Free as a bird? Activity patterns of albatrosses during the nonbreeding period

This is the first comprehensive study of at-sea activity patterns of albatrosses during the nonbreeding period, based on data from combination geolocator immersion loggers deployed on the wandering albatross Diomedea exulans, black-browed albatross Thalassarche melanophris, grey-headed albatross T. chrysostoma and light-mantled albatross Phoebetria palpebrata from South Georgia (54 degrees 00' S, 38 degrees 03' W). Differences in behaviour among species observed during the breeding season were maintained during the nonbreeding period, suggesting a high degree of foraging niche specialisation. Wandering albatrosses exhibited longer flight bouts, and spent more time on the water during daylight, than any of the smaller species. Light-mantled albatrosses were the most active nocturnally. During daylight, grey-headed albatrosses were the most aerial and black-browed albatrosses had the shortest flight bouts. Although all species still engaged in foraging behaviour predominantly during daylight, they spent a greater proportion of time on the water (presumably resting) during the nonbreeding period compared with the breeding period, suggesting that they could more readily meet their energy demands when no longer subject to central place constraints. There was no evidence from activity patterns that might suggest that wing feather moult handicaps flight capability during the nonbreeding period. Individuals of all species engaged in rapid east west commutes, when considerably higher proportions of time were spent in flight than while resident, in particular during daylight, possibly because birds are unable to navigate effectively during complete darkness. Despite consistency in individual dispersal patterns, there were year-to-year differences in the nocturnal behaviour of black-browed albatrosses, probably attributable to prey variability.