Vultures are considered a “keystone species” critical to their surrounding habitat because, as highly-efficient scavengers, they play an important sanitation role. Farmers have long relied on them to remove the rotting bodies of dead livestock. But vultures in India came close to extinction in the mid-1990s after an anti-inflammatory drug (diclofenac) used to treat cattle poisoned and killed the birds. A new study in a forthcoming edition of American Economic Review uses their sudden collapse to explore the impacts on human health and finds that their absence led to the death of about 100,000 people a year over five years.
“Vultures are considered nature’s sanitation service because of the important role they play in removing dead animals that contain bacteria and pathogens from our environment—without them, disease can spread,” says study co-author Eyal Frank, an EPIC scholar and assistant professor at the Harris School of Public Policy. “Understanding the role vultures play in human health underscores the importance of protecting wildlife, and not just the cute and cuddly. They all have a job to do in our ecosystems that impacts our lives.”
Frank and his co-author Anant Sudarshan, from Warwick University, compared human death rates in Indian districts that once thrived with vultures to areas with historically low vulture populations both before and after the vulture collapse. They found that just after the anti-inflammatory drug sales rose and vulture population collapsed, the human death rate increased by more than 4 percent in the districts where the birds once prospered. The effect was the greatest in urban areas with large livestock populations where carcass dumps occur on the outskirts of town. The authors estimated that, between 2000 and 2005, the loss of vultures caused about 100,000 additional human deaths each year, resulting in $69.4 billion per year in mortality damages.
The deaths stemmed from the proliferation of disease and bacteria that the vultures would have ordinarily removed from the environment. Without them, the dog population increased and brought rabies to humans. The sale of rabies vaccines increased during this time—but were not enough. Because the dogs were not as good as the vultures at cleaning the rotting remains, bacteria and pathogens spread to the drinking water through runoff and poor disposal methods. Fecal bacteria in the water more than doubled.
“The vulture collapse in India provides a particularly stark example of the type of hard-to-reverse and unpredictable costs to humans that can come from the loss of a species,” says study co-author Anant Sudarshan, an EPIC non-resident scholar and associate professor at the University of Warwick. “In this case, new chemicals were to blame, but other human activities—habitat loss, wildlife trade, and now climate change—have an impact on animals and in turn on us. It’s important to understand these costs and target resources and regulations towards preserving especially these keystone species.”