The diving behaviour of brooding king penguins (Aptenodytes patagonicus) from the Falkland Islands:: variation in dive profiles and synchronous underwater swimming provide new insights into their foraging strategies

The diving behaviour of king penguins (Aptenodytes patagonicus) was studied on the Falkland Islands, where a small population (ca. 300 fledglings year(-1)) is located at the geographical limit of their breeding range. King penguins rearing newly hatched chicks were equipped with time-depth recorders before leaving for sea. In total, 20,175 dives > 3 am were recorded from 12 birds during 15 foraging trips with a mean duration of 5.7 +/- 2.3 days. The majority of the trips was directed up to 500 km to the northeast of the breeding colony in slope waters of, and oceanic waters beyond, the Patagonian shelf. Mean time spent underwater accounted for 42 +/- 9% of the foraging trip. Mean dive depth achieved was 55 +/- 16 m; maximum dive depth recorded was 343 m. Mean dive duration was 159 +/- 25 s; maximum dive duration was 480 s. The mean vertical distance covered was 140 +/- 65 km trip(-1); and on average birds covered 25 km day(-1). Synchronous diving behaviour was observed in two birds for a period of about 24 h after leaving the colony. Dive depth correlated positively with: (1) light intensity, (2) dive duration and (3) vertical velocities, thus confirming previous findings obtained from conspecifics at other breeding sites and indicating comparable diving behaviour. However, separation of dives according to their profile - V-, U-, or W-shaped-revealed significant differences between certain dive parameters. For a given depth range, bottom time was longer and vertical velocities higher in W-dives than in U-dives. This, together with a higher number of W-dives at dawn and dusk, suggests that foraging is more effective during W-dives than U-dives, and during twilight. These findings imply that king penguins have to make more complex decisions, individually and socially, on the performance of the subsequent dive than previously thought.