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Rapid population declines and mortality clusters in three Oriental white-backed vulture Gyps bengalensis colonies in Pakistan due to diclofenac poisoning


Martin Gilbert a1p1, Richard T. Watson a1, Munir Z. Virani a1, J. Lindsay Oaks a2, Shakeel Ahmed a3, Muhammad Jamshed Iqbal Chaudhry a3, Muhammad Arshad a3, Shahid Mahmood a3, Ahmad Ali a3 and Aleem A. Khan a3
a1 The Peregrine Fund, 5668 West Flying Hawk Lane, Boise, ID 83709, USA. E-mail mgilbert@wcs.org
a2 Department of Veterinary Microbiology and Pathology, Washington State University, Pullman, WA 99164-7040, USA
a3 The Ornithological Society of Pakistan, 109/D P.O Box 73, Dera Ghazi Khan, Pakistan

Article author query
gilbert m   [PubMed][Google Scholar] 
watson rt   [PubMed][Google Scholar] 
virani mz   [PubMed][Google Scholar] 
oaks jl   [PubMed][Google Scholar] 
ahmed s   [PubMed][Google Scholar] 
chaudhry mji   [PubMed][Google Scholar] 
arshad m   [PubMed][Google Scholar] 
mahmood s   [PubMed][Google Scholar] 
ali a   [PubMed][Google Scholar] 
khan aa   [PubMed][Google Scholar] 

Abstract

The population declines affecting Asian Gyps vultures are among the most rapid and geographically widespread recorded for any species. This paper describes the rates and patterns of mortality and population change over 4 years at three Oriental white-backed vulture Gyps bengalensis colonies in Pakistan: Dholewala (initially 421 pairs), Toawala (initially 445 pairs) and Changa Manga (initially 758 pairs). Vulture mortality led to the extirpation of two of these colonies (Changa Manga and Dholewala) in 3 years, and a decline of 54.3% in the third. Visceral gout, indicative of diclofenac poisoning, was the largest single cause of death in vultures examined. Annual adult mortality from diclofenac poisoning was significantly positively correlated with annual population declines at each colony indicating a direct causal relationship. Visceral gout occurred in temporal and spatial clusters suggesting multiple point sources of diclofenac exposure. The spatial and temporal distribution of dead vultures and approximate time since death were used to estimate minimum rates at which colonies encountered carcasses with sufficient diclofenac to cause mortality of 1.26–1.88 carcasses per colony per month. By estimating total carcass consumption at each colony, the percentage of carcasses contaminated with diclofenac was calculated as 1.41–3.02%, exceeding the minimum required to have caused the observed population decline. With populations declining by approximately 50% annually, the long term survival of Gyps vultures in South Asia will require the removal of diclofenac from vulture food and establishment of captive populations for future restoration once the environment is free from contamination.

(Published Online January 5 2007)
(Received January 12 2006)
(Revised April 6 2006)
(Accepted October 10 2006)


Key Words: Diclofenac; Gyps bengalensis; mortality cluster; Pakistan; population decline; visceral gout; vulture.

Correspondence:
p1 Current address: Wildlife Conservation Society, 2300 Southern Boulevard, Bronx, NY 10460, USA


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