The Population Decline of Gyps Vultures in India and Nepal Has Slowed since Veterinary Use of Diclofenac was Banned

Mandar Kulkarni,Rhys E. Green,Rohan Shringarpure,Mohan Chandra Bishwakarma,Anand Chaudhary,Raphaël Arlettaz,Sachin Ranade,Khadananda Paudel,Richard Cuthbert,Vibhu Prakash,Ruchi Dave,Sashi Kumar

doi:10.1371/journal.pone.0049118

Abstract

Populations of oriental white-backed vulture (Gyps bengalensis), long-billed vulture (Gyps indicus) and slender-billed vulture (Gyps tenuirostris) crashed during the mid-1990s throughout the Indian subcontinent. Surveys in India, initially conducted in 1991–1993 and repeated in 2000, 2002, 2003 and 2007, revealed that the population of Gyps bengalensis had fallen by 2007 to 0.1% of its numbers in the early 1990s, with the population of Gyps indicus and G. tenuirostris combined having fallen to 3.2% of its earlier level. A survey of G. bengalensis in western Nepal indicated that the size of the population in 2009 was 25% of that in 2002. In this paper, repeat surveys conducted in 2011 were analysed to estimate recent population trends. Populations of all three species of vulture remained at a low level, but the decline had slowed and may even have reversed for G. bengalensis, both in India and Nepal. However, estimates of the most recent population trends are imprecise, so it is possible that declines may be continuing, though at a significantly slower rate. The degree to which the decline of G. bengalensis in India has slowed is consistent with the expected effects on population trend of a measured change in the level of contamination of ungulate carcasses with the drug diclofenac, which is toxic to vultures, following a ban on its veterinary use in 2006. The most recent available information indicates that the elimination of diclofenac from the vultures’ food supply is incomplete, so further efforts are required to fully implement the ban.

Highlights

Vultures of the genus Gyps are obligate scavengers on the carcasses of dead vertebrates; most commonly wild and domesticated ungulates
Previous road transect surveys in India, initially conducted in 1991–1993 and repeated in 2000, 2002, 2003 and 2007, revealed that, by 2007, G. bengalensis had fallen to 0.1% of its numbers in the early 1990s, with populations of G. indicus and G. tenuirostris combined having fallen to 3.2% of their earlier level [5]
They found that the high proportion of G. bengalensis and G. indicus found dead in the wild which had severe visceral gout was consistent with diclofenac poisoning being the main or sole cause of the population declines

Summary

Introduction

Vultures of the genus Gyps are obligate scavengers on the carcasses of dead vertebrates; most commonly wild and domesticated ungulates. Green et al [3] estimated that less than 0.8% of ungulate carcasses available to foraging vultures would need to contain a lethal dose of diclofenac for this to have caused the observed population declines. They found that the high proportion of G. bengalensis and G. indicus found dead in the wild which had severe visceral gout was consistent with diclofenac poisoning being the main or sole cause of the population declines. Vultures are important to human well-being in the Indian subcontinent, because they dispose of the carcasses of ungulates which would otherwise be left to rot or to provide food for the growing population of feral dogs, which cause health risks and nuisance

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Conclusion