Population parameters, performance and insights into factors influencing the reproduction of the black rhinoceros Diceros bicornis in Namibia

Estimating the population parameters, performance and factors that influence reproduction from long-term, individual-based monitoring data is the gold standard for effective wildlife management and conservation. Yet this information is often difficult and costly to collect or inaccessible to managers. We synthesized a 20-year set of individual-based monitoring data from a subset of black rhinoceros Diceros bicornis subpopulations across a range of environmental conditions in Namibia. Our findings demonstrate that despite the relatively arid landscape in Namibia, the black rhinoceros metapopulation is performing well, measured by age at first reproduction, inter-birth interval, population growth and survivorship. Information-theoretic modelling revealed that a univariate model including normalized differential vegetative index had a greater influence upon age at first reproduction than population density. The inter-birth interval model set identified cumulative rainfall during the 15 months prior to the birth month as the top model, although the mean normalized differential vegetative index during the inter-birth interval was comparable. There was little evidence for density-dependence effects on reproduction. These findings suggest that although browse quality could have a greater impact on parameters spanning multiple years, shorter-term parameters could be more influenced by rainfall. Our analysis also revealed a synchronous pattern of conceptions occurring in the rainy season. Our study provides a set of population parameter estimates for Namibian black rhinoceros subpopulations and preliminary insights on factors driving their reproduction. These expand our collective knowledge of global black rhinoceros population dynamics and improve our confidence and capability to adaptively manage the black rhinoceros metapopulation of Namibia.

Automated summary

Estimating population parameters, performance, and factors influencing reproduction from long-term monitoring data is crucial for effective wildlife management and conservation. In this study, we synthesized 20 years of individual-based monitoring data on black rhinoceros in Namibia and found that the metapopulation is performing well despite the arid landscape. Information-theoretic modeling revealed the influence of vegetation index on age at first reproduction and rainfall on inter-birth interval, indicating potential impacts of browse quality and rainfall on different reproductive parameters. This study contributes to our understanding of black rhinoceros population dynamics and enhances our ability to manage the population in Namibia.