Nest-site selection and nest predation in a tropical passerine in relation to food, friends and foes

Nest-site selection is an important determinant of avian reproductive success, mainly through its effect on predation risk. However, how environmental and social factors affect nest-site selection and predation risk remains less well understood. Optimal nest positioning may depend on the balance of many distinct factors such as nest predation, food availability, extra-pair mating opportunities, and interactions with neighbouring conspecifics. We investigated how these factors may affect nest-site selection and nest survival in the Seychelles warbler (Acrocephalus sechellensis), a facultatively cooperative-breeding passerine that defends stable territories year-round. We found that nest survival was higher when nests were built in higher vegetation layers and that nests were more likely to be located in food-rich parts of the territory, especially in territories with lower food availability. Further, we found that nests in territories with helpers were built in areas with higher food availability, whereas nests in territories without helpers were built in areas with fewer nest-predators. Finally, we found that females paired with younger males tended to build their nest closer to the territory border. Our results suggest that nest-site selection in the Seychelles warbler is affected by nest-predation, food availability and, possibly, the female’s opportunity for extra-pair copulations. Clarifying the relative importance of these different selective factors is key to the understanding of optimal nest-site selection to maximize reproductive success.