Foraging strategy of King Penguins (Aptenodytes patagonicus) during summer at the Crozet Islands

The foraging ecology of King Penguins (Aptenodytes paragonicus) at Possession Island, Crozet Archipelago, was studied between January and March 1993 and between February and March 1994. Diving activity and position of the birds were determined via externally attached logging units. Feeding behavior was detected using stomach temperature sensors. All calculated positions of the birds occurred south of Possession Island. The area most frequented was situated 250 km south of the island (48.5 degrees S), where birds stayed for 40 h during a foraging trip, on average. The overall swim speed differed with time into the foraging trip, being lowest during the central part and highest (10 km/h) during the last night at sea, when birds were returning to the colony. Diving activities showed a clear diurnal pattern, with maximum dive depth being dependent on ambient light levels. During the night, only shallow dives <30 m were made, whereas deep dives occurred only during daylight. Preferred dive depths during deep diving ranged from 100 to 200 m. Maximum dive depth was 323 m, and maximum dive duration was 9.2 min. Vertical velocity (rate of change of depth) and dive duration were significantly correlated with increasing dive depth. Time spent at depth changed with time into the foraging trip, with most time being spent in deep water strata during the central phase, whereas predominately shallow dives were executed at the beginning and at the end of the foraging trips. Feeding success was closely linked to time of day, dive depth, and time into the foraging trip. Overall, >85% of the feeding events occurred during daylight and at twilight. Mean food mass ingested was calculated to be similar to 2350 g/d, with the highest amounts ingested during the central and penultimate days of the foraging trip. Foraging success (grams ingested per unit time underwater) was also highest (>370 g/h) at this time. The relationships between foraging strategy, inter- and intraspecific competition, and King Penguin body mass are discussed.