Fecal corticosterone concentrations and reproductive success in captive female southern white rhinoceros

Prolonged or frequent secretion of adrenal glucocorticoids in response to aversive stimuli can negatively impact reproduction. Because female southern white rhinoceros (Ceratotherium simum simum) reproduce poorly in captivity, we compared fecal corticosterone metabolite concentrations among parous, nulliparous, and adolescent females and examined social and physical aspects of the captive environment that might be related to differences in corticosterone metabolite concentrations. Aggression, dominance, sexual and play interactions, social group size and composition, enclosure size, and other housing characteristics were assessed though behavioral observations and review of historical and institution records. Concentrations of metabolized corticosterone in fecal samples were analyzed by enzyme immunoassay. The proportion of nulliparous females did not differ (p > 0.05) between subordinate and dominant animals, and subordinates did not have a higher mean fecal corticosterone concentration than dominants (p > 0.05). Of the behaviors examined, only the frequency of sexual play behaviors differed (p < 0.05) between dominants and subordinates. Average corticosterone concentrations differed (p < 0.05) across housing institutions but were not consistently elevated (p > 0.05) for females housed in most of the environmental conditions assessed. Housing with a female companion known from adolescence, however, tended to be associated (p = 0.06) with a lower mean corticosterone concentration than that when housing with a female companion introduced during adulthood or no female companion. Wild-caught females had a higher (p < 0.05) average corticosterone concentration than captive-born females. Average corticosterone concentration did not differ (p > 0.05) between acyclic and cycling, or nulliparous and parous females.

Research highlights
► Nulliparous females were not more likely to be subordinate than parous females.
► Subordinate females engaged in sexual play more often than dominant females.
► Average corticosterone was not affected by dominance.
► Average corticosterone was higher in wild-caught than in captive-born females.
► Females housed with well-known companions tended to have lower mean corticosterone.