Variability in foraging behaviour of chick-rearing macaroni penguins Eudyptes chrysolophus and its relation to diet

Flexibility in foraging behaviour and diet are characteristics of many penguin species. While these 2 aspects of foraging ecology are presumably tightly coupled, the connection between them is rarely examined directly. Using time-depth recorders and satellite telemetry we documented the foraging behaviour of 43 chick-rearing macaroni penguins Eudyptes chrysolophus at Heard Island. We also compared these behavioural data with prey recovered from the stomach contents of each tracked bird. During guard stage, foraging trips were significantly shorter (average duration = 23 ± 18 h, range = 47 ± 40 km) compared to crèche stage (average duration = 115 ± 112 h, range = 169 ± 102 km). Crèche stage trips also included significantly more shallow dives that appear to be related to travel (39% of dives <10 m versus 27% for guard stage). Three species dominate the birds' diet: 2 species of euphausiids and the myctophid fish Krefftichthys anderssoni. Over the breeding season, K. anderssoni was taken on trips further from the island with deeper dives compared to the euphausiids. Foraging characteristics also differed between trips targeting different euphausiid prey species; however, there was a temporal shift in the euphausiid species consumed and this was correlated with overall changes in foraging behaviour. Multivariate analysis of behavioural data from trips early in guard stage revealed 2 distinct foraging strategies: deeper and offshore versus shallower and inshore. Individual birds often switched between these strategies in successive trips. The characteristics of many dives performed during inshore trips were indicative of benthic foraging; a previously unrecorded behaviour for macaroni penguins. Euphausiids were captured on both offshore pelagic and inshore benthic trips, illustrating that when prey is found in different habitats substantial changes in foraging parameters can occur independent of dietary shifts. More detailed behavioural studies may allow prey-specific rather than habitat-specific foraging patterns to be distinguished. © Inter-Research 2008.