VIGILANCE, GROUP-SIZE AND SOCIAL-STATUS IN CAPYBARAS

Capybaras, Hydrochaeris hydrochaeris, live in groups of varying size a veraging 10 adults of both sexes. Vigilant behaviour was studied in ca pybaras under natural conditions, using focal-animal sampling on indiv idual females, dominant males and subordinate males from groups of dif ferent sizes. There was a significant negative correlation between gro up size and individual alert rate, and a positive correlation with tot al group alert rate. Although the reduction in individual rates of vig ilance levelled off at group sizes of 9-10, total alert rate continued to increase. The behaviour of the females accounted for most of the v ariation in individual alert rate and the behaviour of subordinate mal es accounted for most of the variation in total alert rate. These resu lts suggest that females benefit the most from being in larger groups due to reduced vigilance required, while subordinate males 'pay' for t heir group membership by the vigilance they perform.