South Asian vultures started dying in huge numbers in the 1990s but no one knew why. They were on the verge of extinction before scientists worked out what was killing them. Bob Howard has been hearing from Munir Virani of the Peregrine Fund, who discovered that the vultures’ livers were being damaged when they fed on the carcasses of cattle which had been treated with a widely-used painkiller.

White-backed vultures in their enclosure at the Vulture Conservation Centre run by World Wide Fund for Nature-Pakistan (WWF-P) in Changa Manga. September 20, 2017. Credit: ARIF ALI/AFP via Getty Images