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.