Curious collage shows rhino horns are shrinking due to the impact of hunting

Scientists analysed artwork and photographs to assess changes in horn length and human attitudes towards the animal

Published - November 03, 2022 05:38 am IST - GUWAHATI

A Rhinoceros with its calf grazes in the Pobitora wildlife sanctuary on the outskirts of Guwahati on October 11, 2022.

A Rhinoceros with its calf grazes in the Pobitora wildlife sanctuary on the outskirts of Guwahati on October 11, 2022. | Photo Credit: AP


The horns of rhinoceroses may have become smaller over time due to the impact of hunting, according to a recent study which used an interesting research approach—analysing artwork and photographs of the animal spanning more than five centuries.

The study, published in the latest edition of People and Nature by the British Ecological Society, relied on a repository of images maintained by the Netherlands-based Rhino Research Center (RRC). 

“We found evidence for declining horn length over time across species, perhaps related to selective pressure of hunting, and indicating a utility for image-based approaches in understanding societal perceptions of large vertebrates and trait evolution,” said the study, authored by scientists from the Universities of Helsinki and Cambridge, as well as the RRC.

Rhinos have long been hunted for their horns, which are highly valued in some cultures. The five surviving rhino species are still threatened by habitat loss and hunting. The study found that the rate of decline in horn length was highest in the critically-endangered Sumatran rhino and lowest in the white rhino of Africa, which is the most commonly found species both in the wild and in captivity. This observation follows patterns seen in other animals, such as tusk size in elephants and horn length in wild sheep, which have been driven down by directional selection due to trophy hunting, the study said.

The RRC’s repository, curated by experts, holds a collection of more than 4,000 rhino images, including artistic portrayals from as early as 1481 as well as photographs, of which the earliest was taken in 1862.

The scientists used this repository for two separate research approaches. They studied 3,158 images to assess the changes in representations of rhinos and human interactions with the animal over the last 500 years. They also identified 80 images, including all five rhino species, to analyse changes in horn length over time, extracting morphological data from photographs. 

“We only included photographs where the animal was side-on to the camera to facilitate more accurate and repeatable measurements. We excluded photos of any individuals where the horn had been cut, as horn length varies substantially between rhino species and therefore is an important species-specific morphological trait,” said the study.

Rhinos have been featured in European art for half a millennia, providing a valuable source of information for the scientists. The Indian rhino featured more in early artwork, but the number of images of other species, particularly white rhinos, has increased since the mid-19th century. 

“During the age of European imperialism (between the 16th and 20th centuries), rhinos were commonly portrayed as hunting trophies, but since the mid-20th century, they have been increasingly portrayed in a conservation context, reflecting a change in emphasis from a more to less consumptive relationship between humans and rhinos,” the study said.

“Online image repositories can offer a freely accessible, information-rich and cost-effective alternative to museum collections for studying long-term changes in human interactions with nature and ecological and evolutionary change,” it added.

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