How Dehorning Affects Black Rhino Populations
Poaching and black-market demands are serious problems for the long-term survival of many endangered species. Rhinoceros (rhinos) are no exception — their parts and derivatives comprised nearly 12% of all illegal wildlife seizures (by value) between 2014 and 2018, behind only elephants and pangolins.
Rhino horns are among the most sought-after parts of rhinos on the black market. The horns are seen as status symbols and traditional medical treatments, despite a lack of any evidence of clinical benefits. In efforts to preserve individuals and the species as a whole, several anti-poaching programs have relied on “dehorning,” or the removal of most of a rhino’s horn. Theoretically, this decreases the value of the horn remaining, thus deterring would-be poachers.
According to the authors, there are existing concerns about the potential effects of dehorning on rhino behavior and biology, with mixed evidence both for and against it. To date, however, the bulk of dehorning research has focused on white rhino populations. In this study, researchers explore a number of possible long-term effects of dehorning on black rhinos in Namibia. Black rhinos are critically endangered, thus knowing whether their population dynamics are impacted by dehorning is vital to their survival.
To carry out the study, the researchers looked at four groups of rhinos, three of which had been dehorned to varying degrees and one that had never experienced dehorning. The team looked at several outcomes: age at first reproduction, inter-calving interval (the number of months in between births), birth sex ratios (the ratio of male to female calves born), calf survival (whether calves survived to become independent), cause of death, and lifespan. Overall, their dataset included 265 rhinos, 77 of whom had been dehorned at least once at some point. Population A had data going back to 1973, Population B to 2000, Population C to 1996, and Population D to 2008. Across the groups A, C, and D, respectively, about 37%, 50%, and 80% of all individuals had been dehorned.
The results for population productivity were encouraging. The authors report no significant differences in any of the studied outcomes between dehorned and horned rhinos. Importantly, the authors note that they couldn’t formally test for differences in age at first reproduction, as none of the dehorned sub-adult females had given birth to their first calf when the study was undertaken. Thus, this could be an important question to study for future researchers. For the other variables, however, dehorning did not seem to have a negative effect on the rhinos as individuals or at the population level.
While these results are promising, the authors also found no significant difference in the poaching of dehorned versus horned rhinos. While they acknowledge it could simply be that dehorning is ineffective in preventing poaching, they urge caution in this line of thinking. Prior research shows that without other anti-poaching strategies, dehorning on its own isn’t enough to prevent poaching. Moreover, dehorning usually takes place in areas with historically high poaching. Therefore, individuals living in these populations may already be at higher risk of poaching due to other factors (for example, proximity to roads and international borders). Similarly, more research is needed in this area to better understand the effects of dehorning on poaching.
For animal advocates, this research suggests that we don’t need to trade animal welfare for population management and poaching deterrence. Although the idea of dehorning may strike some advocates as wrong and harmful in itself, if the rhinos suffer no serious consequences, it may be a worthwhile strategy to preserve their long-term survival. It’s also possible that similar approaches may work for the protection of other endangered species. In conclusion, then, we can be cautiously optimistic about the use of dehorning to protect black rhinos, with the understanding that more research in this area is needed.