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Understanding Endangered Vulture Diets: Implications for Conservation Strategies

A new study, a first of its kind in the Indian subcontinent, has revealed how the diet composition of threatened vulture species varies across different landscapes. Using a novel metabarcoding technique, a team of scientists from National Centre for Biological Sciences (NCBS-TIFR), Bombay Natural History Society, Department of Zoology, University of Cambridge, Karnataka Vulture Conservation Trust, and Hume Centre for Ecology and Wildlife Biology, have been able to examine faecal samples from vultures, to identify the DNA of diet species whose carcasses the vultures likely consumed. Published in the journal Biological Conservation, the findings from this study bear significant implications for conservation of vultures in India.

The study focuses on vulture species within the genus Gyps, commonly referred to as old world vultures found in India- the resident White-rumped vulture (G. bengalensis) and Indian vulture (G. indicus), and migratory Eurasian griffon (G. fulvus) and Himalayan griffon (G. himalayensis). The populations of these vultures experienced a severe decline during the 1990s and early 2000s due to the use of diclofenac in treating livestock. Diclofenac-contaminated carcasses, when scavenged by the vultures, led to widespread mortality. Particularly, populations of the three resident Gyps species (G. bengalensis, G. indicus, G. tenuirostris) witnessed a staggering decline of >95%, making them critically endangered and prompting the prohibition of veterinary diclofenac in India and neighbouring countries by 2006. Two decades later, the numbers of all three species remain low and relatively stable, with no signs of recovery. However, despite the ban on diclofenac, its illegal use in treating livestock persists and remains unregulated in many pockets of the country.

During this study, scientists gathered fresh faecal samples from all Gyps vulture species at numerous nesting and roosting sites, selected based on vulture sightings reported by the citizen science platform eBird, spanning the years 2018 to 2022. These sites were located across the states of Karnataka, Tamil Nadu, Kerala, Madhya Pradesh, Rajasthan, and Himachal Pradesh. DNA was extracted from these samples and metabarcoding analyses were conducted at the NCBS-TIFR next generation sequencing facility. Additionally, data on domestic livestock density were compiled from FAO (Food and Agriculture Organisation of the United Nations) database.

These approaches allowed scientists to identify the species consumed by the vultures. “Metabarcoding allowed us to generate data on vulture diet from large number of fecal samples very efficiently and reliably. We could use samples collected without disturbing the birds. The pipeline (designed by us) allowed us to simultaneously identify the vulture species, its sex and dietary species”, explains Dr. Mosumi Ghosh-Harihar (NCBS-inStem-Cambridge fellow, NCBS-TIFR), the lead author of the paper. Large ungulates were found to be the main dietary component for all four vulture species across all landscapes. However, diet composition, particularly the relative intake of domestic and wild ungulates differed across landscapes, vulture species and depending on whether the sample was collected inside or outside PA.

Remarkably, with the exception of PAs in South India, the three vulture species were found to be mainly feeding on domestic ungulates. This inclination is likely attributed to high availability of livestock observed in most parts of the country.  Furthermore, all vulture species have large home ranges extending beyond PA boundaries. Presence of feral livestock within PAs also makes such carcasses readily available. However, in South India, vulture species primarily scavenged on wild ungulate remains, potentially due to lower livestock carcass availability compared to regions in the north, suggest the scientists. Additionally, the South Indian states have a cultural tradition of cattle and buffalo meat consumption, which could be contributing to the diminished availability of domestic ungulate carrion for vultures.

The results of this study highlight the significant dependence of vultures on domestic ungulate carrion as a crucial aspect of their diet. Based on these results, scientists urge that continuing the efforts eliminate harmful veterinary drugs for vultures remains critical to save them from disappearing. Says Prof. Uma Ramakrishnan, Senior author, NCBS, “Gyps vultures were historically very abundant, but the use of veterinary diclofenac affected them adversely, and caused catastrophic declines. Our results emphasize the need for a continued ban on veterinary diclofenac use, as well as other NSAIDs. We hope these biological insights can contribute to on-ground population management for their conservation and recovery.”  The conservation actions include testing drugs for their impact on vultures, advocating for legal bans and ensuring enforcement and education for compliance.