Cutting off rhino horns to prevent poaching makes them homebodies | Science

When rhino poaching reached a crisis level in 2014, wildlife managers in southern Africa turned to a last-ditch defense. They started sawing off horns, which doesn’t hurt rhinos, but may dissuade poachers from killing the endangered animals. Now, researchers have for the first time shown that this conservation practice changes the behavior of black rhinoceros (Diceros bicornis), making the animals roam far less widely and presumably interact less with other rhinos.

The discovery, reported today in the Proceedings of the National Academy of Sciences, raises important questions, says Michael Knight, chair of the International Union for Conservation of Nature’s African Rhino Specialist Group, who was not involved with the study. “Maybe we’re impacting the social fabric. Is that going to impact the potential that a population can breed as well as they [could] before?” And Wayne Linklater, a wildlife ecologist at California State University, Sacramento, worries that the shyness of dehorned rhinos might ultimately make managed populations less wild.

The black rhino, which lives only in Africa, is critically endangered. Only about 6200 remain in the wild, mainly in South Africa, Namibia, Zimbabwe, and Kenya. Although the population overall is growing slowly, poaching holds back the species’ recovery. White rhinos (Ceratotherium simum), also limited to Africa, are more common—with a total population of about 22,100—but are still categorized as near-threatened because of poaching. Rhino horn is used in traditional Chinese medicine, is a sign of wealth in Southeast Asia, and can fetch up to $65,000 per kilogram on the black market.

Wildlife managers first started to dehorn rhinos in Namibia in 1989. The process of sedating and capturing a rhino is complex and risky. Sometimes a helicopter is used to herd a lone rhino toward a relatively safe patch of ground, where it can run without injuring itself or falling off a cliff, for example. Then a veterinarian shoots a tranquilizer dart from the helicopter, and the team follows the animal for several minutes until it gets too drowsy to run. The team then blindfolds the animal and gives it earplugs, to lessen stress from the sound of the chainsaw.

Rhino horn is made of keratin, like fingernails, so most of it can be cut off without any bleeding or pain. There are still risks to the rhino and workers, however, which makes the practice controversial. It’s also expensive, costing hundreds of dollars per animal, and the horn regrows, so managers often have to repeat the process every 18 to 24 months. After poaching declined, Namibia ceased dehorning rhinos from 1995 to 2014, but since then game reserves and parks return to the practice when poaching worsens. Whether dehorning prevents poaching, or just displaces it, isn’t clear; scientific studies have been inconclusive.

Researchers have also wondered about the effects of dehorning on rhinos’ social interactions. Vanessa Duthé, a Ph.D. student in conservation biology at the University of Neuchâtel, reasoned that because male rhinos will fight with their horns to defend their territory from other males, dehorning might affect the size of their turf. The behavior of female rhinos might also change, she suspected, because they use their horns to defend themselves and their calves from predators or harassment from male rhinos.

So Duthé started to map the territories of the black rhinos at Manyoni Private Game Reserve in South Africa based on records of sightings before dehorning began there in 2016. (Individual rhinos are identified by unique notches that game managers cut into their ears.) Then she repeated the mapping after the horns were cut off. Some of the dehorned rhinos lost 80% of their territory, she found. “It was really, really obvious and highly significant.”

Then, Duthé expanded the study to include data from nine other game reserves in South Africa, creating a large data set of more than 15 years of observations. By law, game reserves must keep tabs on rhinos, and wardens regularly record the identity and location when they see the animals. Working with more than 24,000 sightings or 368 rhinos, Duthé and colleagues found that when rhinos were dehorned, their territory shrank on average by nearly 12 square kilometers or 45% of their previous range. The effect was more dramatic for females, who saw a 53% decrease in territory, compared with 38% for males.

Jeff Muntifering, a conservation biologist with the Minnesota Zoo Foundation and science adviser to the Save the Rhino Trust, is a bit surprised. “I would not have thought that removing horns would make such a striking difference in the ranging behaviors,” he says.

Further statistical analysis of the degree of overlap between adjacent territories showed that dehorned rhinos were 37% less likely to encounter another rhino than before. “We think it’s a confidence matter. They lose their main defense, so they feel vulnerable, and males avoid each other more,” Duthé says. Knight agrees: “Take your horn off, and my god you’ve lost your status.”

Duthé says the results may hold true for white rhinos, but they are by nature more gregarious than black rhinos, so the analysis might need to be modified.

Knight is intrigued by a possible consequence mentioned in the paper: Game reserves might be able to keep more rhinos if each one needs less territory. To Linklater, this raises the concern that dehorning might be inadvertently domesticating rhinos, because the rhinos that are most wild and can least acclimate to capture would be least likely to survive and breed. “Are we farming rhino or are we protecting wild populations? It raises all sorts of issues about what we’re protecting here.”

One of the most important remaining questions is whether dehorning makes a rhino less likely to breed than one with intact horns, Knight says. That will likely take at least 5 years to determine, he says. If it does, Linklaters ays, that would be another reason to limit the use of dehorning to emergencies of intense poaching.

