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Historical photos suggest that rhino horns have gotten smaller

People have always been fascinated by rhinos, finding them charismatic and impressive. These great mammals are depicted in historical and contemporary artworks and photographs for many different reasons and researchers have begun to appreciate the potential of these images as a rich source of data. This is particularly salient as numbers of rhinos of all species decrease and research on living specimens becomes more and more difficult. 

In a recent study, researchers from the University of Helsinki, University of Cambridge and the Rhino Resource Center (RRC) in the Netherlands undertook an analysis of 1,531 pieces of artwork and 1,627 photographs depicting rhinos, all of which are held in an online repository by the RRC. Their aim was to investigate the ways in which depictions of human interactions with rhinos have changed over time. In addition, they used a sample of 80 profile photographs of rhinos to determine whether morphological data on horn lengths, extracted from photographs, indicate any change in this feature over time. 

In the archives of the RRC, the researchers found digital records of artworks dating back over the past 500 years, and of photographs from the last 150 years. They assigned these to broad categories that represented different relationships between society and rhinos; for example, hunting, conservation, natural history and captivity. Categories were further grouped as consumptive or non-consumptive. Consumptive relationships involved the death of rhinos or their removal from the natural habitat (e.g., hunting, curiosity, museum, captivity, dominion, poaching and circus), whereas non-consumptive relationships did not kill or remove rhinos from their habitat (e.g., conservation, caretaking, education, academic, cartoons).

Although all five extant species of rhinos are represented in the RRC’s data set, the researchers found that earlier images more commonly show Indian rhinos (Rhinoceros unicornis) whereas the two African species (white rhino Ceratotherium simum, and black rhino Diceros bicornis) feature more prominently in recent images. Images of Javan (Rhinoceros sondaicus) and Sumatran (Dicerorhinus sumatrensis) rhinos are uncommon throughout the data set.

The results of the study, published in the journal People and Nature, showed a clear change in how rhinos are portrayed. Hunting scenes in both artwork and photos were more common prior to 1950, but conservation became more common after this date. Depictions of rhino natural history and rhinos in captivity also became more common in artwork from the late 1700s onwards, and in photos from the 2000s onwards. Furthermore, the researchers found that the proportion of images featuring non-consumptive uses of rhinos increased over time, although in this case from the turn of the 19th century. 

Many hundreds of photographs showing rhinos shot dead by hunters, taken in the late 19th and early 20th centuries, are present in the collection. These include a photograph of American President Theodore Roosevelt, taken in 1911, standing triumphantly over a black rhino he had just killed. Other early images show rhinos as huge, frightening animals chasing humans. The researchers think these images helped justify the hunting of these animals.

The experts also propose that peak times of hunting activities coincided with European colonial expansion into regions where rhinos occurred and that, once colonial powers pulled out of these regions and they achieved independence, European hunters no longer had easy access for hunting. The researchers suggest that the number of hunting images for a given species is likely to be associated with the true levels of hunting, particularly in the 19th and early 20th centuries, and to be correlated with the reported declines in rhino numbers during this time.

“We found that we can use images from the last few centuries to visualize how human attitudes towards wildlife have changed, and how artists have influenced these views,” said Dr. Ed Turner at the University of Cambridge’s Department of Zoology, senior author of the report.

The images suggest that there was very little effort to promote rhino conservation to the public before the 1950s. But after this the focus suddenly changed from hunting the animals to trying to keep them alive. The most recent images appear to reflect a growing awareness of the threats facing the natural world in general.

“For at least a few decades now there’s been much more of a focus on the conservation of rhinos – and this is reflected in the more recent images, which relate to their conservation in sanctuaries or their plight in the wild,” said study first author Oscar Wilson, who is now based at the University of Helsinki, Finland. 

The 80 photographs of individual rhinos used to assess changes in horn length represented all five of the extant rhino species. Morphological measurements of body and horn dimensions were made so that horn length could be accurately related to overall body size. This was important as the photos did not have any measure of scale. Analysis of the results showed that, across all species, the horn length increased with body size, and the relative length of the horn to body length decreased slightly, but significantly over time.  

The researchers think rhino horns have become smaller due to intensive hunting. Whether this has been for trophies or to supply material for medicines or traditional carvings in certain eastern and middle-eastern countries, the rhinos with the largest horns are invariably the targets. This leaves smaller-horned individuals to breed and pass on their genes for smaller horns to future generations. According to the researchers, these results could be indicative of directional selection in response to hunting pressures, as has been noted in obvious features such as horns and tusks in other groups of animals.

“We were really excited that we could find evidence from photographs that rhino horns have become shorter over time. They’re probably one of the hardest things to work on in natural history because of the security concerns,” said Wilson. “Rhinos evolved their horns for a reason – different species use them in different ways such as helping to grasp food or to defend against predators – so we think that having smaller horns will be detrimental to their survival.”

“Taken together, our results demonstrate the potential and scope for using online images to study the changing relationship between people and the natural world, and long-term morphological changes in species,” concluded the study authors. “We advocate a greater use of these data, and the development of more image repositories such as the RRC, to bring data together in an easily accessible format with associated detailed information.”

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By Alison Bosman, Staff Writer

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