Diclofenac and India’s Vultures: The Hidden Human Cost

A painkiller for cattle, introduced during the 1990s, triggered the unforeseen collapse of India’s vulture populations, which have yet to return to anything like their previous numbers.

This bird, often maligned and linked with death, may have prompted some to say ‘good riddance’. Yet its disappearance has carried an appalling human price. A new study puts startling figures on that cost, associating the loss of vultures with more than half a million deaths.

Research by US and UK academics indicates that mortality among people in districts hit by vulture declines rose by over 4 percent following the resulting sanitation ‘shock’. Between 2000 and 2005, this was estimated to cause annual economic damage of US$69.4 billion.

Why vultures are vital scavengers in India

As exceptionally efficient scavengers, vultures methodically consume carcasses until only bone remains, preventing flesh from decaying. Other scavenging animals, including dogs and rats, eat far less cleanly and can themselves transmit disease.

A vulture can reduce a cow carcass to a skeleton in 40 minutes. That remarkable efficiency ultimately contributed to the birds’ decline after veterinary diclofenac became available in India in 1994. Within a decade of entering the ecosystem, the vulture population fell from an estimated 50 million birds to just a few thousand.

Farmers administered diclofenac to cattle for pain and inflammation, and the drug stays in a cow’s body for roughly three days. Some ill cattle die before processing the medicine. Where costly animal incinerators are unavailable, vultures have traditionally provided the agricultural industry with a means of disposing of carcasses.

Diclofenac and the vulture population crash

However, traces of diclofenac in dead cattle poison these birds of prey by damaging their kidneys. As the birds cannot excrete it in urine, uric acid accumulates in their blood at levels reaching ten times the norm. Crystals of uric acid are frequently detected on the organs of vultures killed by diclofenac exposure.

It was only after several papers published in 2004 identified diclofenac as the vultures’ downfall that South Asian countries started prohibiting its use in livestock. By then, however, the harm had been done: this unexpected keystone species had become functionally extinct in India.

With no vultures to clear away the remains, disease spread through rotting carcasses and through the growing numbers of other disease-carrying scavengers, including rabid dogs.

Measuring the human cost of vulture loss

Environmental economists Eyal Frank of the University of Chicago and Anant Sudarshan of the University of Warwick in the UK sought to measure the human consequences of this ecological disaster.

Because reliable long-term figures for vulture populations were unavailable, the researchers combined BirdLife International data on vulture habitat with Indian drug-sales data from 1991 to 2003, particularly for diclofenac and rabies vaccinations. They also used health-outcome information from Vital Statistics of India and livestock census records.

They classified districts as affected by vulture loss where appropriate vulture habitat overlapped with livestock diclofenac use, alongside indicators of ecosystem health such as poorer water quality and large dog populations.

Between 2000 and 2005, all-cause deaths in these districts increased by an average of 4.7 percent, equating to more than 100,000 additional deaths annually. Using India’s value of statistical life of $665,000 per person, the annual cost of mortality was calculated at US$69.4 billion.

The same effects did not appear in districts not identified as dependent on vultures.

The researchers hope these stark figures may encourage policymakers to safeguard crucial species such as vultures. Though regarded as ‘dirty’ because of their association with death, they deliver ecosystem services that ultimately support human survival.

"Our results suggest that subjective existence values alone may not be the best way to formulate conservation policy," Frank and Sudarshan write.

Progress has already occurred: veterinary alternatives including meloxicam and tolfenamic acid, which do not harm vultures, have been used instead of diclofenac since India banned the drug in 2006.

Nevertheless, other anti-inflammatory medicines - ketoprofen, nimesulide and aceclofenac - have not yet been nationally banned, despite research finding that they are similarly poisonous to vultures.

The study has been accepted for publication in a forthcoming issue of the American Economic Review. Its working paper is available online through the University of Chicago.