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 (Aptenody tes patagonicus) was studied at Heard Island (53 degrees 05'S, 73 degrees 3 0'E) during 1992/1993. On seven occasions throughout the breeding cycle, ti me-depth-light recorders were deployed on breeding adults to record the div e activities and foraging. Foraging locations changed with season: in autum n 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) al ong the northern ice limit, and 1220 km south of Heard Island to approximat ely 65 degrees S, respectively. In spring (October), the penguins again for aged further north than during winter. The foraging area utilised in Octobe r overlapped the area where the penguins foraged in March/April. The pengui ns' 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 di ve depths increased from 70 +/- 52 m in March 1992 to 160 +/- 68 m in Augus t 1992. Penguins dived deep (>50 m) only during daylight hours (16 h in Feb ruary, 9 h in July). Mean dive durations ranged from 2.9 +/- 1.1 min in Mar ch 1992 to 5.1 +/- 1.2 min in August 1992. Associated with changes in forag ing location and dive behaviour was a change in diet composition: during su mmer the penguins ingested mainly myctophid fish (>90%) while in winter the most important diet item was squid.