To benefit from compounding growth, it is important to maintain rhino populations at productive densities, and prevent the density-dependent declines in reproductive performance (lengthening inter-calving intervals, older ages at first calving, reduced calf survival, increased mortality rates etc.) that can occur if rhino populations are left to approach or exceed ecological carrying capacity (ECC). It is recommended that populations be kept productive by annually translocating at least 5% and not more than 8% of populations that have exceeded 50% of estimated ECC annually. In smaller populations, it is recommended that densities should not be allowed to exceed 75% of ECC. Techniques exist to estimate ECC for black rhino and these are continually being refined. The impact of potential competing browsing species such as elephants, giraffe and nyala, as well as the impact of any vegetation changes for rhino, also need to be considered.
Surplus rhinos that are removed from more heavily stocked populations are used to create new or enhance existing populations with a good potential for high growth. Apart from the strategic benefit of having more eggs in more baskets, translocations aim to improve or maintain performance in established populations, whilst at the same time to create new rhino investments with rapid growth potential. Due to the effects of compounding, small differences in rhino metapopulation performance translate to large differences in numbers of rhinos in only a few years, which is why so much effort is expended in trying to keep rhino populations productive.
Regular monitoring and reporting on the reproductive and demographic performance of populations using standardised systems, provides managers with the necessary information to make more informed and better biological management decisions, as providing measures of whether or not metapopulation management goals are being met. Monitoring the reproductive performance of females and accurately estimating rhino numbers are two key aims of monitoring. Regional synthesis of the results of this monitoring also enables managers of a park to put the performance of their rhino population in context, as well as learn and share lessons from past experience, which in turn can be used to further refine best-recommended management practices. Continental rhino monitoring training courses have been developed by the AfRSG and these focus on training local trainers so they can train local staff on site.
Richard EmslieScientific OfficerIUCN SSC AfRSG