Vulture population decline , Diclofenac and avian gout

Populations of the Gyps vultures of southern Asian countries have been declining precipitously during the recent past, especially in the western parts of its distributional range. A linkage between the common non-steroidal anti-inflammatory drug (NSAID) ‘Diclofenac’ and the mortality of these vultures was established recently from Pakistan. However, any conclusive evidence on Diclofenac-poisoning is still lacking from the Indian region, where the degree of decline has been severe. Post-mortem examinations of vulture carcasses revealed visceral gout (deposition of uric acid crystals in the tissues) as the cause of mortality in most of the dead birds. The visceral gout condition could be induced by a variety of potential factors, mostly associated with environmental degradation and climate changes. It appears quite likely that many such factors together have made a cumulative contribution towards the observed population decline of Gyps vultures during the recent years, which has pushed these scavenging sky-lords to near extinction. However, because of the scarcity of studies available on the impact of these factors on vultures, the factors would remain speculative until confirmed through empirical studies. Our aim is to provoke and direct further research in this direction. It is also intended to highlight the need for examining many of the pharmaceuticals and personal-care products from the point of view of their ecological impacts. The Oriental white-backed vultures (OWBV; Gyps bengalensis), also known as white-rumped vultures, are distributed in southern Asia from Indus Valley of Pakistan in the west to Thai–Malay peninsula in the east (Figure 1) and have historically been the commonest vulture species of the area. The OWBVs were once so common in South Asian countries, that their abundant presence high in the skies even posed a serious threat to smooth air traffic. In the changed scenario, these once-common species have become rare and have made their way to the latest Red Data Book under the critically endangered category. According to the Red Data Book, ‘it (OWBV) has suffered an extremely rapid population decline, particularly across the Indian subcontinent, probably as a result of disease compounded by poisoning, pesticide use and changes in the processing of dead livestock’. Populations of all the three Gyps vultures of the area, namely the white-backed vulture (Gyps bengalensis; Figure 2), Indian vulture or long-billed vulture (Gyps indicus indicus) and slender-billed vulture (Gyps indicus tenuirostris) have declined drastically to below-sustainable limits throughout their distributional range. Considering the current pace of decline, the extinction of these species from the face of the earth appears all too imminent. Although populations of OWBVs have been declining moderately in the eastern parts of its distributional range from early last century itself, this slow decline could be attributed to habitat alterations and changes in food availability. The OWBV populations in the western parts of its range remained healthy until early last decade and showed a sudden and sweeping decline during the nineties. As early as 1993 itself the population decline and even local extinction of this species were reported from certain pockets of the country, and it was only during recent times that this cataclysmic population decline received serious attention from conservationists and the general scientific community of the country. The magnitude of decline and frequent sightings of dead vultures indicated that the enhanced mortality rate due to unknown reasons is causing the population decline. Further, investigations revealed characteristic symptoms of visceral gout in most dead birds, which was diagnosed as the cause of mortality. The ecology and population dynamics of the OWBVs are poorly known. It is unfortunate that except a doctoral thesis and a few related publications reported from the Gir forest, Gujarat, there is not much literature available in the public domain of the country on ecological aspects of these birds, crucially important in the ecosystem as efficient scavengers. Most of the documented information about them is in the form of grey literature as occasional short notes based on opportunistic observations. Many of such articles discuss various ecological and behavioural aspects of the species such as feeding, breeding and interspecific interactions. However, these isolated fragments of information are of little use for devising a crisis management plan to save the species, which would demand a comprehensive information base. Once the population decline came to the limelight, various possible causes such as pesticide contamination, mass killing by people (poisoning/shooting) and a contagious viral disease were examined by ornithologists. However, none of these