Rothstein, Aron. 1988. Social Organization in Juvenile Bison Bulls (Bison bison): Non-linear Dominance and Dyadic Associations. PhD dissertation. The City University of New York. 99 p.
Interspecific comparisons of social development suggest that the types of social interactions engaged in by juveniles may be related to the adult social organization. The objective of this study, conducted at Wind Cave National Park in South Dakota, is to describe the social behavior and organization of juvenile bison bulls (Bison bison). Based on the social behavior of adult bulls, it is predicted that juvenile bison bulls will form an aggressively interacting social sub-group within the cow/juvenile herd.
Calf and yearling bulls were found to interact preferentially with social partners of their own age. Yearlings also interact more than expected with 2-year-old females. It appears that young males choose partners of their own size. The juvenile males interacted more aggressively with male than with female partners.
Dominance relations among the yearling males were investigated using several methods. The yearlings have stable dyadic relationships without an overall linear order. Significant transitivity in the relationships suggests that a combination of physical attributes and social experience is responsible for the outcome of agonistic interactions. There is a correlation between dominance and horn size.
A method is developed and used to analyze pair association data for the 16 male yearlings. Dyadic associations were found among the yearlings, representing pairs that were in the same group and/or interacted more than expected under the hypothesis of random association. These relationships involved 15 of the 16 individuals. Yearlings were more likely to associate with partners of differing dominance rank than with rank neighbors. Because these pairs have well established dominance relationships, they may be able to engage in vigorous agonistic interactions with reduced chance of escalation and injury.
Young bulls form a sub-group within the herd. They interact with each other in ways that maximize their experience in intermale agonistic encounters and minimize the risks involved in serious fights. This picture of yearling bull social organization is consistent with the hypothesis that the pattern of male bison social development should reflect the social structure among adult bulls and not the structure of the cow/juvenile herd into which they are born.