Are social factors sufficient to explain sexual segregation in ungulates?

As a general rule ungulates that are sexually dimorphic in body mass live in separate groups of males and females throughout the year, except during the breeding season, a behaviour known as sexual segregation. Many hypotheses have been developed to explain sexual segregation and most have failed to demonstrate segregation in ungulates under controlled conditions. We experimentally examined a key hypothesis in a sexually dimorphic ungulate, the Soay sheep, Ovis aries, using a maze design. The social factors hypothesis states that animals of the same sex or cohort are more likely to interact with same-sex or same-age peers than with animals of different sex or age because of differences in behaviour caused by different roles in reproduction or to avoid agonistic interactions with animals of different size. Both males and females preferred the company of peers of the same sex or of their own group. The attraction towards an animal of the same sex was not driven by an aversion to animals of a different sex, as the social factors hypothesis proposes. We conclude that these preferences in aggregation patterns for animals of the same sex can contribute to the cohesion of single-sex groups and promote segregation, although additional factors are needed to explain the patterns of sexual segregation observed in nature. We comment on these results from an evolutionary perspective.