| dc.description.abstract | In many species, such as the Scimitar-horned oryx (Oryx dammah) , high levels of inter-male aggression plague attempts to-maintain bachelor herds in captivity. At Fossil Rim Wildlife Center, two groups of 5 male oryx were treated with hormonal implants in an attempt to reduce aggression, with one receiving melengestrol acetate (MGA) and the other a GnRH agonist. At 1-yr post-implantation, the following aspects were examined: (1) the effectiveness of the implants in controlling aggression, (2) the relationship among plasma testosterone, dominance, and aggression, and (3) influences such as the presence of female-typical hormones (progestins) in males, shortened horns in the MGA-implanted group, and possible depressant effects of MGA on inter-group differences in aggression. At 1-yr post-implantation, three types of behavioral data were collected: (1) frequency of social actions using an all-occurrences recording technique; (2) activity state using scan sampling with instantaneous recording at 15-min intervals, and (3) association in terms of subgroup size at 15-min intervals. Within all categories of agonistic behavior, the mean number of acts was significantly lower in the MGA-implanted group than in the GnRH agonist-implanted group (p=0.0001). Between groups, there was no significant difference in plasma testosterone concentrations at 1-yr post-implantation (p=0.1172). Over all individuals, there was no significant correlation between plasma testosterone and frequency of ritualized threats (p=0.93) or non-ritualized aggression (p=0.86). The MGA-implanted group displayed significantly lower levels of all social behaviors (p=0.0001), a significantly lower index of association (p=0.0001), and a significantly higher index of resting (p=0.0001). At 1-yr post-implantation, the MGA implants were more effective in controlling aggression, but the lower levels of aggression could not be attributed solely to depressed plasma testosterone, a "feminizing" effect of MGA, or shortened horns in the MGA-implanted group. The MGA appeared to reduce the frequency of all social behavior, including aggression, and general activity. | en |