When rhino poaching reached a crisis level in 2014, wildlife managers in southern Africa turned to a last-ditch defense. They started sawing off horns, which doesn’t hurt rhinos, but may dissuade poachers from killing the endangered animals. Now, researchers have for the first time shown that this conservation practice changes the behavior of black rhinoceros (Diceros bicornis), making the animals roam far less widely and presumably interact less with other rhinos.

The discovery, reported today in the Proceedings of the National Academy of Sciences, raises important questions, says Michael Knight, chair of the International Union for Conservation of Nature’s African Rhino Specialist Group, who was not involved with the study. “Maybe we’re impacting the social fabric. Is that going to impact the potential that a population can breed as well as they [could] before?” And Wayne Linklater, a wildlife ecologist at California State University, Sacramento, worries that the shyness of dehorned rhinos might ultimately make managed populations less wild.

The black rhino, which lives only in Africa, is critically endangered. Only about 6200 remain in the wild, mainly in South Africa, Namibia, Zimbabwe, and Kenya. Although the population overall is growing slowly, poaching holds back the species’ recovery. White rhinos (Ceratotherium simum), also limited to Africa, are more common—with a total population of about 22,100—but are still categorized as near-threatened because of poaching. Rhino horn is used in traditional Chinese medicine, is a sign of wealth in Southeast Asia, and can fetch up to $65,000 per kilogram on the black market.

Wildlife managers first started to dehorn rhinos in Namibia in 1989. The process of sedating and capturing a rhino is complex and risky. Sometimes a helicopter is used to herd a lone rhino toward a relatively safe patch of ground, where it can run without injuring itself or falling off a cliff, for example. Then a veterinarian shoots a tranquilizer dart from the helicopter, and the team follows the animal for several minutes until it gets too drowsy to run. The team then blindfolds the animal and gives it earplugs, to lessen stress from the sound of the chainsaw.

Rhino horn is made of keratin, like fingernails, so most of it can be cut off without any bleeding or pain. There are still risks to the rhino and workers, however, which makes the practice controversial. It’s also expensive, costing hundreds of dollars per animal, and the horn regrows, so managers often have to repeat the process every 18 to 24 months. After poaching declined, Namibia ceased dehorning rhinos from 1995 to 2014, but since then game reserves and parks return to the practice when poaching worsens. Whether dehorning prevents poaching, or just displaces it, isn’t clear; scientific studies have been inconclusive.

Researchers have also wondered about the effects of dehorning on rhinos’ social interactions. Vanessa Duthé, a Ph.D. student in conservation biology at the University of Neuchâtel, reasoned that because male rhinos will fight with their horns to defend their territory from other males, dehorning might affect the size of their turf. The behavior of female rhinos might also change, she suspected, because they use their horns to defend themselves and their calves from predators or harassment from male rhinos.

So Duthé started to map the territories of the black rhinos at Manyoni Private Game Reserve in South Africa based on records of sightings before dehorning began there in 2016. (Individual rhinos are identified by unique notches that game managers cut into their ears.) Then she repeated the mapping after the horns were cut off. Some of the dehorned rhinos lost 80% of their territory, she found. “It was really, really obvious and highly significant.”

Then, Duthé expanded the study to include data from nine other game reserves in South Africa, creating a large data set of more than 15 years of observations. By law, game reserves must keep tabs on rhinos, and wardens regularly record the identity and location when they see the animals. Working with more than 24,000 sightings or 368 rhinos, Duthé and colleagues found that when rhinos were dehorned, their territory shrank on average by nearly 12 square kilometers or 45% of their previous range. The effect was more dramatic for females, who saw a 53% decrease in territory, compared with 38% for males.

Jeff Muntifering, a conservation biologist with the Minnesota Zoo Foundation and science adviser to the Save the Rhino Trust, is a bit surprised. “I would not have thought that removing horns would make such a striking difference in the ranging behaviors,” he says.

Further statistical analysis of the degree of overlap between adjacent territories showed that dehorned rhinos were 37% less likely to encounter another rhino than before. “We think it’s a confidence matter. They lose their main defense, so they feel vulnerable, and males avoid each other more,” Duthé says. Knight agrees: “Take your horn off, and my god you’ve lost your status.”

Duthé says the results may hold true for white rhinos, but they are by nature more gregarious than black rhinos, so the analysis might need to be modified.

Knight is intrigued by a possible consequence mentioned in the paper: Game reserves might be able to keep more rhinos if each one needs less territory. To Linklater, this raises the concern that dehorning might be inadvertently domesticating rhinos, because the rhinos that are most wild and can least acclimate to capture would be least likely to survive and breed. “Are we farming rhino or are we protecting wild populations? It raises all sorts of issues about what we’re protecting here.”

One of the most important remaining questions is whether dehorning makes a rhino less likely to breed than one with intact horns, Knight says. That will likely take at least 5 years to determine, he says. If it does, Linklaters ays, that would be another reason to limit the use of dehorning to emergencies of intense poaching.