South Asian Vultures
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Twenty years ago Gyps bengalensis, the oriental white-backed vulture, was considered to be possibly the most abundant large bird of prey in the world
(Pain et al. 2003). Today, a rapid population crash has led Gyps bengalensis along with Gyps indicus, the long-billed vulture and Gyps tenuirostris, the slender-billed vulture to the brink of extinction. In 1996 the status of the vultures was common and not threatened and by 2000 they were upgraded to Critically Endangered by the International Union for the Conservation of Nature and Natural Resources (IUCN), placing them among the most threatened birds in the world (Cunningham et al. 2003; Pain et al. 2003). As conservationists race to determine the cause of the sudden population crash, the loss of the vultures is causing devastating economic, ecological and religious impacts on South Asian communities.
Adult vultures range from five to ten kilograms. Gyps bengalensis are distinctive from the other species because they are slightly smaller with darker
plumage and have white on their rump, under-wing and head (Bird Life 2000). Gyps indicus and Gyps tenuirostris were once classified as the same species, but have since been separated and are now distinguished by their morphologically different bills, which lead to their common names (Cunningham et al. 2003). Gyps vultures are distributed across Asia, the Middle East, Europe and Africa (Fig.1) (Pain et al. 2003). Vultures feed primarily on carrion by scavenging the soft tissues of large mammals including the meat, offal, and intestines, but not the stomach. Vultures can take a sufficient amount of food into their crop during one meal to last for several days (Bird Life 2000). Vultures are valued as keystone species in their South Asian ecosystems due to their efficient scavenging abilities. Prior to their overwhelming decline, vultures were responsible for greater meat consumption than all mammalian carnivores combined (Pain et al. 2003).
Population declines were initially documented in breeding colonies of
Gyps bengalensis and Gyps indicus that were being monitored at Keoladeo National Park, a World Heritage Site in Rajasthan, India. The number of breeding pairs dropped steadily throughout the 90s and by 2000, there were no breeding pairs left (Prakash et al. 2003). Abnormally high morbidity and mortality rates were found among vultures with a lethargically drooping neck, which invariably lead to death in approximately 30 days (Cunningham et al. 2003).
The dramatic and unexplained population crash at Keoladeo National Park prompted the Bombay Natural History Society in 2000 to repeat a road transect survey done in Northern India from 1991 to 1993 (Pain et al. 2003). Repeat coverage of the transects showed the minimum population decline for Gyps bengalensis was 96%, which corresponded to a minimum estimated decline rate of 34% per year. Gyps indicus and Gyps tenuirostris, which were not distinguished from each other at the time showed a minimum population decline of 92% resulting in a minimum estimated yearly decline of 27% (Prakash et al. 2003). Shortly after the survey the separate identities of Gyps indicus and Gyps tenuirostris was recognised and the survey was completed
again in 2002 and 2003. Evidence from this survey showed that rates of decline are increasing, measuring an 81% decline between 2002 and 2003 in Gyps bengalensis, a 59% decline in Gyps indicus and a 47% decline in Gyps tenuirostris (Report of The International South Asian Vulture Recovery Plan Workshop 2004).
The loss of Gyps vultures is having a negative effect on the environment as well as human and animal health and well-being. Vultures used to remove all the carrion rapidly and efficiently from the environment and the acidic conditions in their stomach killed pathogenic bacteria therefore reducing the risk of spreading disease (Pain et al. 2003). Now there is an abundance of uneaten carcasses that pose a potential threat to public health because the rotting flesh provides a breeding ground for pathogenic bacteria, sources of disease, such as anthrax and can lead to water contamination (Pain et al. 2003; Prakash et al. 2003). Excessive food resources has lead to an increase in the number of small, predatory animals including feral dogs, rats and migratory scavenger birds such as Aquila nipalensis, the steepe eagle (Report of The International South Asian Vulture Recovery Plan Workshop 2004). A carcass dump in Rajsatan, India reported the number of feral dogs increased from 60 in 1992 to over 1200 in 2000. The increase in feral dog populations could have serious consequences because attacks can be fatal and the dogs are carriers of diseases that affect humans, wildlife and livestock including rabies, distemper, canine parvovirus and bubonic plague (Pain et al. 2003; Report of The International South Asian Vulture Recovery Plan Workshop 2004). Feral dogs and rats are the primary reservoirs for rabies and already more humans die from rabies in Asia than any other region in the world (Pain et al. 2003).
The declining vulture population is causing economic impacts on the people who now have to deal with the cost of disposing of the carcasses to prevent them from rotting and transmitting disease. There is also cost associated with the treatments resulting from feral dog attacks and associated diseases (Pain et al. 2003).
Gyps vultures hold a considerable amount of cultural and religious significance to the Parsee beliefs in India (Pain et al. 2003). Parsees believe that earth, water and fire are sacred and must not be tainted by human corpses (McKenzieâ„- 2000). The Parsees ritualize the practice of laying their dead in Towers of Silence, which are high walled enclosures that limit access to the corpses exclusively to airborne scavengers (Pain et al. 2003). The Parsees rely on the vultures to dispose of their dead, but with the dramatic population decline some corpses have lain uneaten for three years. The corpses are becoming health problems because of their stench and their possibility to spread infection. Due to the scarcity of the vultures smaller birds such as crows and kites are now entering the funerary sites and unlike vultures fly away with their food and have been dropping bits of the corpses outside the tower walls. The Parsees are considering sponsoring a breeding program to maintain the vultures, because
they cannot continue to let their dead rot and do not want to risk losing
their religious beliefs (McKenzieâ„- 2000).
The first step to saving the Gyps vultures is to identify the mysterious cause of their devastating population