The effects of animal transfers on the reproductive success of female white rhinoceroses (Ceratotherium simum simum) kept in European zoos

The Southern white rhinoceros (Ceratotherium simum simum) has been kept in European zoos since the 1960s. However, captive breeding success has been low, with social group composition, group size, and available space all playing a role. Female rhinoceroses that have never bred or not bred for a long time have a particularly increased risk of developing reproductive tract pathologies, often resulting in infertility at a young age. One management measure to stimulate breeding is to transfer non-reproducing animals to other zoos. This study evaluated the success of transfers of 4 – 28 years old white rhinoceroses between European zoos. We analyzed n = 90 (45 males and 45 females) transfers of white rhinoceroses between 1990 and 2018. Fecal progesterone metabolite levels were analyzed for a subset of female rhinoceroses. The success of a transfer was defined as a calf born within five years. The success rate after female transfers was 26.7%; however, when the age limit of transferred females is set at 18 years, the success rate was 44.4%. The success rate after a male transfer was 23.2%. In transferred females, 83% of births occurred within three years after a transfer. Births following the arrival of a new male were distributed over five years. After a male transfer, endocrine data were determined in 26 of 82 females affected by the transfer. Positive development of estrous cycle activity after the arrival of the new bull occurred in 13 females. In summary, the success of the transfers in terms of offspring birth and endocrine stimulation of cycle activity was lower than anticipated, and sometimes a considerable amount of time elapsed before a calf was born. Nonetheless, transfers are essential to promote breeding. The relatively low success of the transfers analyzed in this study relates to the partially advanced age of the white rhinoceroses studied. Transfers of juvenile or adolescent females currently conducted between European zoos reveal a better birth rate than the present study.