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Abstract

Effects of maternal age and experience on long-term contact maintenance interactions with female offspring were examined in bison (Bison bison), as part of a study of factors influencing dyadic behavioural interaction. During the first five months, patterns of change in interactions varied with maternal age and parity. Young (largely primiparous) mothers and their calves steadily increased the frequency with which they maintained contact, while older mothers and their calves became increasingly independent (e.g. calves walked away from mothers more and followed them less often). Filial independence was most extreme in the (last) calves of the two oldest mothers. These age-specific patterns appeared to result largely from contrasting shifts in maternal behaviour from Month 1 to 2; differences between groups before and after this shift were opposite in direction. In the first month, older mothers maintained more frequent contact and were behaviourally more synchronized with their calves. After the first month, however, the efforts of older mothers to maintain dyadic proximity abruptly decreased, while those of young mothers and their calves gradually increased. Subsequent differences between groups were more consistent. Young mothers and their daughters maintained closer contact and continued to do so well past weaning, at least as late as the third year, when daughters reached sexual maturity. Filial behaviour played an important role in determining patterns of dyadic spatial relations; the close proximity maintained by young mothers and their offspring appeared due largely to the frequency with which these calves followed their mothers' movements. The relatively independent calves of older mothers took greater initiative in contact interactions with mothers (e.g. nosing, licking). Young mothers appeared to strengthen long-term bonds with daughters by initiating contact frequently; the closeness of post-weaning dyadic association increased with the frequency of pre-weaning maternal contact.