Posted by: barn owl | February 19, 2008

Vulture Population Declines in South Asia: I. Solving a Mystery

ResearchBlogging.org
Two species of vultures, the Turkey Vulture (Cathartes aura) and the Black Vulture (Coragyps atratus), are quite abundant here in South Texas. I frequently see them soaring above the hills west of my neighborhood, sunning themselves while perched on streetlights or dead trees, and feeding on road-killed animals (including Striped Skunks!). Old World vultures of the genus Gyps range across Europe, Africa, and Asia, and are obligate scavengers that specialize in taking the soft tissues of animal carcasses (usually ungulates). In India and Pakistan, the five species of Gyps vultures once accounted for 99% of vulture sightings. However, in the 1980s, the populations of three of these species-the White-backed Vulture (G. bengalensis), the Long-billed Vulture (G. indicus), and the Slender-billed Vulture (G. tenuirostris) declined sharply (Prakash et al., 2003).

In 2003, Pain and colleagues reviewed the possible causes and the effects of the significant decreases in the numbers of Gyps vultures throughout Asia. In Southeast Asia, and nearby Yunnan Province of China, this decline affected other scavenging birds, such as the Black Kite, the Brahminy Kite, and the Large-billed Crow. Food shortage, due to over-hunting of wild ungulates, and changes in livestock husbandry, was proposed as the primary contributor to decreases in scavenging bird numbers in this region of Asia. Across the Indian subcontinent, the numbers of Gyps vultures declined by more than 95%, and weakened birds with slumped posture and drooping necks were observed in Keoladeo National Park. Proposed reasons for the high mortality and reduced breeding success of these normally long-lived birds included food shortage, persecution through deliberate or accidental poisoning, and infectious disease. Since Gyps vultures play a crucial role as efficient scavengers, the consequences of their loss include the public health threats posed by rotting, uneaten carcasses, as well as changes in the types of scavengers that predominate near human settlements (e.g. increases in rats and feral dogs; Pain et al., 2003).

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Oriental White-backed Vulture, Gyps bengalensis
Photo: Goran Ekstrom, via Wikipedia

The Asian Vulture Crisis Project was initiated in 2000, in cooperation with the Ornithological Society of Pakistan. Mortality was measured at 2,400 White-backed Vulture nest sites across the Punjab province of Pakistan, and postmortem examinations performed on 259 adult and subadult birds. 85% of the vultures analyzed in this manner had urate deposits on internal organs, indicative of visceral gout resulting from acute kidney failure; birds that did not exhibit visceral gout instead died of trauma, lead poisoning, organophosphate poisoning, or gunshot wounds (Oaks et al., 2004). Because the toxicology results were negative for environmental contaminants typically associated with avian renal failure, and because the major food source for G. bengalensis in Pakistan is dead domestic livestock, veterinary pharmaceuticals were suspected. Indeed, residues of diclofenac, a common non-steroidal anti-inflammatory drug (NSAID) used to treat livestock, were found in 25/25 (100%) of vultures that had died of kidney failure and visceral gout. A significant number (13/20) of captive juvenile White-backed Vultures that were fed buffalo or goat carcasses injected with diclofenac developed kidney lesions, visceral gout, and renal failure (Oaks et al., 2004).

Shultz and colleagues (2004) extended these studies to include both G. bengalensis and G. indicus vultures across India and Nepal. Necropsies and toxicological analyses were performed on 15 White-backed and 13 Long-billed Vultures, collected between 2000 and 2004, across Nepal and northern India. Over 70% of these birds had visceral gout, and all 14 birds that exhibited this sign of renal failure had detectable levels of diclofenac residues. This study confirmed the results of Oaks et al. (2004) on White-backed Vultures, and demonstrated the same effects of diclofenac contamination on the much rarer Long-billed Vulture. Thus, diclofenac poisoning from livestock carcasses was found to be the most probable explanation for the precipitous declines in populations of Gyps vulture species across the Indian subcontinent.

^’^ Wednesday Wings Series, blogging on bird biology

References:

Oaks, J.L., Gilbert, M., Virani, M.Z., et al. (2004). Diclofenac residues as the cause of vulture population decline in Pakistan. Nature 427, 630-633.

Pain, D.J., Cunningham, A.A., Donald, P.F., Duckworth, J.W., Houston, D.C., Katzner, T., Parry-Jones, J., Poole, C., Prakash, V., Round, P., and Timmins, R. (2003). Causes and effects of temporospatial declines of Gyps vultures in Asia. Conserv. Biol. 17 (3), 661-671.

Prakash, V., Pain, D.J., Cunningham, A.A., Donald, P.F., Prakash, N., Verma, A., Gargi, R., Sivakumar, S., and Rahmani, A.R. (2003). Catastrophic collapse of Indian white-backed Gyps bengalensis and long-billed Gyps indicus vulture populations. Biol. Conserv. 109, 381-390.

Shultz, S., Baral, H.S., Charman, S., Cunningham, A.A., Das, D., Ghalsasi, G.R., Goudar, M.S., Green, R.E., Jones, A., Nighot, P., Pain, D.J., Prakash, V. (2004). Diclofenac poisoning is widespread in declining vulture populations across the Indian subcontinent. Proceedings of the Royal Society B: Biological Sciences, 271, S458-S460. DOI: 10.1098/rsbl.2004.0223

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