Divorce rate in birds increases with male promiscuity and migration distance

Abstract

Socially monogamous animals may break up their partnership after one breeding season by a so-called divorce behaviour. Divorce rate immensely varies across avian taxa that have a predominantly monogamous social mating system. Although a range of factors associated with divorce have been tested, there is not a consensus regarding the large-scale variation and relationships among associated factors. Moreover, the impact of sexual roles in divorce still needs further investigation. Here, we applied phylogenetic comparative methods to analyze one of the largest datasets ever compiled that included divorce rates from published case studies of 232 avian species from 25 orders and 61 families. We tested correlations between divorce rate and a group of factors that are closely related to pair bond strength: promiscuity of both sexes, migration distance, and adult mortality. Our results showed that only male promiscuity, but not female promiscuity, had a critical relationship with divorce rate. Furthermore, migration distance was positively correlated with divorce rate and indirectly affected divorce rate via male promiscuity. These findings indicated that divorce might not be simply explained as an adaptive strategy or neutral occurrence, but could be a mixed response to sexual conflict and stress from the ambient environment.