A captive population in crisis: Testing hypotheses for reproductive failure in captive-born southern white rhinoceros females

The captive southern white rhinoceros (Ceratotherium simum simum) population is not self-sustaining. Many founders reproduced, but reproduction among captive-born (F1) females has been extremely sluggish. Thus the conservation breeding program for this species faces a looming crisis. Using behavioral observations of a large captive population and a questionnaire survey circulated to facilities worldwide, several hypotheses for F1 female reproductive failure were evaluated. Counter to predictions regarding behavioral deficiency in sociosexual behaviors, F1 females were at least as proficient as F0 females for all behavioral measures. Males also showed no sociosexual preferences for F0 over F1 females. Results indicate that most reproductive failure occurs post-copulation. The reigning root-cause hypothesis for F1 female reproductive failure postulates that F0 females are behaviorally dominant and suppress reproduction in F1 females. However, no evidence for behavioral dominance was found and F1 females housed with F0 females were more likely to reproduce than those housed without F0 females. Such social facilitation of reproduction is beneficial to F1 female reproduction, but does not explain differential reproduction between F1 and F0 females. Because the design controlled for current conditions, these results point to development in captivity as the root cause of postcopulatory reproductive failure in F1 females.