Divorce and extrapair mating in female black-capped chickadees ( Parus atricapillus ): separate strategies with a common target

Abstract

Patterns of divorce and extrapair mating can provide insights into the targets of female choice in free- living birds. In resident, site-faithful species with contin- uous partnerships, the better options and the incompati- bility hypotheses provide the most likely explanations for divorce. Extrapair mating can be explained by a num- ber of hypotheses often making similar predictions. For example, the good genes and future partnerships hypo- theses predict similar patterns if males with good genes also make the best future partners. By considering both divorce and extrapair mating, it may be possible to dis- tinguish between these comparable hypotheses. We ex- amined natural patterns of divorce and extrapair mating in a long-term study of black-capped chickadees ( Parus atricapillus). Out of 144 partnerships over 8 years, we observed 11 divorces and 38 faithful pairs between sea- sons. Females usually divorced between their first and second breeding seasons for males of higher social rank than their previous partners, had similar reproductive success prior to divorce as females who retained their previous partners, and did not divorce on the basis of previous reproductive success. These results confirm earlier experimental evidence that females divorce for better options. Females who divorced were significantly more likely to have had mixed-paternity broods prior to divorce than females who stayed with their previous partners. There was no evidence that females divorced in favour of previous extrapair partners. These results sup-