, Volume 9, Issue 1, pp 23-33

Structure of association in impala, Aepyceros melampus

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Summary

  1. The associatons and movements of 400 marked impala of known age were studied in the Sengwa Wildlife Research Area, Zimbabwe, from May 1975 to May 1978.

  2. Female and juvenile impala were dispersed in a clan system. The average level of association (measured by Sorensen's index) between members of the same clan was 0.27 and between members of neighbouring clans 0.02. There was no significant correlation between separation of individuals' centres of home range and association within clans.

  3. The associations of impala were summarised in a maximum spanning tree. Females emerged as a uniform and discrete group without sub-groups or families, but young adult females of the same clan associated preferentially with their peers of equal age. No dominance hierarchy or consistent leader was detected among females, although animals 5 years and older were more likely to move independently.

  4. A numerical method for calculating coefficients of relatedness in a clan, or large social group, is described (Appendix). The average level of relatedness between impala peers is estimated to be higher than between individuals one or more years apart in age. It is suggested that this may influence the association pattern.

  5. Non-juvenile males did not have a stable social structure, and their associations were more open than those between females, from whom they were frequently segregated. Young and old males associated preferentially by age, but middle-aged males avoided each other. This variation is related to different developmental requirements, particularly learning about male-male interactions by young animals and expression of dominance by middle-aged animals.