Flexible foraging patterns under different time constraints in tropical boobies

Abstract

The foraging behaviour of any animal is intricately linked to ecological constraints. Extrinsic factors, such as daylength, may limit the time available for foraging. Intrinsic factors, such as the coordination of mates at a nest site, may exacerbate this limitation. Using activity loggers, we examined the effects of extrinsic and intrinsic limitations on the foraging behaviour of the sympatric red-footed booby, Sula sula, and brown booby, Sula leucogaster, during incubation, and tested the prediction that individuals would work harder when time available for foraging was limiting. Both species share incubation duties and forage by day. Brown boobies made significantly shorter foraging trips than red-footed boobies, and thus, both parents could forage during the same day. Therefore, departure time and time available for foraging will also be influenced by when the partner returns to the colony. Overall foraging trip duration decreased linearly with respect to departure time. Our study suggests that the time available for foraging is limited by a combination of extrinsic and intrinsic processes in both species. Crucially, the rate of flying and diving, indicators of prey search and pursuit, respectively, increased with decreasing time available for foraging, whereas time spent inactive on the sea surface decreased, as did the time between departure and diving. Our data therefore suggest that boobies adjust their foraging behaviour according to extrinsic constraints.