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

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

Some may have regarded the decline of this often vilified bird, so closely associated with death, as no great loss. Yet its disappearance has carried a severe human cost: a new study puts the number of associated deaths at more than half a million.

Analysis by researchers in the US and UK indicates that human mortality rose by over 4 percent in districts hit by vulture losses, following the resulting sanitation ‘shock’. Between 2000 and 2005, this equated to estimated annual economic damages of US$69.4 billion.

How vultures keep carcasses and disease in check

As highly efficient scavengers, vultures can clean a carcass to the bone, removing muscle that would otherwise decay. Other scavenging animals, including dogs and rats, are not only less tidy feeders but can also carry disease themselves.

A vulture can reduce a cow carcass to a skeleton in 40 minutes. That very effectiveness ultimately contributed to its decline after veterinary diclofenac began to be used in India in 1994. Within just a decade of entering the ecosystem, the population fell from an estimated 50 million birds to only a few thousand.

Diclofenac is administered to cattle for pain and inflammation, and can remain in a cow’s body for roughly three days. Animals that are unwell may die before processing the medicine. In places where costly animal incinerators are unavailable, vultures have traditionally disposed of carcasses for the farming sector.

However, traces of diclofenac in cattle that have died are toxic to the birds of prey, damaging their kidneys. Because they cannot excrete it in urine, uric acid accumulates in a vulture’s bloodstream, reaching as much as ten times its usual concentration. Uric acid crystals are commonly found on the organs of vultures killed by diclofenac exposure.

It was not until several papers published in 2004 identified diclofenac as the cause of the vulture crisis that South Asian countries started banning its use in livestock. By then, however, the harm had already been done: this unusual keystone species had become functionally extinct in India.

With no vultures to clear away the remains, disease spread through both rotting carcasses and the rapid growth of other disease-carrying scavenger populations, including rabid dogs.

Vulture loss and human mortality in India

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 records of vulture population numbers over the period were unavailable, the researchers combined BirdLife International data on vulture habitat with Indian drug-sales records from 1991 to 2003, with particular attention to diclofenac and rabies vaccinations. They also used health-outcome data from Vital Statistics of India and livestock census figures.

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

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

No comparable effects appeared in districts that were not categorised as dependent on vultures.

The authors hope these stark findings may encourage policymakers to safeguard vital species such as vultures. Although they are seen as ‘dirty’ because of their connection with death, they provide 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 been made. Veterinary alternatives including meloxicam and tolfenamic acid, which are not harmful to vultures, have been used instead of diclofenac since India banned the drug in 2006.

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

The study has been accepted for publication in an upcoming edition of the American Economic Review. Its working paper is available online from the University of Chicago.