Although the majority of bird species form a stable pair bond at least over some period of time, offspring are regularly fathered by another than the female’s social mate. Therefore, copulations outside of the pairbond, so called extra-pair copulations, must occur regularly and dawn seems to be a critical time for them. Indeed, a study on great tits (Parus major
) suggested that females that have extra-pair offspring emerge relatively early from their roosting place. In small, cavity-nesting passerines, the blue tits (Cyanistes
caeruleus), researchers from the Department of Behavioural Ecology and Evolutionary Genetics investigated whether early emerging blue tit females are indeed more successful in having extra-pair offspring. To do so, they combined a long-term dataset on natural female emergence times, and an experiment where the researchers exposed roosting females to additional light before sunrise thereby advancing their emergence time.