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New research: The cost of species extinction – Evidence from the collapse of vultures in India

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New research: The cost of species extinction – Evidence from the collapse of vultures in India

A new paper from Dr Anant SudarshanLink opens in a new window, co-authored with Dr Eyal Frank of the University of Chicago, studies the impact on human well-being of the sudden collapse of vultures in India and makes an important contribution to our understanding of the cost of biodiversity losses.

Vultures have evolved as highly efficient scavengers and play an important sanitation and public heath role in India. By eating livestock carcasses, vultures remove the remains from the environment, preventing the bodies from rotting in the open air and potentially transmitting pathogens to other scavengers or allowing them to enter the water supply.

The highly effective scavenging of vultures – able to reduce a cow to bones within 40 minutes – also limits the numbers of non-vulture scavengers such as dogs and rats that can transmit diseases to humans by leaving them little or nothing to eat.

In the mid 1990s, vulture populations fell dramatically – the fastest collapse of a bird species in recorded history. The cause of death was initially mysterious. It was not until a decade later, in 2004, that a paper in Nature traced the near extinction of these birds to a chemical called diclofenac.

Diclofenac is a common painkiller that has been prescribed to people since the 1970s. But the expiry of a long-standing patent and the development of generics in 1993, made it cheap enough for farmers in India to use it to treat livestock as well. Unfortunately, this medicine – safe for human beings and for cattle – turned out to be fatal to vultures. A bird that ate a carcass from an animal that had been given diclofenac would likely die within weeks.

Comparing data from before and after the widescale adoption of diclofenac by farmers, the researchers find that death rates increased by more than 4 per cent after the near-extinction of vultures in areas where they had previously thrived – an increase of close to 0.5 additional deaths per 1,000 people. To put this in context, that increase is about 4 times as large as the 2021 mortality rate in England and Wales.

The cause of these additional deaths was an increase in animal carcasses that were no longer being picked clean by vultures, creating a significant public health risk. This may have led to an increase in dog and rat populations, in turn spreading infectious diseases and rabies. Carcasses disposed in water bodies may also increase water pollution and spread pathogens.

By increasing understanding of the social costs of keystone species collapse, the research will help inform policy decisions on investment into species conservation and rehabilitation.

Dr Sudarshan said: “The vulture collapse in India is a particularly stark example of what can happen when new chemicals are introduced into a fragile and diverse ecosystem – and our findings show that consequences are not confined only to the species that is directly affected.

“Although it is generally agreed that biodiversity loss is damaging, there is very little evidence of the effect of specific species loss on human well-being, and a particularly large knowledge gap around the social costs of the loss of keystone species like vultures.

“Our evidence on the public health implications of the decline of vulture species in India will help inform current vulture recovery work in India, and global conservation policies more broadly. More generally this type of work underscores the importance of carefully targeting conservation efforts”