Divorce rate in birds increases with male promiscuity and migration distance

Socially monogamous birds may break up their partnership 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, broad-scale drivers of divorce rate remain contentious. Moreover, the impact of sexual roles in divorce still needs further investigation due to the conflicting interest of males and females. Here we applied phylogenetic comparative methods to analyse one of the largest datasets ever compiled that included divorce rates from published studies of 186 avian species from 25 orders and 61 families. We tested correlations between divorce rate and a group of factors: 'promiscuity' of both sexes (propensity of polygamy), migration distance, and adult mortality. Our results showed that only male promiscuity, but not female promiscuity, had a positive relationship with divorce rate. Furthermore, migration distance was positively correlated with divorce rate, while adult mortality rate showed no direct relationship with divorce rate. These findings indicated that divorce might not be a simple adaptive (by sexual selection) or non-adaptive strategy (by accidental loss of a partner), but could be a mixed response to sexual conflict and stress from the ambient environment.