India’s Vulture Loss Linked to Over Half a Million Human Deaths

India’s vulture population collapse

A painkiller for cattle, introduced during the 1990s, triggered an unforeseen collapse in India’s vulture populations, which have yet to regain their previous numbers.

Although some may have welcomed the disappearance of this widely disparaged bird, often linked with death, its loss has carried a severe human price. New research presents startling estimates, associating the vultures’ absence with more than half a million human deaths.

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

Vultures are exceptionally efficient scavengers: they methodically consume carcasses down to the bone, preventing flesh from decomposing. Other scavengers, including dogs and rats, eat less thoroughly and can themselves spread disease.

A vulture can reduce a cow carcass to a skeleton within 40 minutes. Yet this very efficiency contributed to the birds’ destruction after diclofenac was introduced for veterinary use in India in 1994. Within a decade of entering the ecosystem, vulture numbers fell from an estimated 50 million birds to only a few thousand.

How diclofenac poisoned India’s vultures

Used to relieve cattle pain and inflammation, diclofenac can remain in a cow’s body for roughly three days. Ill cattle may die before processing the medicine, and where costly animal incinerators are unavailable, vultures have traditionally disposed of livestock carcasses for the farming sector.

However, traces of diclofenac in dead cattle poison these birds of prey and damage their kidneys. As they cannot excrete uric acid in their urine, it accumulates in their blood at levels as high as ten times normal. Uric acid crystals 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 cause of the vultures’ decline that South Asian countries started prohibiting its use in livestock. By then, however, the harm had been done and this unusual keystone species had become functionally extinct in India.

With no vultures left to clear the remains, disease spread through both decomposing carcasses and the increase in other disease-bearing scavengers, including rabid dogs.

The human cost of vulture loss

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

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

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

Between 2000 and 2005, these districts experienced an average 4.7 percent rise in deaths from all causes, 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 human mortality came to US$69.4 billion.

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

The researchers hope these stark figures may encourage policymakers to safeguard vital species such as vultures. Though regarded as ‘dirty’ because of their connection to 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.

Safer veterinary drugs after the diclofenac ban

Progress has already occurred: veterinary alternatives including meloxicam and tolfenamic acid, which are not harmful to vultures, have replaced diclofenac since India banned it in 2006.

Yet other anti-inflammatory medicines, including ketoprofen, nimesulide and aceclofenac, have still not been prohibited nationally, despite research showing that they are similarly toxic 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.