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, which 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, presence of helpers, and interactions with neighboring conspecifics. We investigated how these factors affect nest-site selection and nest survival in Acrocephalus sechellensis (Seychelles Warbler), a facultative cooperative-breeding passerine that defends stable territories year-round. We found that daily nest survival increased by ~1% for each meter higher in the canopy that a nest was placed. Nests were more likely to be located in food-rich parts of the territory, especially in territories with low overall densities of arthropods. Further, we found that nests in territories with helpers, which reduce nest predation in A. sechellensis, 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 build their nests 0.5 m closer to the border for each year the nearest neighboring male was older than their partner. Our results suggest that nest-site selection in A. sechellensis is affected by nest predation, food availability, helper presence, 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.