Five charismatic vulture species that were once common throughout the Indian subcontinent are suffering precipitous population declines as a result of exposure to lethal residues of diclofenac, a veterinary painkilling drug, in livestock carcasses.
Griffon vultures of the genus Gyps were formerly very common throughout South and South-East Asia, with White-rumped Vulture Gyps bengalensis considered one of the most abundant large birds of prey in the world. Vulture populations declined across much of the region in the first half of the twentieth century, but they remained common on the Indian subcontinent, where populations were maintained by an abundant supply of livestock carcasses. In the late 1990s, however, the Indian populations of White-rumped Vulture, Indian Vulture G. indicus and Slender-billed Vulture G. tenuirostris crashed, with dramatic declines also observed in Nepal and Pakistan. Survey work in India indicated that populations of these birds had declined by c.95% in less than a decade, between 1993 and 2000, leading to their classification in 2001 as Critically Endangered (BirdLife International 2001). Current evidence suggests that populations of these species are continuing to fall rapidly (Green et al. 2004, Gilbert et al. 2006), to the extent that White-rumped Vulture has now declined in numbers by 99.9% since 1992 (Prakash et al. 2007; see figure).
Declines are also occurring in non Gyps vultures in these countries, with Egyptian Vulture Neophron percnopterus and Red-headed Vulture Sarcogyps calvus classified as Endangered and Critically Endangered respectively (Cuthbert et al. 2006, BirdLife International 2008). Although threats such as reductions in food availability and poisoning from exposure to pesticides may play a role in the declines, there is very strong evidence that the causal factor is an anti-inflammatory painkilling drug, diclofenac, which has been used widely on the Indian subcontinent since the early 1990s (Green et al. 2004, Oaks et al. 2004). Experiments show that vultures and other scavenging birds are highly susceptible to diclofenac and are killed by feeding on the carcass of an animal that has died soon after being treated with the normal veterinary dose (Green et al. 2006, Cuthbert et al. 2007, Green et al. 2007). Modelling shows that only a very small proportion of livestock carcasses need to contain a level of diclofenac lethal to vultures to result in population declines at the observed rates (Green et al. 2004). Unless the use of diclofenac is urgently controlled, the extinction of these vulture species, all of enormous ecological importance, seems imminent.
Related Case Studies in other sections
Compiled 2004, updated 2008
BirdLife International (2008) Asian vulture populations have declined precipitously in less than a decade. Presented as part of the BirdLife State of the world's birds website. Available from: http://www.birdlife.org/datazone/sowb/casestudy/113. Checked: 31/05/2016