins consumed ≈115 × 0.6 g krill or 16 × 4.3 g Antarctic silverfish per foraging dive, or some combination of both. In their winter trip, each breeding female consumed ≈100 kg of prey. The female populations at Auster and Taylor Glacier consumed an estimated 1350 Mg and 250 Mg of prey, respectively, in winter.

Description: We investigated the foraging location, diving behaviour, dietary composition, feeding rates and foraging trip durations of emperor penguins Aptenodytes forsteri raising chicks at the Auster and Taylor Glacier colonies on the Mawson Coast of Antarctica in the winter, spring and early summer of 1993, to examine seasonal changes in the penguins' foraging 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 penguins' 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 targeted prey in the vicinity of the continental slope mainly at depths 〈100 m, although some individuals frequently hunted at depths 〉200 m, and the 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 Antarctic krill to the diet reduced over time from 68% in August to 1% in early December. In November, the glacier squid Psychroteuthis glacialis dominated the diet (47 to 63%), and in early December the diet comprised 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 consumption 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 values are equivalent to metabolisable energy intakes of 628 ± 134 and 1422 ± 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 similar and declined from 15-19 d in spring to 〈10 d in early summer. Between hatching and about 1 wk prior to fledging each parent fed its chick 7 or 8 times. To raise a chick, females and males consumed approximately 410 and 470 kg of prey respectively, or 880 kg for each breeding pair. Seasonal variations in the penguins' foraging were probably influenced by fluctuating sea-ice conditions, differences in the prey types available, changes in day-length toward summer, and increasing demands of the growing chicks.