Once a common sight across India, vultures were abundant scavengers, often seen circling landfills in search of carcasses. However, their populations began to plummet in the mid-1990s due to the widespread use of diclofenac, a veterinary painkiller that proved fatal to these birds.
Diclofenac, while effective for treating livestock, led to kidney failure and mass mortality in vultures. By the mid-1990s, the Indian vulture population, once estimated at 50 million, had drastically declined to near extinction.
Although the use of diclofenac in veterinary medicine was banned in 2006, the impact on vulture populations remains significant. The latest State of India's Birds report indicates that at least three vulture species have experienced population declines of 91-98%.
The consequences of this ecological disaster extend beyond the loss of these magnificent birds. A recent study published in the American Economic Association journal revealed a tragic human toll. With the decline of vultures, there was a significant increase in the number of feral dogs, which became the primary scavengers. This led to a rise in rabies cases and a subsequent surge in human rabies deaths. The study estimates that the decline of vultures resulted in approximately half a million human deaths over a five-year period.
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. 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.
Authors compared human death rates in Indian districts that once thrived with vultures to those with historically low vulture populations, both before and after the vulture collapse. They also examined rabies vaccine sales, feral dog counts and pathogen levels in the water supply.
They found that after anti-inflammatory drug sales had risen and vulture populations had collapsed, human death rates increased by more than 4% in districts where the birds once thrived.
The researchers also found that the effect was greatest in urban areas with large livestock populations where carcass dumps were common. Between 2000 and 2005, the authors estimate that the loss of vultures contributed to an additional 100,000 human deaths each year. This tragic toll resulted in an economic loss of more than $69 billion (£53 billion) annually, reflecting the costs associated with premature mortality.
These deaths were largely caused by the unchecked spread of bacteria and diseases that vultures would typically have removed from the environment. In the absence of vultures, the stray dog population grew significantly, leading to an increase in rabies transmission to humans.
Although sales of rabies vaccines rose during this period, they were not enough to counteract the growing risk. Unlike vultures, dogs could not effectively clear decaying animal remains, which allowed harmful bacteria and pathogens to spread into water supplies, especially through runoff and improper disposal practices. As a result, the level of faecal bacteria in drinking water more than doubled.