Seasonal and interannual variation in foraging range and habitat of macaroni penguins at South Georgia

In marine ecosystems, characterisation of the foraging areas and habitats of predators is a key factor in interpreting their ecological role. We studied the foraging areas of macaroni penguins at Bird Island, South Georgia, throughout the breeding seasons of 1999-2001 using satellite tracking. We investigated differences in foraging ranges and characteristics between different stages of the breeding season, between sexes, between years and between individuals. During incubation, on foraging trips of 10-26 days, both sexes travelled long distances from Bird Island (male average = 572 km; female average = 376 km) in a north-westerly direction towards the Maurice Ewing bank; some individuals, particularly males, travelled across the Polar Front to forage in the Polar Frontal Zone. In contrast, during the chick-rearing period, both sexes mainly foraged relatively close (average 62 km) to South Georgia over the continental shelf. Foraging trip characteristics differed between males and females during chick rearing: females traveled further on average and on more direct trips. During chick rearing, males and females on longer foraging trips covered longer distances and travelled further from Bird Island. There were no interannual differences in characteristics of foraging trips although sex differences in some parameters varied between years. The bearings of chick-rearing foraging trips were non-random and most were in a north-westerly direction. Variation, both intra- and inter-individual, in bearings of foraging trips was high. Travel speeds were slower during foraging trips in the chick-rearing period than during incubation, probably relating to the differences in distances travelled. The stage of the breeding season, the constraints on the penguins during different stages, and sex were important in determining variation in foraging range and characteristics in macaroni penguins, but year and individual effects were relatively unimportant.