Aggression, dominance, and mating success among capybara males (Hydrochaeris hydrochaeris)

Social groups of capybaras, Hydrochaeris hydrochaeris, averaging 10 adults contained a mean of 3.6 adult males. Of 2911 interactions observed within social groups of capybaras, 34% were among adult males, and these were invariably aggressive. Males were organized in stable, linear hierarchies. The dominant male in each group was significantly heavier than any of the subordinates, but among subordinates, status was not correlated with weight. The dominant male maintained a central position at the core of the group, and time spent in the group by males was correlated with their social status. Each dominant male secured significantly more matings than did each subordinate, but subordinate males, as a class, were responsible for more matings than was each dominant male. Regarding alarm calls, although each subordinate male called less on average than the dominant, subordinates were responsible for the majority of alarm calls in a group. The stability of these hierarchies, in one case over 3 years, and the tendency for males to move up the social ladder in an orderly queue, suggest that many males are unlikely ever to secure dominant status. © 1993 International Society for Behavioral Ecology.