Rothstein, Aron and Griswold, Joseph G. 1991. Age and sex preferences for social partners by juvenile bison bulls, Bison bison. Animal Behavior 41: 227-237
Social interactions initiated by male calves and yearlings were examined to test predictions arising from two hypotheses concerning the function of juvenile social interactions. Subjects showed a preference for partners within their own age classes. Yearlings, but not calves, distinguished between male and female partners: they were more aggressive with males and initiated more olfactory investigations with females. The absence of sex-related weight differences within age classes suggests that partner preferences were based on sex rather than body mass. The results support the hypothesis that juvenile interactions in bison function as motor training for future behavior rather than as competition for present resources. The choice of social partners by young bulls allows them to participate in vigorous encounters resembling those of adult bulls, while not being handicapped by large differences in size or competence. Experience gained in these interactions could be important when a bull reaches physical maturity and is competing for oestrous cows.