The role of research in vulture conservation
Research has been at the core of vulture conservation in Asia since the early days of the Vulture Crisis. It was through monitoring of vulture nests at Keoladeo National Park in Rajasthan, India, that the first indication of population declines was noted – from a high of ca.350 nests in the mid-1980s, the colony of White-rumped Vultures went extinct by 1999. This was confirmed as a national problem by a repeat of road transect surveys initially carried out in 1992/93. Subsequent surveys highlighted the scale of the issue, showing that populations of vultures had declined by more than 95% (Prakash et al. 2007).
The cause of these staggering declines was unknown for several years until work carried out by the Peregrine Fund discovered the culprit to be the non-steroidal anti-inflammatory drug (NSAID), diclofenac (Oaks et al. 2004). This drug proved to be highly toxic to vultures that consumed it while feeding on the carcasses of cattle that had been treated with diclofenac shortly before death. Ultimately, veterinary use of diclofenac was banned by the governments of India, Pakistan, Nepal and Bangladesh, a process made easier by the discovery of a NSAID that was safe to vultures – meloxicam (Swan et al. 2006, Swarup et al. 2006).
Since the ban on diclofenac, scientific research has played a key role in monitoring the efficacy and success of conservation actions carried out to protect vultures, and publication in peer-reviewed scientific journals is seen as a vital step for such work to be accepted in the region.
Monitoring of vulture populations
The most basic step in the conservation of any species is to understand how populations are faring. In India and Nepal, road transect surveys have been carried out on a regular basis by teams from Bombay Natural History Society (BNHS) and Bird Conservation Nepal (BCN), covering over 15,000 and 700 km respectively. Results from these surveys have demonstrated that, after the catastrophic declines first witnessed in India, populations have since stabilised at a new low level (Prakash et al. 2024). However, in Nepal, there has been evidence that conservation, in the form of ridding the country of diclofenac and the promotion of the use of meloxicam, has had a positive effect, with a partial recovery in both White-rumped and Slender-billed Vulture populations (Galligan et al. 2020). In fact, populations of White-rumped Vultures are increasing at as fast a rate as is possible for a vulture (BCN, unpublished data).
Elsewhere in Asia, a variety of methods are used to monitor vulture populations and productivity, including monitoring of nesting colonies and sites for White-rumped and Indian Vultures in Pakistan, Bangladesh and Nepal (SAVE 2015), and counts of White-rumped, Slender-billed and Red-headed Vultures at multiple feeding stations in Cambodia.
Monitoring the prevalence of NSAIDs
The key conservation action taken to prevent the extinction of vultures in South Asia was the ban on the manufacture, distribution and use for veterinary purposes of the NSAID diclofenac. This was greatly facilitated by the promotion of meloxicam as a vulture-safe alternative. Since the ban on diclofenac, it has been necessary to monitor its illegal use on domestic animals. We have done this in two ways: undercover pharmacy surveys and analysis of cow liver samples. Surveys of pharmacies have involved local men asking pharmacists for a drug to treat a sick cow, who then buy the first drug offered them. Why undercover? Well, use of diclofenac is illegal, and if we were up-front regarding our motives, we would likely get a biased picture of diclofenac use. Results of these surveys have shown that, in India, illegal use of diclofenac is still widespread, while in Nepal and Bangladesh, the drug has virtually disappeared (Galligan et al. 2021). However, diclofenac is not the only vulture-toxic drug on the market (see below), and other such drugs were commonly used, e.g. ketoprofen in Bangladesh and nimesulide in India and Nepal. Although the use of toxic drugs is worrying, the good news was that the vulture-safe meloxicam had become the drug of choice to treat cattle throughout the region.
Analysis of cow liver samples gives a more direct measure of the prevalence of different drugs in the vulture food chain. We sample liver tissue from mainly cattle and buffalo carcasses left for scavengers to consume in India and Nepal. These samples are analysed for presence and concentration of NSAID residues using liquid chromatography mass spectrometry. Early work showed that the prevalence of diclofenac in cattle carcasses was by far high enough to have been the main, if not sole, cause of the catastrophic vulture declines (Green et al. 2004). Carcass surveys have shown that diclofenac use in India has halved since the ban on veterinary diclofenac; and meloxicam use has increased by almost one half (Cuthbert et al 2014).
