When hiking in the Pyrenees or other mountain ranges, it is very likely that you will encounter very large birds of prey, soaring through the sky. These are vultures: birds of prey that are often necrophagous, i.e. they feed on dead things. Reflecting their scavenging lifestyle and unlike other birds of prey, they are very heavy and do not have very sharp talons, only an extremely strong neck and beak for tearing dead flesh. In the Pyrenees, the griffon vulture Gyps fulvus can easily be spotted in groups of several individuals. During our field sessions in the Pyrenees, we were lucky enough to see the bearded vulture (Gypaetus barbatus), whose unique trait is to eat bones. Indeed, vultures have an extremely low stomach pH (very acidic) which can digest almost anything. There is also the Egyptian vulture (Neophron percnopterus) and, only on the Spanish side of Catalonia, the Cinereous vulture (Aegypius monachus), recently introduced in France, with success (but not in the Pyrenees).
Vultures are often very badly perceived and humans have long persecuted these animals, either by destroying their nests or by removing or poisoning their food, that is, the carcasses (with strychnine for example). This shows a great lack of understanding of the enormous ecological importance of these magnificent creatures. Vultures are one of nature's most efficient scavengers and provide essential services to the ecosystem. They allow the flow and recycling of nutrients and energy through ecosystems. By disposing of carrion and other organic waste, vultures provide a free and efficient cleaning service. In doing so, they limit the spread of pathogens on carcasses and, more importantly, the proliferation of other scavenging mammals (feral dogs, foxes, rats, etc.) which, because of their closer taxonomic relationship with us (humans), are more likely to transmit zoonotic diseases. Unfortunately, vultures are in decline worldwide, along with the rest of biodiversity. There are many reasons for this, but anthropogenic poisoning is one of the main causes. A prime example is diclofenac, a non-steroidal anti-inflammatory drug (NSAID) widely used by humans for their own good (marketed as Voltaren®) but also for livestock. When these livestock die in remote landscapes such as mountains, the first to know are the vultures and they will ingest some of the carcasses containing diclofenac.
While diclofenac is well metabolised and therefore relatively safe in most mammalian species, it is not tolerated in vulture species at the same dose. It is all a question of metabolism. From a veterinary point of view, in simple terms, the fate and effects of each drug depend on how each organism "processes" the drug. As different species have different molecular tools (e.g. liver enzymes), they will be more or less sensitive to the effects of drugs. A drug may be beneficial to one species, while at the same dose it may be toxic to another species. Famous examples are paracetamol and chocolate which are toxic (sometimes fatal) to our pets! Here, relatively low doses of diclofenac will cause kidney toxicity in these birds, and eventually visceral and joint gout followed by death. Vultures of the genus Gyps are particularly susceptible.
In India, Pakistan and Nepal, catastrophic declines of vultures occurred in the 1990s. The decline of three Gyps species reached over 96%. It took nearly a decade of scientific investigation to find the cause: diclofenac. Since cattle are sacred there, their meat is not eaten. To let them die without unnecessary suffering, diclofenac was recommended and then used extensively by farmers. What at first seemed like a sound and ethical idea has turned out to be devastating in these countries. To begin with, as there were hardly any vultures left, the carcasses were not disposed of. When the animals died in rivers or other bodies of water, water quality was affected and water sources compromised. Then, other opportunistic scavengers increased their populations. Wild feral dogs are ubiquitous in India, and as the vultures disappeared, they found new food sources and the problem worsened. The increase in wild dog populations has led to an increase in the incidence of zoonotic diseases, such as rabies, which is fatal for any vertebrate animal including human. This is an example of how a single change in the use of a drug (diclofenac in livestock) can ultimately affect the health of humans, animals and ecosystems.
Fortunately, diclofenac was banned in 2006 in India, and nature is resilient, although it takes a long time for vulture populations to return to normal (in some areas they still have not). This is a relatively simple example. In Africa, there are also significant vulture declines, but the reasons are multi-factorial and therefore much more difficult to manage. In Europe, the conservation status depends on the species. Human persecution and lack of food (due to declining farms and land use changes, e.g. urbanisation) have made the survival of vultures very difficult. Most species have been eradicated from entire regions. Griffon vultures are on the increase in the Pyrenees, now that carcasses are left in some places (feeding stations) for them to feed on. It is more difficult for other species, and sometimes careful reintroduction programmes are the only way to get them to live again in certain areas.
A general, but important, consideration is that we must learn from our past mistakes. While the preservation of ecosystems is vital for the survival of our societies, humans are still exerting increasing pressures on the natural world. Now more than ever (despite a small respite due to the COVID-19 lockdowns) and we cannot afford to repeat the same mistakes. There are just too many consequences for animal welfare (diclofenac-induced kidney disease is extremely painful, as any gout human sufferer will tell you), conservation, ecosystem functioning, and human health. In this context, we were quite surprised to see that diclofenac was again allowed in some European and African countries. In Spain, for example, it was authorised as recently as 2013, even though this is the country with the largest vulture populations! The presence of NSAIDs, including diclofenac, has been confirmed in (pig) carcasses at the vulture feeding station. Researchers thought that this could have a dramatic impact on vulture populations, knowing what happened in Asia, and estimated an annual mortality ranging from 78 to 600 individuals for Gyps fulvus. These concerns were unfortunately confirmed by the discovery of a dead cinereous vulture fledgling with visceral and articular gout and confirmed diclofenac intoxication. The species is also classified as near-threatened by the IUCN and has recently been reintroduced to northern Spain. Only 61 individuals were known in 2020. As with any wild species, detecting mortalities is incredibly difficult for vultures, as individuals can reach very remote and inaccessible locations, hide when ill or be consumed or degraded quite quickly after death. Who knows the real impact on European vulture populations, especially for the more sensitive Gyps vulture? All this could have been avoided if the lessons of the past had been learned and stricter regulations had been adopted.