Sex-specific fitness consequences of mate change in Scopoli's shearwater, Calonectris diomedea

Social monogamy is the most common social mating system in birds. However, the persistence of pair bonds between breeding seasons varies among species, populations and individuals. Understanding fitness causes and consequences of mate change is critical for understanding population dynamics and the evolution of social monogamy. We used 12 years of data from Scopoli's shearwater breeding population to estimate mate change probabilities and test whether they affect the probabilities of (1) skipping breeding, (2) apparent survival and (3) breeding success. Widowing was the most common cause of mate change, with more males changing mates at least once in their lives than females. Females' probability of skipping a breeding season increased significantly just before pairing with a new partner. Also, we found that females' apparent survival, but not males', might increase after mate change. A possible explanation is that a longer adult life expectancy of females after mate change could at least partially offset the cost of skipping breeding. We found no relation between mate change and breeding success. Our study suggests that the costs and benefits of mate fidelity may be sex specific in this species. Future research on this topic should focus on the effects of mate change on each sex's lifetime reproductive success, which we could not address specifically in this study. Future studies will hopefully be able to delve deeper into how mate change, caused by divorce or widowhood, shifts the balance of reproduction or survival, determining lifetime reproductive success. & COPY; 2023 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.