Reproductive success in female mountain goats:: the influence of age and social rank

In mammals, reproductive success may be positively correlated with both maternal age and social rank. Because social rank often increases with age, however, the effects of rank and age on reproductive success are difficult to separate. We studied a marked population of mountain goats, Oreamnos americanus, to assess the relative effects of maternal age and social rank on kid production and survival. Adult females formed a linear and stable dominance hierarchy. Kid production increased with both age-specific maternal social rank and age, but decreased slightly after 9 years of age. The influence of dominance was particularly important among 3- to 5-year-old females, and the positive effect of dominance on kid production decreased with increasing female age. Age-specific social rank and maternal age did not affect kid survival to autumn or to 1 year. Kids whose mothers were heavy for their age had a higher probability of surviving to weaning and to 1 year than kids born to light females. When age was accounted for, female survival was not related to social rank. Social rank appears to be an important determinant of reproductive success for female mountain goats, especially among young females. (C) 2001 The Association for the Study of Animal Behaviour.