Seasonal change in foraging areas and dive depths of breeding king penguins at Heard Island

The seasonal variation in the foraging behaviour of king penguins (Aptenodytes patagonicus) was studied at Heard Island (53 degrees 05'S, 73 degrees 30'E) during 1992/1993. 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 degrees S and 74-78 degrees 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 degrees E) along the northern ice limit, and 1220 km south of Heard Island to approximately 65 degrees S, respectively. In spring (October), the penguins again foraged further north than during winter. The foraging area utilised in October overlapped the area where the penguins foraged in March/April. The penguins' diving behaviour also varied seasonally: the 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 m in March 1992 to 160 +/- 68 m in August 1992. Penguins dived deep (>50 m) only during daylight 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 was a change in diet composition: during summer the penguins ingested mainly myctophid fish (>90%) while in winter the most important diet item was squid.