Causes and consequences of divorce in a long-lived socially monogamous bird.

In socially monogamous species, sexual selection not only depends on initial mate choice but also mate switching. To date, studies lack assessment of (1) differences between passive (widowhood) and active (divorce) mate switching, (2) longer term fitness consequences (beyond the season post-divorce) and (3) how age masks reproductive costs and benefits of divorce. We investigated causes and short- and long-term consequences of mate switching and their age dependence using longitudinal data on Seychelles warblers (Acrocephalus sechellensis). Young and old males, but not females, divorced most frequently. Divorce propensity declined with pair-bond duration and reproductive success in both sexes, but mate switching did not incur short-term costs. Divorcees did not gain short- or long-term fitness benefits compared to non-divorcees. Rather, female early-life divorcees that lost their breeding position had lower survival than females that never divorced. Divorce is likely a strategy to escape poor-quality partnerships, but not all divorcees benefit from divorcing.