THE DEVELOPMENT OF INDEPENDENCE IN BISON - PREWEANING SPATIAL RELATIONS BETWEEN MOTHERS AND CALVES

Contact-maintanance interactions between bison, Bison bison, mothers and calves during the first 7 months were observed to examine spatial aspects of the development of independence. During the first week, dyad members maintained close contact; however, by week 2 distances increased abruptly as calves followed their grazing mothers less often. Dyadic interaction changed little after week 2; subsequent changes in calf behaviour appeared to be related more to calf maturation because they were not accompanied by changes in mother-calf distance or frequencies of approaching and leaving, and were in a direction opposite that expected with increasing independence. Around month 3 many changes occurred: calves suckled and rested less, vocalized more, and increasingly grazed with and followed or led mothers. Consorting bulls caused temporary increases in dyadic distance and filial independence during month 4. Developmental changes occurred in the synchrony between mother and calf movements and activity patterns, and in vocalization frequencies. In contrast, mother-calf distance and approaching/leaving frequencies showed little change; thus these measures appear less appropriate for studies of ungulates than for those of primates. Dyadic interaction was characterized by greater independence than might be expected in follower species, where maternal proximity may be the primary means of protecting young from predators. For example, mothers were least often nearby when calves appeared most vulnerable. Bison are clearly followers in that mothers and calves often rest close together and maintain close contact during the first week. Contact maintenance also resulted primarily from filial behaviour. The presence of the herd appears to modify the follower pattern, incorporating elements of hiding behaviour and accelerating filial independence. © 1992 The Association for the Study of Animal Behaviour.