As mentioned in yesterday’s post, the population of Old World vultures is in need of conservation efforts. Starting in the 1990’s a 95% population decline in the Oriental white-backed vulture was observed in Keoladeo National Park in India. Similar declines in raptor populations were reported across the Indian subcontinent. Intensive testing failed to implicate a cause; infectious disease, pesticide poisoning, starvation, and a variety of other potential causes were all dismissed. It wasn’t until 2004, that Dr. J Lindsay Oaks and colleagues proposed that the cause of this decline was related to diclofenac residues in cattle. Diclofenac is a non-steroidal anti-inflammatory drug (NSAID), commonly used to treat mild pain, fever and inflammation, and in India and Pakistan it is given to livestock to alleviate pain and keep them working longer. When cattle treated with diclofenac die, their carcass is left in a field, and vultures would feed upon that carcass. The vultures would then die of renal failure. This unfortunate situation is the result of a perfect storm of the evolutionary history of the vulture as well as the cultural practices of the people of the region.
It is worthwhile to consider what a vulture is and why they are ecologically important. It is equally important to differentiate between Old and New World Vultures. The term Old World vultures refers to those which come from Africa, north and central India, Thailand, Vietnam and other east Asian countries. While New World vultures refer to those which originate from the Americas. The New World vultures (7 species, including the Turkey vulture) are similar in many ways to the Old World vultures (15 species, including the Nubian vulture) (e.g. carrion-eating habits, bare heads, strong bills, incredible powers of flight) but the two groups have evolved separately from different ancestors. New and Old World vultures are among the world’s best examples of convergent evolution (more on this later). Regardless of their origins, vultures are natural scavengers, cleaning up carrion of wildlife and domestic livestock, in doing so, curbing the proliferation of bacteria. Vultures can eat meat at any stage of decomposition and withstand the effects that would normally kill other animals. They often eat meat that contains Botulinum toxin, anthrax and even cholera, with no effect on themselves. These birds have a very important ecological role by clearing dead animals, and if they disappear, it could result in increased cases of anthrax and brucellosis in livestock, which could spread to people.
The role of vultures in clearing the remains of livestock (and even people) is beneficial to many faiths. For instance, cattle, which are sacred to Hindus, cannot be consumed by people, thus the cattle are left for the vultures after their death. Likewise, to avoid contamination of the earth, water and fire, people of the Parsi faith, descendants of the Zoroastrians of the Persian empires, have traditionally left their dead to vultures for disposal. This has created the opportunity for the poisoning of vultures by diclofenac to occur. Interestingly, diclofenac does not cause the same toxicity observed in Old World vultures, in New World vultures.
Once the conclusions of Oaks et al. were made public, veterinary diclofenac was banned in India in 2006, however its unauthorized usage continued in some areas, despite the availability of alternatives. Meloxicam, a very similar NSAID but without the vulture killing properties, costs three to five times more than diclofenac. In light of the staggering decline in vulture populations, there are now many conservation efforts under way (see: Parahawking). One of the interesting conservation efforts is the creation of vulture restaurants. These restaurants are in protected sites and provide diclofenac-free meat for the vultures to feast upon. The “restaurateurs” buy carcasses from locals for $67/carcass, and test the meat for traces of diclofenac before putting the food out. While conservation efforts like these are great, they will fail unless the use of diclofenac in the region completely stops.