The black rhinoceros is a large mammal, classified as "critically endangered" by the IUCN (International Union for Conservation of Nature). There are just 5,500 individuals left in the world, living rather hidden lives. The main cause of mortality is poaching for its horns, which are sold on the black market for more than gold.
To deal with this, the managers of some nature reserves have opted for preventive dehorning of the animals, an operation carried out here in conditions that respect the animal (see box). But what are the consequences? Answering this question is one of the objectives of a team of ecology and conservation researchers and practitioners.
Dehorning does not increase natural mortality or affect the animal’s ability to survive," notes Vanessa Duthé, PhD student at UniNE’s Functional Ecology Laboratory. However, the absence of horns results in an average 45.5% reduction in territory. At first sight, this finding implies a change in the spatial use of resources as well as in the structuring of dominance, and it will also undoubtedly be more difficult to select individuals for relocation in order to optimize the management of metapopulations.
’ On the other hand, notes the researcher, smaller territories may generate less fighting between males, which can be deadly, since we found that dehorned rhinos are on average 37% less likely to engage in social interactions than individuals with horns. ’
These results are based on observations of 368 individuals from different populations in South Africa, carried out over 15 years. This is a collaboration between 10 different reserves. Managers, ecologists and monitoring officers are among the co-authors of the study," continues the project initiator. As a result, we have gathered unique and very rare data that has enabled us to detect a particular behavior in response to dehorning. ’
However, Vanessa Duthé and her colleagues cannot yet say whether dehorning is really positive or negative, as the animal’s long life cycle (30 to 50 years) requires longer-term data to be taken into account to conclude on the effects on reproduction and genetics. Another study carried out in Namibia, however, showed that dehorning had no impact on the reproductive rate, suggesting instead that, in conjunction with other measures, it has an overall effect in terms of improving the preservation of the black rhinoceros.
What is dehorning?Dehorning is not a painful operation. The rhinos are sedated, blindfolded and fitted with earplugs to limit sensory stress. The innervated part of the horn is then cut off, catalogued and stored in a safe place. The procedure is carried out by a team of experienced veterinarians and specialists. Horns are made of keratin and grow back, just like fingernails. If we’ve come to this point, it’s because of the urgency of the situation," warns Vanessa Duthé. For, despite a certain decline, poaching is still very intensive. Faced with the daily loss of rhinos, many reserve managers have decided to dehorn to deter poachers, in order to protect black rhinos from a terrible death.
Vanessa Duthé et al. Reductions in home-range size and social interactions among dehorned black rhinoceroses (Diceros bicornis), Proc. Natl. Acad. Sci. U. S. A, (2023)