Through the collection of dead and dying vulture carcasses, researchers quickly established that 84% of dead birds in India, Nepal and Pakistan were characterized by the presence of extensive visceral gout. Visceral gout is caused by a buildup of uric acid, which at very high levels crystallizes in the body thus coating all internal organs in a white ‘paste’. The presence of visceral gout in vultures suggested that the cause of death was likely to be related to kidney failure. In fact, some birds appeared sick and lethargic for a protracted period before death, with a characteristic ‘drooping head’.

Dead birds were tested for pesticides, herbicides, toxic heavy metals and other environmental pollutants. Nonetheless researchers were baffled to find that while trace levels of some of these compounds were detected, in the majority they were at insufficient levels to cause physiological damage. Furthermore, there was no link between these compounds and the gout found in most dead birds.

Then, in 2003, came the diclofenac breakthrough. Scientific researchers recognized a link between a class of painkillers known as Non-Steroidal Anti-Inflammatory Drugs (NSAIDs) to kidney failure and cases of visceral gout in birds. The team found that the new NSAID, diclofenac, had recently come on sale and was commonly available. Investigations of carcasses showed that every bird that had visceral gout also had traces of diclofenac and those with no gout had no diclofenac.

In 2004 the results of this work were published in the journal Nature and extensive research was conducted which established the same correlation between gout and diclofenac in India and Nepal. The results showed that the dead vultures had been feeding on the carcasses of cattle that had been treated with diclofenac. Something that no one could have anticipated.

Subsequently, scientific modeling has shown that if just under 1% of cow carcasses contained diclofenac it would be enough to cause the vulture population to decline at the precipitous rate observed.

The conclusive findings on diclofenac, as the main cause of vulture declines in South Asia, led to its official ban in India. However, diclofenac is not the only vulture-toxic Non-Steroidal Anti-inflammatory Drug (NSAID) in use. Other veterinary NSAIDS are now competing in the market, namely: aceclofenac, carprofen, flunixin, ketoprofen, nimesulide, and phenylbutazone, some of which are also known or suspected to be toxic to vultures.

Currently, the only scientifically confirmed vulture-safe NSAID is meloxicam, but there are others that show promise.