Geographical variation in the foraging behaviour of the pantropical red-footed booby
Résumé
While interspecific differences in foraging behaviour have attracted much attention,
less is known about how foraging behaviour differs between populations of the same species.
Here we compared the foraging strategy of a pantropical seabird, the red-footed booby Sula sula,
in 5 populations breeding in contrasted environmental conditions. The foraging strategy strongly
differed between sites, from strictly diurnal short trips in Europa Island (Mozambique channel) to
long trips including up to 5 nights at sea in Genovesa Island (Galapagos archipelago). The Expectation
Maximisation binary Clustering (EMbC) algorithm was used to determine the different
behaviours of individuals during their foraging trips (travelling, intensive foraging, resting and
relocating). During the day, the activity budget was similar for all the breeding colonies. During
the night, birds were primarily on the water, drifting with currents. At all sites, birds similarly performed
intensive foraging in zones of area-restricted search (ARS), although the size and duration
of ARS zones differed markedly. Red-footed boobies foraged over deep oceanic waters, with
chlorophyll a concentrations varying between sites. Birds did not appear to target areas with
higher productivity. We suggest that range differences between populations may be linked to
other factors such as intra- and interspecific competition.
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