Sexual segregation in fallow deer: are mixed-sex groups especially unstable because of asynchrony between the sexes?

In gregarious ruminants, females and males tend to live in separate groups outside the rutting season. According to the 'activity budget' hypothesis, this is due to an activity asynchrony between the two sexes reducing the lifetime of mixed-sex groups. We tested this hypothesis in a fallow deer population. Activity asynchrony was more frequent in mixed-sex than in single-sex groups. In addition, mixed-sex groups had a higher probability of splitting-up than all-female groups, and they mainly split up into single-sex groups. However, activity asynchrony did not appear as a major cause of splitting-up.