Rhino Horns Have Become Smaller Due To Continuous Hunting, Analysis Of Photos Shows
Researchers from University of Cambridge have scrutinised over a century's worth of photos, and made the first ever measurements that show rhinoceros horns have gradually decreased in size over time.
Rhinos, which once roamed many places throughout the world, have dwindled in numbers over the years, so much so that only 27,000 rhinos remain in the wild. Three rhino species, namely Black, Javan and Sumatran, are critically endangered. Assam is home to the largest population of greater one-horned rhinos, or the Indian rhinoceros, with more than 90 per cent in Kaziranga National Park. The Indian rhinoceros is listed as 'vulnerable' on the International Union for Conservation of Nature (IUCN) Red List.
With the help of successful conservation efforts, the population of greater one-horned rhinos has increased from around 200 at the beginning of the 20th century to around 3,700 today. Also, the status of the greater one-horned rhinos has improved from endangered to vulnerable due to a significant rise in population. However, the greater one-horned rhinos are still under threat due to habitat loss, degradation, and poaching for its horn.
Gradual decrease in the size of rhino horns
An analysis of photographs has suggested that rhino horns have become smaller due to continuous hunting.
Researchers from University of Cambridge have scrutinised over a century's worth of photos, and made the first ever measurements that show rhinoceros horns have gradually decreased in size over time.
The report stating the findings was published November 1 in the journal People and Nature.
Photographs of rhinos captured between 1886 and 2018 analysed
The horns of 80 rhinos, photographed in profile view between 1886 and 2018, were measured. The photos are held by the Rhino Resource Centre, an online repository. The pictures include all five species of rhino: white, black, Indian, Javan and Sumatran. Over the last century, horn length was found to have decreased significantly in all species.
Due to strict security protocols, researchers cannot find real rhino horns, which are extremely valuable. The new analysis makes the first time that horn length has been measured over a long time frame.
Rhino horns have decreased in size over time due to intensive hunting, the researchers believe. Rhino horns are in demand both as a financial investment, and for their use in traditional medicines in China and Vietnam.
How hunting leads to smaller rhino horns over time
Due to hunting, there have been severe declines in rhino populations. Shooting rhinos with the longest horns has increasingly left smaller-horned survivors, the researchers suggest. These rhinos have reproduced more and passed on their smaller traits to future generations. This was shown for other animals before, but never rhinos.
Why are short rhino horns detrimental to the survival of the animals?
In a statement released by University of Cambridge, Oscar Wilson, first author on the report, said the researchers were really excited that they could find evidence from photographs that rhino horns have become shorter over time. He added that rhinos are probably one of the hardest things to work on in natural history because of the security concerns.
Wilson also said that rhinos evolved their horns because different species use them in different ways such as helping to grasp food or to defend against predators. Therefore, having smaller horns will be detrimental to their survival.
What other parameters did the team measure?
The other parameters which researchers measured on each rhino photograph included body and head length. They made these measurements so that horn length could be accurately measured in proportion to body size.
Why human perceptions of rhinos changed around the 1950s
The researchers analysed thousands of drawings and photographs made over the last 500 years, and observed a dramatic shift in human perceptions of rhinos around 1950. This was the time when the animals became the focus of conservation efforts.
Dr Ed Turner, senior author on the report, said the researchers found that they can use images from the last few centuries to visualise how human attitudes towards wildlife have changed, and how artists have influenced these views. Of the many hundreds of photographs showing rhinos shot dead by hunters, taken in the late 19th and early 20th century, is a photograph of the then American President Theodore Roosevelt, captured in 1911. Roosevelt can be seen standing triumphantly over a black rhino he had just killed.
How were rhinos portrayed in early images?
In other early images, rhinos were shown as huge, frightening animals chasing humans. These images may have helped justify the hunting of these animals, researchers believe.
There was very little effort to promote rhino conservation to the public before the 1950s, the images suggest. However, after the 1950s, the focus suddenly changed from hunting the animals to trying to keep them alive.
What do recent images of rhinos suggest?
This shift coincides with the collapse of European empires, the researchers say. During the collapse of European empires, African countries became independent and European hunters no longer had easy access to Africa for hunting.
The more recent images reflect a growing sense of awareness of the threats facing the natural world.
Wilson said for at least a few decades now, there has been much more of a focus on the conservation of rhinos, and this is reflected in the more recent images. The recent images relate to the conservation of rhinos in sanctuaries or their plight in the wild.
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