Divorce is widespread, not only in humans, but also in socially monogamous birds like the blue tit. Behavioural ecologists Mihai Valcu and Bart Kempenaers from the Max Planck Institute for Ornithology in Seewiesen found divorce rates of up to 50% in a long-term study of this species. But why do partners split up? To answer this question, it helps to know who suffers and who benefits from the separation.
Previous studies on small passerine birds, such as blue tits, have shown that females do better after divorce. This is because they had more offspring with a new partner. “These findings have led to the suggestion that the females should take the initiative to leave their partner”, says Bart Kempenaers, Director of the Department Behavioural Ecology and Evolutionary Genetics at the Max Planck Institute for Ornithology in Seewiesen.
In their study however, Kempenaers and his colleague Mihai Valcu obtained evidence that the increased reproductive success of divorced females may not be caused by getting a better partner, but by leaving the previous home and moving to a better place. Such breeding dispersal is common in females, in contrast to males, who rarely leave their territory after a divorce.
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