Social influences on contact maintenance interactions of bison mothers and calves: group size and nearest-neighbour distance

Green, Wendy

If predation risk for young animals varies with the number and proximity of conspecifics in gregarious 'follower' ungulates, mothers and offspring should maintain closer contact in smaller groups and when further from neighbours. This hypothesis was supported by evidence of intra- and inter-individual variation in bison mother-calf interaction. Dyad members spent more time close together, following each other and synchronizing their behaviour in smaller groups and when nearest-neighbour distance was greater. Comparisons of maternal and filial contribtions to observed patterns indicated that calf behaviour varied more with social conditions than that of mothers. Calves followed mothers more in smaller groups. Resting calves waited longer to follow their grazing mothers when other conspecifics were nearby. Thus dyad members, particularly calves, behave as if the presence of conspecifics offers protection. The results also indicate a second benefit of gregariousness: calves spent half as much time active in large as in small groups. This suggests that larger groups by allowing a relaxation of contact maintenance confer energetic as well as protective advantages. One proposed benefit, that calves grow faster in larger groups, was not supported; growth rates were not significantly related to group size when other variables, particularly birth date, were included. A second proposed benefit, that large groups reduce lactation costs, remains to be tested.

Social influences on contact maintenance interactions of bison mothers and calves: group size and nearest-neighbour distance

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