Beauty may be in the eye of the beholder, but it’s fair to assume that vulture looks are an acquired taste. The hook-beaked, scrawny-necked and chunky-bodied birds were immediately described as “disgusting” by English biologist Charles Darwin, although his revulsion was also due to the vultures’ diet of dead animals. Yet that same stomach-churning tendency also causes vultures to be indispensable to human ecosystems, since the rotting carcasses contain dangerous diseases that could spread to humans if not ingested by more iron-stomached scavengers.
In fact, a recent study in the journal American Economic Review revealed that the unintentional decimation of India’s vulture population has had tragic consequences for nearby humans. Scientists estimate that their near-disappearance on the subcontinent nearly two decades ago — an unintentional byproduct of human activity — has led to more than half a million excess deaths.
“Our study provides strong evidence that the anecdotal reports of a public health crisis following the collapse of vultures were capturing a true signal: human health deteriorated following the collapse of the vultures,” study lead author Dr. Eyal Frank of the University of Chicago told Salon. “Before our study, there were anecdotal reports and claims, some back-of-the-envelope calculations about the potential magnitude of the effect, but our study uses annual district level data to quantify these impacts, and manages to reject other alternative explanations for the increase in mortality we observe.”
Frank and fellow University of Chicago professor Anant Sudarshan classified “district” as any high or-low-suitability area for affected vulture species, then analyzed the existing data to compare all-cause human mortality rates in those districts over the past two decades. “Before the collapse of vultures, there was no systematic difference in how those two groups were trending,” Frank said. “After vultures collapsed, we observe that the all-cause death rate in the high-vulture-suitability districts diverged from the low-vulture-suitability districts. By 2000, when vulture populations were effectively at their new population levels (less than 5% of their original population levels), we see that the divergence stabilizes.”
The collapse occurred because of indirect actions from the agricultural industry, specifically farmers treated their cattle with an anti-inflammatory medicine, called diclofenac, that proved highly toxic to vultures. Even worse, a generic version had become increasingly popular, meaning that vultures regularly were poisoned by dead animals exposed to the pharmaceutical. The new study found other indicators that this drug’s presence played a role in the current ecological crisis.
“We also report results that demonstrate that water quality deteriorated in the high-vulture-suitability districts, and that at the national level, there was an increase in the sales of rabies vaccines — consistent with the two main mechanisms highlighted by ecologists and public health experts,” Frank said.