Assam records world’s first-ever release of captive-bred slender-billed vultures
Captive-bred slender-billed vultures were released into a soft-release aviary in Assam for the first time anywhere in the world, marking a milestone in vulture conservation breeding programmes.
The release was carried out by a national park and tiger reserve authority in collaboration with a wildlife research organisation running the associated vulture conservation breeding centre.
The move is aimed at rebuilding the wild population of slender-billed vultures, which breed naturally in the release landscape but have suffered a severe historical population collapse.
The breeding centre involved has bred dozens of slender-billed vultures to date and has reached a stage where it can release a small annual cohort of captive-bred birds into the wild.
Gyps Vulture Population Collapse and the Diclofenac Crisis
Populations of India's three resident Gyps vulture species (white-rumped, Indian/long-billed, and slender-billed vultures) collapsed by more than 95-99% between the early 1990s and mid-2000s, one of the fastest declines ever recorded in a wild bird population. The cause was identified as diclofenac, a cheap non-steroidal anti-inflammatory veterinary drug widely used on cattle; vultures feeding on carcasses of recently treated animals ingested residual diclofenac, causing fatal kidney (visceral gout) failure. India, along with Nepal and Pakistan, banned the veterinary (though not human) use of diclofenac in 2006, which has since been credited with slowing, and in some areas reversing, the decline.
Key Details
- Population decline: over 95-99% for the affected Gyps species between the early 1990s and mid-2000s.
- Cause: diclofenac-induced kidney failure (visceral gout) in vultures feeding on treated-cattle carcasses.
- Veterinary diclofenac banned in India: 2006 (human-use formulations remain legal, a continuing regulatory loophole/enforcement gap).
- Post-ban studies show the rate of decline has slowed, and in some regions population trends have stabilised or reversed.
The captive-breeding-and-release programme exists precisely because wild populations collapsed to critically low numbers due to diclofenac poisoning; releasing captive-bred birds is a direct conservation response to restore numbers that natural breeding alone cannot recover quickly enough.
Legal and Conservation Status of the Slender-Billed Vulture
The slender-billed vulture (Gyps tenuirostris) is classified as Critically Endangered on the IUCN Red List, with fewer than roughly 1,000 mature individuals estimated to remain. Domestically, it receives the highest legal protection available under Indian law, being listed in Schedule I of the Wildlife (Protection) Act, 1972, which prescribes the most stringent penalties for hunting, trade, or harm to the species. It is also listed under Appendix II of both CITES (Convention on International Trade in Endangered Species) and CMS (Convention on Migratory Species), placing additional international obligations on regulating its trade and cross-border conservation.
Key Details
- IUCN status: Critically Endangered (assessed since the early 2000s due to the diclofenac-driven crash).
- Wildlife (Protection) Act, 1972: Schedule I — highest protection tier, on par with species such as the tiger.
- International listings: CITES Appendix II, CMS Appendix II.
- Species range: primarily the Indian subcontinent and parts of Southeast Asia, with India hosting significant surviving wild populations, including in northeastern grassland/forest landscapes.
The species' Schedule I/Critically Endangered status is what justifies the intensive, resource-heavy captive-breeding and soft-release intervention described in the news; such extraordinary measures are typically reserved for species facing imminent extinction risk under the highest protection categories.
Conservation Breeding Centres and Soft-Release Methodology
Vulture Conservation Breeding Centres (VCBCs) are specialised captive-breeding facilities set up in India (in states including Haryana, West Bengal, Assam, and Madhya Pradesh) since the mid-2000s, run in partnership between state forest departments and conservation NGOs, to breed the three critically endangered Gyps species away from diclofenac-contaminated carrion. "Soft release" is a phased reintroduction method in which captive-bred animals are first placed in a supervised, semi-enclosed aviary at the release site to acclimatise to local conditions, food sources, and social structures before being allowed to fly free, improving post-release survival compared to a direct ("hard") release into the wild.
Key Details
- VCBCs in India were established from the mid-2000s onward, in the years following the identification of diclofenac as the cause of the vulture crash.
- Breeding centres operate under state forest department oversight with technical/NGO partnership support.
- Soft-release aviaries allow gradual acclimatisation, distinct from direct hard release, and are the standard global practice for reintroducing captive-bred raptors.
- Annual release cohorts from mature breeding programmes are typically small (single digits to low tens of birds), reflecting the slow breeding rate of vultures (they lay a single egg per breeding cycle).
The Assam release exemplifies the soft-release methodology used globally for critically endangered raptors, and its status as a world-first for the slender-billed vulture specifically marks the maturation of India's decades-long captive-breeding effort from pure breeding success to actual wild-population reinforcement.
- Slender-billed vulture: IUCN status Critically Endangered; Schedule I species under the Wildlife (Protection) Act, 1972.
- Gyps vulture population decline in India: over 95-99% between the early 1990s and mid-2000s, driven by diclofenac poisoning.
- Veterinary diclofenac banned in India (also Nepal, Pakistan): 2006.
- This release is described as the world's first release of captive-bred slender-billed vultures into the wild.
- Release method: soft release via a supervised aviary at the reintroduction site, the standard practice for critically endangered raptor reintroduction.