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Geographical variation in the foraging behaviour of the pantropical red-footed booby

Abstract:

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.