Approximately 10% of the global population of eastern black rhinos are part of the European zoos. However, the population is only just sustainable with low birth rates and reproductive skew limiting their breeding potential. We aimed to look at factors that may be influencing the reproductive success and skew of the population.
89% of females in the European endangered species breeding programme were divided into three age groups; immature, post-reproductive and reproductive (never produced a calf, produced a calf more or less than seven years ago).
Almost 10,000 faecal samples were taken for hormone analysis at Chester Zoo’s endocrinology lab. Each individual was assigned a body condition score ranging between one and five (1=thin/5=heavy) using standardised photographs or direct observations and keepers recorded behaviours associated with a female rhino coming into oestrous.
We found that not only do non-proven breeding females display irregular cyclicity, often by displaying longer cycles, but they are also less likely to exhibit behavioural indicators of oestrus and have higher body condition scores.
These results offer important insights into measures that can be taken to minimise reproductive skew, such as using more reliable methods to predict oestrus and maintaining lower body conditions scores for females. In the long run, this will help to maintain the sustainability of the European zoo population by potentially boosting reproductive performance.
Edwards, K. L., Shultz, S., Pilgrim, M., & Walker, S. L. 2014. Irregular ovarian activity, body condition and behavioural differences are associated with reproductive success in female eastern black rhinoceros (Diceros bicornis michaeli). General and Comparative Endocrinology.