Socio-ecological conditions and female infidelity in the Seychelles warbler

Within socially monogamous breeding systems, levels of extra-pair paternity can vary not only between species, populations and individuals, but also across time. Uncovering how different extrinsic conditions (ecological, demographic and social) influence this behavior will help shed light on the factors driving its evolution. Here, we simultaneously address multiple socio-ecological conditions potentially influencing female infidelity in a natural population of the cooperatively breeding Seychelles warbler, Acrocephalus sechellensis. Our contained study population has been monitored for over 25 years, enabling us to capture variation in socio-ecological conditions between individuals and across time and to accurately assign parentage. We test hypotheses predicting the influence of territory quality, breeding density and synchrony, group size and composition (number and sex of subordinates), and inbreeding avoidance on female infidelity. We find that a larger group size promotes the like...