Preventive ‘dehorning’ of black rhinos to prevent poaching leads to fewer rhino victims, but also has a downside. In PNAS write Swiss and South African researchers that the behavior of the rhinos clearly changes: they engage in fewer social interactions (including fights with conspecifics). Their territory is also shrinking. This may have long-term consequences for rhino populations – although it is not yet clear in what way and to what extent.
The black rhinoceros (Diceros bicornis) is critically endangered: since the 1960s, numbers have already declined by about 98 percent due to poaching. Today it is estimated that some 5,000 individuals remain. Rhinoceros horns are believed to have medicinal powers in Southeast Asia, and one kilogram of them is believed to have healing powers PNASitem could fetch about $65,000—more than the same weight in gold or diamonds.
Because rhinos are killed by poachers to get their horns, conservationists are increasingly taking preventative measures. They remove the horn in an animal-friendly way, so that the rhinoceros lives. But until now little was known about possible consequences of this.
Better security
The current study was conducted among 368 black rhinoceroses in 10 South African wildlife sanctuaries over a 15-year period. In 2013, not a single individual had been dehorned preventively, but in 2020 this will already be two thirds of all animals. The number of rhinos killed by poachers has declined over the past decade, although the researchers say there is no definite causal relationship to the dehornings; the security of nature reserves, for example, also increased. The number of natural deaths has remained virtually the same.
Nevertheless, an effect of removing the horn can be observed, the biologists write. After the procedure, male black rhinos in particular engage in 37 percent fewer social interactions with conspecifics and other large herbivores. This way they are less likely to seek confrontation – not surprising, because the horn is used in territorial battles. Also, the area in which they operate – their homerange – by more than 45 percent, to just under 12 square kilometers.
What are the consequences of those smaller ones home ranges is still unclear. For example, a smaller habitat could result in less food availability, but on the other hand, more habitats could be created within a reserve, allowing the population to expand. At the same time, a decrease in social interactions may also affect hierarchical relationships between individuals, and possibly even reproductive success. Long-term monitoring is necessary, the researchers emphasize, to see what and how much influence dehorning will ultimately have on population size.