The nature and consequences of mother-daughter associations in naturally and forcibly weaned bison

Bison (Bos bison) mothers and daughters have a stable association that may persist beyond weaning, whereas no such extended relationship exists between mothers and sons. The practice of forced weaning of bison in Antelope Island State Park, Utah, provided the opportunity to experimentally investigate the nature and consequences of postweaning mother-daughter associations. Forced weaning changes the early social environment of calves and may disrupt social organization by eliminating mother-daughter associations. We compared the mother-daughter associations of forcibly weaned female yearlings, following release back into the population, with those of naturally weaned female yearlings. Yearlings that had been forcibly weaned as calves did not reassociate with their mothers following winter separation. Forcibly weaned yearlings spent no more time with their mothers than with randomly chosen adult females. Naturally weaned yearlings had a significantly stronger association with their mothers, were displaced less often by other herd members, and spent more time in the centre of groups than forcibly weaned yearlings. We were unable to detect benefits to naturally weaned daughters in terms of growth and age at first reproduction. Mothers of naturally weaned yearlings did not differ from mothers of forcibly weaned yearlings in subsequent mass change or reproduction.