SEXUAL DIMORPHISM IN THE GREATER ONE-HORNED RHINOCEROS (RHINOCEROS-UNICORNIS)

To assess sexual dimorphism in the greater one-horned rhinoceros (Rhinoceros unicornis), morphometric data were collected from 50 free-ranging individuals in Royal Chitwan National Park, Nepal. Twenty-two mensural and 16 nonmensural characters from 43 anesthetized individuals and seven carcasses, representing 4% of the entire wild population, provided the basis for this analysis. Adult males and females differed significantly in only a few of the mensural characters. Adult males developed significantly longer mandibular incisors and significantly greater neck musculature than females. Long incisors (rather than horns), powerful neck and shoulder musculature, and extensive neck and shoulder skin folds figured prominently in fights and displays between breeding-age males. Males born in zoos often are > 25-cm taller at the shoulder and considerably larger in mass than females. Reduced size dimorphism in free-ranging animals, as observed in this study, may be explained by greater stress on males and poor nutrition during the long nonbreeding interval when young adults are harassed by dominant males and are excluded from prime grazing areas.