Abstract

The Birmingham Zoo is working toward managing four bull African elephants as a single bachelor group. This had not been attempted previously in the United States, and it was unknown if competition or a lack thereof would influence antagonistic behavior or serum testosterone concentrations. Keeper safety also was a concern, and methods for anticipating behavioral and endocrine changes in the bulls were desired. To measure dominance, the bulls were each observed for a total of 9.5–7.9 hrs while on exhibit in pairs or trios. Dominance was determined using the percentage of the total antagonistic interactions that resulted in a “win” for each bull in every dyad, which then was organized in a dominance matrix. To measure tractability, keepers rated the bulls’ performance during daily training exercises. Blood was collected weekly, and testosterone was measured by enzyme immunoassay. A dominance hierarchy evolved in which the largest bull is most dominant, but he is followed by the second smallest bull, followed by the second largest and the smallest bulls together at the base. This result is different from wild, non-musth bulls whose dominance is correlated with size. Mean testosterone concentrations differed between only the oldest bull and the youngest bull (p<0.05), and therefore appear not to be related to dominance. There was no correlation (p>0.05) between testosterone concentrations and daily ratings of tractability. Testosterone levels that might be considered indicative of musth were not observed, so the possibility for tractability to diminish in association with testosterone fluctuations of that magnitude still exists.