Animal Behaviour 67: 985-992 (2004)
A fine-scale time budget of cape gannets provides insights into the foraging strategies of coastal seabirds
Ropert-Coudert Y, Gremillet D, Kato A, Ryan PG, Naito Y, Le Maho Y
Central-place foragers organize their feeding trips to ensure their own body maintenance, and provide their offspring with food. In seabirds, several long-range foragers have been shown to alternate long and short trips to balance these dual needs. However, the strategies of short-range foragers remain poorly understood. To address this question, we examined the time budget of breeding cape gannets (Morus capensis) foraging off the coast of South Africa using a precise, miniaturized motion sensor. Birds stayed at sea from 5.5 to 25.3 hours, occasionally spending the night at sea. The large number of isolated dives and extended flight time observed during these overnight trips suggested that birds either experienced poor foraging conditions or exploited more distant, yet more profitable prey patches. Conversely, birds which stayed at sea for less than 1 day had relatively consistent activity patterns . Most of these birds (88%) foraged actively at the beginning and the end of the foraging trip. These feeding bouts were separated by protracted periods of sitting at the sea surface. Such resting periods probably serve to digest the food ingested during the first part of the foraging trip, allowing birds to feed initially for themselves, and then to provision for their chick on the way back to the breeding site.
BD04-02
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