Summary
To determine the foraging space of Emperor penguins Aptenodytes forsteri in winter 12 females from Auster colony (13 400 pairs) were equipped with satellite transmitters and time-depth recorders before departing on their 77 ± 8 d winter (June-August) foraging trip. The females were also injected with tritiated water (3H2O) to estimate food consumption, and non-instrumented females were stomach sampled upon return to the colony to determine their diet. The same data were collected in August/September from 3 males foraging after their 4-month pre-nuptial and incubation fast. Both females and males foraged in pack-ice within 120 km of the colony along a relatively narrow band of the continental shelf in water depths ranging from 200 to 500 m. Only rarely did penguins leave shelf waters to forage in deeper water over the shelf break. The size of the general foraging area for females was about 11 410 km2, but 50 % of all foraging days was spent in only about 15 % (1 700 km2) of the total foraging area. A female of average mass (25 kg) hunted for about 6 h d-1, and consumed 1.8 kg of food per foraging day. This indicates that females from Auster consumed in winter about 1 520 t, about half of which is likely to have been taken from an area measuring only 60 x 28 km. Males were active for about 10 h d-1 and consumed about twice as much (3.7 ± 1.2 kg d-1 for 24-kg male) as the females during the early phase of brooding. The diet of females comprised 72 % fish (by mass), 16 % squid and 12 % Antarctic krill Euphausia superba whereas that of the males comprised 53 % fish, 2 % squid and 43 % krill. Most foraging dives of females (81 %) and males (64 %) were to < 200 m and lasted less about 3 minutes. Males dived deep (> 300 m) more frequently than females (19.8 % versus 0.1 %) but the number of dives per day was similar for both sexes (27 ± 14 for winter females, 31 ± 15 for brood-stage males). The small foraging area, diet composition and