To Synchronise or Not to Synchronise: A Dilemma for Young Bighorn Males?

Bighorn sheep (Ovis canadensis) are sexually dimorphic and live in nursery groups, bachelor or mixed groups. To remain in a group, individuals have to synchronise their activity according to the type of group they are in, which may incur a cost for individuals of different body size from the other group members. To test this hypothesis, I calculated the degree of synchrony of activities for each individual within a group. Animals in nursery or bachelor groups were highly synchronised with each other while mixed-age-sex groups had the lowest group synchronisation index. Two and three-year old bighorn males are intermediate in body size between the two adult sexes. Two-year-old males always adjusted their behaviour independent of group type, while three-year-old males synchronised their behaviour when with bachelor, but less so when in nursery groups. I suggest that two- and three-year-old males may face a conflict between synchronising their behaviour to stay in a group and the need to forage according to their own time budgets. I conclude that intermediate-sized young male ungulates of sexually dimorphic species may be better off forming same-sex-age groups.