Identifying new vulture-toxic and vulture-safe NSAIDs
Experimental safety testing of diclofenac confirmed that it was toxic to vultures and the cause of the population declines (Oaks et al. 2004). Likewise, such testing proved that meloxicam was safe to these obligate scavengers (Swan et al. 2006). Safety testing involves giving a dose of a drug to vultures at levels they are likely to encounter when feeding on cattle in the wild. If the drug is toxic, unfortunately this will result in the death of the vultures, so our experiments are designed to minimise vulture mortalities and meet international animal ethical standards, i.e. no more than two vultures are ever given a toxic drug.
Since the testing of diclofenac and meloxicam, safety testing has been carried out on several other NSAIDs in collaboration with BNHS, Indian Veterinary Research Institute (IVRI), University of Pretoria and Vulpro (South Africa). Drugs such as aceclofenac (Galligan et al. 2016, Chandramohan et al. 2022), ketoprofen (Naidoo et al. 2009), carprofen (Naidoo et al. 2010) and nimesulide (Galligan et al. 2022, Mathesh et al. 2023) have proven to be toxic to vultures. As a result, aceclofenac, ketoprofen and nimesulide have been the subject of bans in various countries in the region. However, it is also important to identify other vulture-safe drugs to give livestock owners more choice in how they treat their sick animals. Up until recently, meloxicam was the only such drug, but recently safety testing has identified tolfenamic acid as the second verified vulture-safe NSAID (Chandramohan et al. 2021).
Monitoring wild and captive-released vultures with satellite telemetry
In Nepal, BCN has been monitoring individual vultures through the use of satellite and GPS telemetry. This involves fitting birds with transmitters, weighing between 30-50g (ca.1% of vulture body weight), with the use of a Teflon harness (Anderson et al. 2020). Since 2017, a total of 70 wild White-rumped Vultures have been trapped at the Jatayu Restaurant at Pithauli near Chitwan National Park and fitted with transmitters. Over the same period, all 69 birds were released and from the conservation breeding population and also fitted with transmitters. There are several benefits to satellite / GPS tracking. Firstly, and most obviously, you are able to follow the movements of birds in virtually real time, finding out where they go; in this way, we know where important feeding sites are located, and new nesting colonies have been identified. Secondly, you obtain an estimate of annual survival. Only two decades ago in this area, as across the whole of South Asia, populations were declining by 50% per year (Green et al. 2004). Through tracking, we have been able to estimate current annual survival for adults as 97% and for subadult birds, 90% (Mallord et al. 2024). This is comparable to survival rates of Gyps vultures elsewhere in the world, and suggests that the environment is free from diclofenac, as well as other sources of human-caused mortality. Thirdly, daily monitoring of these birds allows us to find birds soon after they die. These can then be retrieved and sent for post-mortem. In this way, we get an unbiased picture of the most important causes of mortality, and have been able to confirm that no birds died from NSAID poisoning. Finally, by monitoring released birds, we can see how well they are assimilating into the wild population. Perhaps not surprisingly, after several years in captivity, it has taken a little while for birds to become acclimatized to their new surroundings, and many have not moved from the release site, where they are still provided with food twice-weekly. However, an increasing number of the released birds, especially those that were released as subadults and that have now reached sexual maturity, have started nesting around the release site, sometimes as all-released pairs, other times paired with a wild-born bird. In 2021, the first chick from a released pair successfully fledged.
The socio-economic costs of the vulture decline
Vultures are obligate scavengers, removing vast numbers of animal carcasses from the environment, an ecosystem service that can halt the spread of disease. Since the loss of vultures, there has been a dramatic increase in feral dog populations that has led to an increase in human-dog interactions, including attacks, and may have led to an increase in rabies cases (Markandya et al. 2008). Furthermore, a recent study (Frank & Sudarshan 2024) has found that an increase in all-causes human mortality of over 4% can be attributed to the loss of vultures and the ecosystem services they provide. A staggering excess of 500,000 human deaths over just 5 years has been estimated (Frank & Sudarshan 2024).
Access some of the key research papers and reports that underpin our programme here.