Social monogamy is a rare mating system among animals, occurring commonly only in birds. In long-lived birds, pair bonds may persist for several seasons in some species, while in others mate change occurs even when both partners are still alive. Here, we test predictions from the adaptive hypotheses for divorce, using long-term data (15 years) on mate change and reproductive success in a long-lived shorebird, the dunlin
Calidris alpina. We found that about one quarter of the pairs divorced (23% of 126 breeding attempts). Among the divorcing females, six changed partner more than once (one female changed partner three times). Following divorce, females dispersed longer than males. Start of egg-laying (presumably reflecting arrival time to the breeding ground), previous breeding success, and male age or size did not seem to influence the occurrence of divorce. However, females that changed mate between consecutive breeding attempts achieved higher reproductive success. Moreover, this improvement appeared independent of breeding experience. Since we were unable to detect any effect of divorce on male reproductive success, our results suggest that divorce in the dunlin is best explained by the better option hypothesis.