Male but not female Kentish plovers Charadrius alexandrinus modulate foraging behaviour according to tide during incubation

During breeding, birds have to find a balance between reproductive tasks and the need to recover their energy. Foraging movements are constrained in time and space by brood guarding and chick-rearing activities at the nesting site. Foraging behaviour differs among species according to their ecology but it can change, even markedly, among individuals of the same species according to intrinsic and extrinsic factors, such as sex, habitat, intra and inter-specific interactions. By means of individual GPS tracking, we assessed foraging behaviour of egg-incubating Kentish plovers breeding along a sandy beach bordering the Venice Lagoon. Both sexes foraged on the beach were they bred, but also in the lagoon, travelling up to 16 km far from the nest. In both habitats, individuals foraged in areas that were significantly separated from those used by other tagged conspecifics, likely lowering intra-specific competition. Males foraged mainly at daytime, in the lagoon at low tide and on the beach at high tide. Differently, females foraged mainly at night and in the lagoon, and less often on the beach exclusively during daytime, regardless of tide height. The avoidance of nocturnal foraging on the beach by females might be explained as antipredatory response to the presence of owls breeding in a pinewood adjacent the beach or to a possible diet specialization on prey that are available in the lagoon at night, irrespective to tide conditions. Overall, this study revealed an unexpected sexual difference in foraging behaviour of Kentish plover, with sexes likely facing different environmental pressures according to diurnal and nocturnal foraging.