Thinning of vulture populations in the Indian subcontinent

March 31, 2015 by  
Filed under Features

Vultures constitute an important component of the ecosystem. Being carrion feeders, they perform an important task as finishers in the ecosystem in returning human and animal corpses into their elemental forms back into the system and thus play a significant role as cleaners or disposers in the nature. They are capable of stripping carcasses free of all flesh, soft and hard tissues such as tendons, cartilages, softer bones, skins, hairs and keratins with their sharp claws and beaks; and due to special enzymes in their stomach are capable of digesting them. Different species of vultures are reported from the Indian subcontinent and unfortunately the populations of most of these ecologically important species are showing serious signs of decline across most of their natural ranges. Some of the factors that have contributed towards the rapid decline of the populations of different species of vultures across the subcontinent include: loss of habitats and habitat fragmentations; removal of old and big trees in and around city fringes, city parks and city gardens causing loss of suitable nesting sites; rapid and unplanned urbanization drive to cater to the growing human populations in the cities and towns; unprecedented boom of real estate business and infrastructural developments causing the loss of green spaces within and around the major city areas, the added areas and their subsequent extensions and in the greater metropolitan areas including district towns and municipalities; rapid, unrestricted, unplanned and unmonitored growth of both legal as well as illegal industrial units within city limits and adjacent areas causing pollution of the local environment; severe anthropogenic pressures in the remaining open spaces at the city fringes due to human encroachments and establishments of slums and shanties; communicable diseases among vulture populations; and last but not the least, poisoning of the animal carcasses on which these birds feed as their primary food sources both intentionally as well as accidentally. Furthermore, pesticide poisoning of the birds have also been reported from several parts of the subcontinent.

Subsequent scientific studies established that diclofenac, an anti-inflammatory drug commonly administered to the Indian livestock for the treatment of wounds and inflammations, as one of the potent chemicals that have been killing and decimating the vulture populations in India through the process of biomagnification. The leading cause of death through poisoning by the drug among vultures is through drastic renal failures. The species that have been worst impacted are the Indian vulture (Gyps indicus Scopoli), the white-rumped vulture (Gyps bengalensis Gmelin) and the slender-billed vulture (Gyps tenuirostris Hodgson (in Gray)); that were reduced from stable populations of several millions to just a few thousands over the span of two-three decades.

In several parts of their former ranges a decline between >70-85% to < 97-99% in their wild populations have been reported raising an important concern for their threats to extinction in the next 20-25 years.  Unfortunately, the Indian vulture, the slender-billed vulture and the white-rumped vultures are all now placed under the category of critically endangered by the IUCN; while the Egyptian vulture (Neophron percnopterus Linnaeus) is currently considered to be endangered. The only species that is evaluated to be near threatened in the wild is the famous Himalayan vulture or better known as the Himalayan griffon vulture (Gyps himalayensis Hume) that is restricted to the Himalayas and the Tibetan plateau and is not dependent too heavily upon livestock carcass as their principal dietary source; and the Eurasian griffon (Gyps fulvus Hablizil) which is under the least concern category. The facts clearly indicate that the vultures belonging to the genus Gyps are most readily impacted and also these species are distributed predominantly in the river valleys, great northern and western plain lands and the plateau region of the subcontinent with significant agronomic activities and substantial livestock populations. Hence the biomagnification poisoning through diclofenac has been identified as one of the most devastating factors decimating the vulture populations in the Indian subcontinent in addition to several other anthropogenic factors mentioned above.

Several vulture rehabilitation, breeding and reintroduction centers have been established in India being alarmed with the sharp decline of the vulture populations and a few more are coming or are being proposed. However, their numbers are too meager compared to the need from the context of species revival. Some success has been documented in the breeding, rearing and reintroduction of different vulture species in the wild in various parts of their former home ranges; however, much needed to be done. Steps have been taken in removing diclofenac as the preferred veterinary drug by the cattle handlers and livestock operators with other alternatives having much lower impacts on the vulture populations has been recommended and/or prescribed. But the drug is continued to be used in small to moderate numbers till date across the home range of the vultures. Lack of education and awareness; as also lack of care and empathy for the long term sustainability of the local ecosystem and environment by agricultural workers, cattle handlers and livestock operators have been another serious concern that needs to be addressed sincerely by the vulture conservation agencies. It will be necessary to completely ban this drug from the livestock industry and strong monitoring and surveillance will be necessary to evaluate the wild populations of vultures in the coming decades. Unless a comprehensive conservation, rehabilitation and reintroduction policy is adopted with strong legislative measures and effective wildlife management strategy is implemented and practiced in saving the Indian vultures, their future looks extremely grim and vulnerable with dangers of extinction in the wild.

Article contributed by: Saikat Kumar Basu

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