Divorce in the long-lived and monogamous oystercatcher, Haematopus ostralegus: Incompatibility or choosing the better option?

Oystercatchers breeding on Schiermonnikoog divorced, because one of the mates deserted (leaving the partner as a victim of its choice), or because one or both mates were chased from the territory by usurpers. Though the majority of divorced birds were classified as victims, among birds that retained breeding status females more often chose to divorce than did males. Females changing mates were also more likely to move between territories than were males. A much larger database from Skokholm showed that the reproductive success of new pairs, which depended on the breeding history of the female only, was lower than that of old pairs. The suggestion that females benefited from divorce depended on the interpretation of the decrease in reproductive success with the new mate for widowed birds as an efficiency cost of mate change. However, the increase in reproductive success with duration of the pair bond for female first-time breeders and divorced females (but not for widowed females) may be linked to an increase in breeding age of the female, instead of a re-bound from initial inefficiency in reproduction with the new mate. Hence, competition for good mates and/or good territories appears the primary constraint on options for mate change for both males and females. The role of active choice and competition for good mates and/or good territories has been neglected in previous studies of divorce. The better option hypothesis takes account of both.