Investigating population performance and factors that influence reproductive success in the eastern black rhinoceros (Diceros bicornis michaeli)
The aim of this research was to determine the sustainability of European captive population of eastern black rhinoceros, and investigate factors that may influence population performance.
With fewer than 5,000 black rhinoceros remaining, ex situ populations play a vital role in the conservation of this species. However, to fulfil this role, populations must be self-sustaining. The aim of this research was to determine the sustainability of European captive population of eastern black rhinoceros, and investigate factors that may influence population performance.
Although this population is self-sustaining, growth rates are low compared to in situ counterparts and below the target 5% growth per annum. Performance is limited by sub-optimal reproduction, with individuals producing fewer calves per annum, and a high proportion of individuals failing to reproduce. To investigate differences in reproductive success, faecal samples collected from 90% of the population were analysed for reproductive and adrenal hormone metabolites, to investigate differences between breeding and non-breeding individuals.
In females, irregular oestrous cyclicity was observed, with longer than average cycles observed more frequently in non-breeding females, and acyclic periods more common in females that had not bred for at least seven years. Irregular cyclicity was also associated with elevated glucocorticoid concentration. Non-breeding females also had higher body condition scores, and were less likely to exhibit regular signs of oestrus. Non-breeding males had lower faecal testosterone than males that had previously sired offspring. Extrinsic factors related to the social and physical environment were investigated, but no consistent relationships were observed between breeding and non-breeding males or females.
In summary, intrinsic differences in reproductive hormones have been identified in both males and females, which may be related to differential reproductive success.