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. Vultures fulfil a vital waste-clearing role that reduces the spread of disease (such as rabies), clears rural and urban areas of odorous organic waste, and thereby also reduces the likelihood of this waste contaminating water sources. The stability of their populations is therefore of great importance to society as well as to the ecosystems in which they reside.
Vultures are a vital clean-up team. However, their ecosystem services are often outweighed by their perception in society as morbid, selfish, and harbinger’s of death due to their carcass scavenging nature. Griffon vultures of the genus Gyps were formerly very common throughout South and South-East Asia, with White-rumped Vultures 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. This suddenness of this decline is not even rivaled by that of the Dodo Raphus cucullatus. 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), with the White-rumped Vulture having declined in numbers by 99.9% since 1992 (Prakash et al. 2007; see figure). A survey in 2011 revealed that the White-rumped Vulture’s population was estimated to be 0.15% of what it was in 1992 (Prakash et al. 2012). As of 2016, all three vulture species are classified as Critically Endangered, and their population trend is still noted as declining.
Declines are also still 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).
In 2006 action was taken by the governments of India, Pakistan, and Nepal to prevent the use of the veterinary drug diclofenac and by 2008, the use, retail and manufacturing of the drug was made an imprisonable offence in India (Cuthbert et al. 2011). Surveys of cattle liver before the ban, just after the ban (late 2006), and approximately two years after the ban (late 2007, early 2008) showed concentration and prevalence to be considerably lower by the final survey. This reduction in prevalence is predicted to slow vulture declines considerably (Cuthbert et al. 2011). Whilst numbers are still very low (Prakash et al. 2012), recent surveys corroborate these predictions, with the declines of all three Gyps species slowing (Prakash et al. 2012), though uncertainty in trends is likely with such low numbers analysed.
The extinction of these vultures is still a very real possibility, making continued conservation action vital in ensuring the persistence of species of enormous ecological importance.
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Compiled: 2004 Last updated: 2017
BirdLife International (2017) Asian vulture populations have declined precipitously in less than a decade. Downloaded from http://www.birdlife.org on 28/11/2020