Rhinoceros horns have become shorter over the last century, the development could be a result of hunters and poachers targeting larger prizes. Rhino horns were much sought after among hunters over the centuries, while modern poachers sell them for use in traditional medicines in China and Vietnam.
“In the case of rhinos, people basically have always wanted the largest horn,”
Said Oscar Wilson, a doctoral student and first author of the research at the University of Helsinki.
Wilson and colleagues say a study of archive images of the animals suggests the size of a rhino’s horn, relative to its body length, has decreased over time. A similar trend has been recorded for creatures such as elephants and wild sheep.
“Preferential hunting selection for individuals with larger horns or tusks resulted in individuals with smaller features surviving and reproducing more, passing on these traits to future generations, and resulting in an evolutionary change,”
the researchers write in the journal People and Nature.
They made their discovery by examining artwork and photographs of rhinos held by the Rhino Resource Center in Utrecht. Some of the art dates back to the 15th century.
The team focused on 80 photographs of rhinos that show the creatures side on. They calculated the length of the horn relative to that of the animal’s body before taking an average of these values and calculating the difference compared with the ratio seen for each particular image. As a result, the team were able to explore whether the relative size of rhino horns got larger or smaller over time with respect to the average ratio.
Relative to their body length, black and white rhinos had the longest horns, while Sumatran rhinos had the shortest. However, for all five species of rhino, the relative length of the horn has decreased over time.
While 65 of the rhinos photographed were in captivity, Wilson noted that the majority came either directly from the wild, or were born to rhinos who had previously lived in the wild. he suggests the decrease in horn length likely reflects selection pressures that the animals face in their natural habitat, although the researchers are now carrying out further work with wild populations to explore whether the same trend is seen.
“Rhinos use their horns, so losing them [is] probably not going to be good for them,”
Wilson said.
