The behaviour of a wild population of tassel-eared squirrels was investigated from September 1969 to January 1971. Squirrels were live captured and marked for individual recognition. Adult squirrels were generally non-gregarious throughout the non-mating season. During the mating season (April and May) periodic bouts of sexual activity occurred involving interactions between an oestrous female and a group of socially ranked males. The most dominant male in each mating bout was first to copulate with the female. Aggressive behaviour in males was also positively correlated with the frequency of copulation. Male dominance hierarchies were characterized by non-linear arrangements and were relatively unstable over bouts. Certain males tended to be dominant in their own home areas with females from the same areas.