Summary
The seasonal variation in the foraging behaviour of king penguins Aptenodytes patagonicus was studied at Heard Island (53°05S, 73°30E) during 1992/93. On seven occasions throughout the breeding cycle, time-depth-light recorders were deployed on breeding adults to record the dive activities and foraging. Foraging locations changed with season: in autumn and spring 1992, adults foraged between 48-52°S and 74-78°E, about 370 km NNE of Heard Island close to the Polar Front. Two penguins tracked in winter travelled 2220 km east of Heard Island (95°E) along the northern ice-limit, and 1220 km south of Heard Island to approximately 65°S, respectively. In spring (October), the penguins foraged again further north than during winter. The foraging area utilised in October overlapped the area where the penguins foraged in April/March. The penguins diving behaviour also varied seasonally: modal depth of deep dives (> 50 m) increased from about 100 m in February to 220 m in October. Mean dive depths increased from 70 ± 52 in March 1992 to 160 ± 68 in August 1992. Penguins dived deep (> 50 m) only during day light hours (16 h in February, 9 h in July). Mean dive durations ranged from 2.9 ± 1.1 min in March 1992 to 5.1 ± 1.2 min in August 1992. Associated with changes in foraging location and dive behaviour is a change in diet composition: during summer the penguins ingested mainly myctophid fish (> 90 %) while in winter the most important diet item was squid.