Rhinoceroses’ horns have decreased in size over centuries as a result of the animals with the longest horns being killed, leaving behind only short-horned rhinos, according to researchers with the University of Cambridge and Rhino Resource Centre.

  • Measurements of the horns of white, black, Indian, Javan, and Sumatran rhinoceroses, photographed in profile between 1886 and 2018, show that horn length has decreased significantly over the past century.

  • For centuries, hunters have targeted the rhinos with the longest horns, and this appears to have increasingly left smaller-horned survivors to reproduce and pass on their smaller traits to future generations.

  • Hundreds of photographs taken in the late 19th and early 20th century showing rhinos shot dead by hunters suggest that very little effort was made to promote rhino conservation to the public before the 1950s, when the focus suddenly changed from hunting the animals to trying to keep them alive.

  • In addition to being shot for trophies, rhinos are threatened by poaching, because their horns command a high price and are in demand as a financial investment and for their use in traditional medicines in China and Vietnam.

  • Different species of rhinos use their horns in different ways, such as helping to grasp food or to defend against predators, so having smaller horns could be detrimental to their survival.

This is a summary of the article, “Image-Based Analyses From an Online Repository Provide Rich Information on Long-term Changes in Morphology and Human Perceptions of Rhinos,” published by People and Nature on November 1, 2022. The full article can be found on besjournals.onlinelibrary.wiley.com.

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