>
Rhino horns have shrunk over the past century because of hunting by humans, suggest scientists.
Decades of shooting rhinos with the longest horns means that only smaller-horned survivors remain and these animals are now passing on their genes.
The findings by Cambridge University experts, published in the journal People And Nature, are based on an analysis of photos of the animals from the past 140 years, including all five species of rhino: white, black, Indian, Javan and Sumatran.
Rhino horns have shrunk over the past century because of hunting by humans, suggest scientists. Pictured: a Sumatran rhino at Port Lympne Safari Park in 1986
Decades of shooting rhinos with the longest horns means that only smaller-horned survivors remain and these animals are now passing on their genes. Pictured: a drawing of a white rhino from 1984
The researchers said working with photographs got round the problem of working with physical rhino horn specimens – which researchers are typically not allowed to access due to security concerns.
Oscar Wilson, formerly a researcher in the University of Cambridge’s department of zoology, who is first author of the report, said: ‘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.’
The findings by Cambridge University experts, published in the journal People And Nature, are based on an analysis of photos of the animals from the past 140 years, including all five species of rhino: white, black, Indian, Javan and Sumatran. Pictured: Indian rhino mother and calf on display in Whipsnade Zoo, ZSL in 2021
The researchers said working with photographs got round the problem of working with physical rhino horn specimens – which researchers are typically not allowed to access due to security concerns. Pictured: Theodore Roosevelt standing above a black rhino he has just killed in 1911
Mr Wilson, who is now based at the University of Helsinki in Finland, added: ‘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.’
The researchers measured the horns of 80 rhinos, photographed between 1886 and 2018 with their horns in full view.
The photographs – found in the online repository The Rhino Resource Centre – include all five species of rhino: white, black, Indian, Javan and Sumatran.
They looked at images of rhinos shot dead by hunters, including one showing former US President Theodore Roosevelt, taken in 1911, standing over a black rhino he had just killed.
The researchers measured the horns of 80 rhinos, photographed between 1886 and 2018 with their horns in full view. Pictured: Sumatran rhino in Rangoon, 1913
Mr Wilson, who is now based at the University of Helsinki in Finland, added: ‘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.’ Pictured: Woodcut of the Lisbon Rhinoceros by Albrecht Düre dating back to 1515
The researchers also measured other rhino body parts so the horn length could be accurately measured in proportion to body size.
The team considered rhino artwork covering a span of more than 500 years – when drawings were used to keep records of species.
The images and artwork show that until the 1950s, there was very little effort to promote rhino conservation to the public.
Sumatran rhino called Tam in 2011, who was housed in Tabin Wildlife Reserve, Sabah, Borneo as part of a project run by the Borneo Rhino Alliance
Pictured: Clara, the celebrity touring Indian rhino in the 18th Century.
Mr Wilson said: ‘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.’
Rhinoceros are endangered species with fewer than 30,000 living in the wild today.
At the start of the 20th century, there were more than 500,000.
Three species of rhino – black, Javan and Sumatran – are classed as critically endangered.