Post-weaning associations among bison mothers and daughters

Abstract

For gregarious ungulates, associations between mothers and their adult daughters may play an important role in the organization of social groups. We examined the spatial relations of bison, Bison bison, mothers and daughters during the first 3 years to determine whether dyads continue to associate after weaning and, if so, which member of the dyad is primarily responsible. Between weaning and the birth of the mother's next calf, most daughters spent 1 or 2 months in temporary separation from their mothers. This separation did not appear to result from maternal aggression since mothers showed less aggression in the second half of the nursing period than in the first. Mothers and daughters continued to associate after the mother's next calf was born, though less closely than before. In their second and third years, weaned daughters spent more time in groups with their mothers than with randomly chosen control cows. Mothers and daughters also approached and followed each other more frequently, and spent more time near each other, than did daughters and controls. The weaned yearlings of parturient cows spent less time in close proximity to their mothers than did the nursing yearlings of barren cows. However, both groups showed similar frequencies of contact maintenance behaviour. Post-weaning shifts in spatial relations involved increasing filial independence and increased maternal efforts at contact maintenance. The closeness with which dyads associated after weaning was positively correlated with maternal contributions to maintenance of proximity. Daughters benefited from post-weaning association in that they spent more time in the centre of groups and were less often displaced by other animals when their mothers were in the group than when they were not.