Horn cutting reduces rhino deaths in Africa – 06/20/2023 – Science

Preemptively cutting rhino horns, a drastic measure to prevent the animals from being targeted by poachers, is linked to a decrease in pachyderm deaths — but it is also altering their behavior, with consequences that are difficult to predict, warns a new study.

The data come from a survey carried out with populations of black rhinos (bicornis diceros) living in ten reserves in South Africa. The work, coordinated by Vanessa Duthé, from the University of Neuchâtel (Switzerland), has just been published in the American scientific journal PNAS.

With a total population that today does not exceed 5,000 individuals, the black rhinos, like other species in their group, are at risk of extinction due to several factors, among which stands out the high value attributed to their horns in traditional medicine and other Southeast Asian cultural practices. It is estimated that 1 kg of rhino horn is worth around BRL 300,000 on the illegal market for products derived from biodiversity —more than gold or diamonds.

Given this, conservationists have adopted the preventive removal of horns, done after anesthetizing the animals in the wild, with the intention of taking out of the picture the economic incentive that hunters have to kill pachyderms. In the sites studied by Duthé and his colleagues in South Africa, for example, the proportion of rhinos whose horns were dehorned increased from 0% in 2013 to 63% in 2020.

To check whether the measure brought results from the point of view of conservation of the species, the researcher and her collaborators compiled data on 368 rhinos from these reserves, collected between 2005 and 2020, corresponding to more than 24,000 sightings of the animals.

The first conclusion is that both deaths caused by hunters and those linked to other factors, such as confrontations between members of the species, dropped after the “dehorning” campaigns began. Although hunting declined throughout South Africa during this period, the drop was most significant in territories where dehorning became popular.

It is still not possible to say that there is a cause and effect relationship, however, since the spread of the practice of sawing the horns coincided with the tightening of punishments for poachers, both in South Africa and in Zimbabwe, say the researchers. In any case, there is no evidence that horn loss increases the risk of mortality for mutilated animals.

The problem, for now, seems to be another one. As horns are important weapons for confrontations between males of the species and also with other large animals, such as elephants, everything indicates that their absence is leading black rhinos to retreat when faced with threats.

This is because, in the period after the introduction of “dehorning”, the territory occupied by each individual was, on average, 45% smaller. Additionally, hornless individuals had a 37% reduction in social interactions with other rhinos.

“Interactions between males are the most affected”, explained Duthé to Sheet. On the other hand, she says it’s not likely that females will end up choosing only horned males. “Overall, we didn’t see a change in population growth, and that didn’t show up in a study done in Namibia either,” she says.

“However, the reduction in interactions, due to the drop in exploratory behavior, can affect the reproductive success of individuals. Dominant males that used to have very large territories, with a lot of overlap with female territories, may now end up producing fewer offspring”, ponder. The exact effect can only be elucidated with more long-term monitoring, but initial data indicate that it is not possible to depend on dehorning as a magic solution to the problem of animal population decline.