Translocation and range expansion is an important strategy for white and black rhinoceros conservation to ensure effective growth rates in these near threatened and critically endangered species, respectively, by providing habitat for population growth. In order to establish viable populations, the success relies on post-release survival and reproductive efficacy. Here, we report birth rates and birth-sex-ratios in 51 female black (Diceros bicornis) (BR) and 18 female white (Ceratotherium simum) (WR) rhinoceroses translocated between 2004 and 2019. Blood samples were collected from these animals at capture or release and serum progesterone concentrations analysed using a chemiluminescence method. Birth and sex-ratios were recorded for 18 months after translocation. Rhinoceroses were classified as “non-pregnant” (1-4.4 nmol/L, BR=17; WR=2), “3-4 months pregnant” (4.5-6 nmol/L, BR=3; WR=2), “5-8 months pregnant” (7-50 nmol/L, BR=14; WR=5), “9-12 months pregnant” (50-70 nmol/L, BR=9), and “13-16 months pregnant” (70-≥90 nmol/L, BR=3), based on their progesterone concentrations. None of the BR or WR classified as “luteal activity” and of the BR classified as “3-4-months pregnant” gave birth. Only seventeen BR, classified as “5-8-months pregnant” or higher (65 % of these classifications), gave birth to ten male (59 %), five female (29 %) and two calves of unknown sex, respectively. Post-mortem examination on one BR from this classification indicated a recent abortion. Only one WR classified as “3-4-months pregnant” (50 %) gave birth to a female calf and four WR classified as “5-8-months pregnant” (80 %) gave birth to three male and one calf of unknown sex. Results indicate that translocation-stress might disrupt early- to mid-term pregnancies in rhinoceroses and possibly cause a sex-ratio bias towards male calves. Both observations could be related to the cortico-adrenal stress response and require further investigation.
Anna Sickmüller (Fri,) studied this question.