Veterinary use of the drug diclofenac—used in the treatment of livestock—has been linked to the collapse of vulture populations throughout South Asia. Vultures are keystone species that perform a vital ecosystem service by disposing of carrion and their decline has had dramatic ecological and socio-economic consequences.
In the early 1990s, the Gyps vultures of India and South Asia were among the most abundant large raptors in the world. However, within a decade, the populations of three species, White-rumped Vulture Gyps bengalensis, Indian Vulture G. indicus, and Slender-billed Vulture G. tenuirostris, had declined so precipitously that all three are considered Critically Endangered. Surveys in India show that the country’s Indian and Slender-billed Vulture populations declined by almost 97% between 1992 and 2007. White-rumped Vultures fared even worse, dropping by 99.9 percent, to just one thousandth of their 1992 population (Prakash et al. 2007).
Extensive research has identified the cause of the decline to be ‘diclofenac’, a non-steroidal anti-inflammatory drug (NSAID) used to treat livestock (Oaks et al. 2004, Shultz et al. 2004). Vultures feeding on the carcasses of animals recently treated with the drug suffer renal failure and die. Population modelling has demonstrated that even very low rates of diclofenac contamination—between 1:130 and 1:760—are sufficient to account for the population crash (Green et al. 2004).
Vultures provide a crucial ecosystem service through the disposal of livestock carcasses and their loss has had huge socio-economic impacts across the Indian Subcontinent. Without vultures, hundreds of thousands of animal carcasses have gone uneaten—left to rot in the sun, these pose a serious risk to human health. Livestock carcasses provide a potential breeding ground for numerous infectious diseases, including anthrax, and encourage the proliferation of pest species, such as rats.
Most worryingly, the loss of vultures has resulted in an increase in the number of feral dogs around carcass dumps—the bites of which are the most common cause of human rabies in the region. A recent study in India estimates that, concurrent with the vulture die-off, there has been an increase in the feral dog population of at least 5.5 million (Markandya et al. 2008). It is calculated that this has resulted in over 38.5 million additional dog bites and more than 47,300 extra deaths from rabies. The researchers believe that the increased number of rabies victims may have cost the Indian economy $34 billion.
In 2006, the governments of India, Pakistan and Nepal introduced a ban on the manufacture of diclofenac and pharmaceutical firms are now encouraged to promote an alternative drug, ‘meloxicam’, which is proven to be safe for vultures and an effective treatment for livestock (Birdlife International 2006, Swan et al. 2006). The manufacturing ban has had some success in reducing the drug’s prevalence—for example the use of diclofenac has dropped by 90% in local areas within Nepal (Birdlife International 2008) and, across India, contamination of cattle carcass with diclofenac has fallen by nearly a half, down from 10–11% before and around the time of the ban to 6.5% in 2007–2008; a reduction that has led to a fall in the estimated decline in the vulture population to 40% of the rate before the ban (Cuthbert et al. 2011a). Unfortunately, misuse of human forms of diclofenac in the veterinary sector remains a significant threat to vultures, along with the wide-scale use of untested veterinary medicines in the region (Cuthbert et al. 2011b). However, in spite of these ongoing threats, recent surveys suggest vulture numbers have stabilized in South Asia as a consequence of actions to ban diclofenac (Jamshed et al. 2012, Prakash et al. 2012), although numbers remain very low across the region and any recovery will be slow.
Related Case Studies in other sections
Compiled 2008, updated 2013
BirdLife International (2013) Vultures are under threat from the veterinary drug diclofenac. Presented as part of the BirdLife State of the world's birds website. Available from: http://www.birdlife.org/datazone/sowb/casestudy/156. Checked: 20/04/2014