Sex-mediated changes in foraging behaviour according to breeding stage in a monomorphic seabird adapted to rural habitats

In contrast to sexually size-dimorphic species, monomorphic ones rarely show sexual differences in foraging behaviour as such variations have been primarily attributed to dissimilar body size. To investigate this aspect, we analysed foraging behaviour in breeding gull-billed terns, Gelochelidon nilotica, a monomorphic seabird adapted to rural habitats. We equipped 19 breeding birds with GPS devices and assessed differences in foraging behaviour and habitat use according to sex and breeding stage. Foraging trip distance and duration and daily frequencies were influenced by both breeding stage and sex, with females, but not males, performing closer, more frequent and shorter duration trips during chick rearing than incubation. Females, but not males, increased the repeatability of foraging metrics from incubation to chick rearing, while both sexes increased individual foraging site fidelity between the two breeding stages. Agricultural fields were the most exploited habitat for both sexes, but females made more use of aquatic habitats than males, especially during chick rearing. By foraging in different ways and in different habitats, the breeding pair can provide a wider range of prey types to their offspring, maximizing the chances of delivering high quantity and quality of food items under different environmental conditions. Our work provides new additional evidence of sex differences in foraging behaviour of monomorphic species, while highlighting the need to better understand underlying mechanisms driving foraging niche divergence and the consequences for fitness.