Photos show that rhino horns have gotten smaller over the past 100 years, probably because of hunting

rhino horns have gotten smaller over the past 100 years; two rhinoceros walking on brown field
Photo by Nicole Kruger on

Photos show that rhino horns have gotten smaller over the past 100 years, probably because of hunting

Researchers at the University of Cambridge have made the first measurements to show that rhinoceros horns have been getting smaller over time. They did this by looking at photos from the last 100 years.

Researchers looked at photos of 80 rhinos taken from the side between 1886 and 2018. They then measured the length of the horns. The Rhino Resource Center, which is an online library, has photos of all five species of rhino: the white, the black, the Indian, the Javan, and the Sumatran. Over the last 100 years, it was found that the length of horns in all species has decreased by a lot.


Real rhino horns are so valuable that researchers usually can’t get to them to study them. This is the first time that horn length has been measured over a long period of time because of strict security rules.

Researchers think that because rhinos have been hunted so much, their horns have shrunk over time. Rhino horns sell for a lot of money and are in high demand in China and Vietnam, where they are used in traditional medicines. People and Nature, a magazine, is putting out the report today.

The number of rhinos has dropped by a lot because of hunting, and researchers think that killing the rhinos with the longest horns has left more rhinos with shorter horns. These rhinos have had more babies and passed on their smaller horns to the next generation. This has been shown before for some other animals, but never for rhinos.


A mother and her baby Indian rhino at Whipsnade Zoo in the UK. Credit: Oscar Wilson
We were really happy to find evidence in photographs that rhino horns have gotten shorter over time. They’re probably one of the hardest things to study in natural history because of security concerns, said Oscar Wilson, the first author of the report and a former researcher at the University of Cambridge’s Department of Zoology. Wilson now works at the University of Helsinki in Finland.

He also said, “Rhinos developed their horns for a reason. Different species use them in different ways, like to grab food or protect themselves from predators, so we think that making their horns smaller will hurt their chances of survival.”

Researchers also measured other parts of each rhino’s body, like the length of its body and head, so that the length of its horn could be accurately measured in relation to its body size. By looking at thousands of drawings and photos made over the last 500 years, they also saw a big change in how people thought about rhinos around 1950, when people started trying to protect them instead of hunting them.


Theodore Roosevelt stands over a black rhino he just killed (1911). Credit: Free to Use
“We found that we can use pictures from the last few hundred years to see how people’s views on wildlife have changed and how artists have influenced these views,” said Dr. Ed Turner, who is the senior author of the report and works at the University’s Department of Zoology.

There are many hundreds of photos from the late 19th century and early 20th century that show dead rhinos that hunters shot. One of these is a picture from 1911 of American President Theodore Roosevelt standing proudly over a black rhinoceros that he had just killed.

Other early pictures show rhinos as big, scary animals that chase people. The researchers think that these pictures helped explain why these animals were shot.


Before the 1950s, the pictures show that not much was done to get people interested in rhino conservation. But after this, the focus suddenly shifted from hunting the animals to trying to keep them alive. The researchers say that this change happened at the same time that European empires fell apart. When African countries became independent, it was harder for European hunters to go to Africa to hunt.

More recent pictures seem to show that people are becoming more aware of the dangers facing the natural world.

“Rhino conservation has gotten a lot more attention in the last few decades,” said Wilson. “This is reflected in the more recent images, which show rhinos in sanctuaries or in trouble in the wild.”


The Rhino Resource Center has more than 5,000 pictures and photos of rhinos. These came from a lot of research in archives and from rhino experts who sent them in. The art goes back more than 500 years, and the photos go back 150 years.


Image-based analyses from an online repository provide rich information on long-term changes in morphology and human perceptions of rhinos, People and Nature (2022). DOI: 10.1002/pan3.10406

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