Many vultures face imminent extinction across Africa, Asia and parts of Europe, where vulture populations are in freefall. The IUCN Red List charts a relentless decline over recent years. In 1994, 75% of the world’s 16 Old World vulture species were classified as Least Concern, meaning that they were not considered at risk of extinction. Only one species—Cape Vulture Gyps coprotheres—was thought to be globally threatened and was classified as Vulnerable. Today, just two species remain Least Concern. Of the rest, eight, half of all species, are classified as Critically Endangered and are at risk of imminent extinction; three are almost as imperilled and are classified as Endangered; and three are Near Threatened.
Populations in South Asia were the first to collapse, with declines of around 95% between 1993 and 2000. These were principally the result of acute poisoning linked to livestock carcases contaminated with the veterinary drug diclofenac. Worryingly, vultures are also disappearing across vast swathes of Africa. Over a period of just 30 years, populations of seven African vulture species have fallen by 80-97%. Here, the threats are more varied. They include deliberate persecution, such as by elephant poachers who kill vultures so that they do not draw attention to their illegal activities. Vultures are also killed for their body parts, which are traded for their supposed mystical properties. Other threats include habitat loss and degradation, decreasing food availability, fragmentation of remaining populations, human disturbance, collisions with wind turbines and powerlines, and electrocution on electricity infrastructure.
These disturbing statistics provide a place from which to discuss the complexities of wildlife conservation and convergent evolution.
The vultures are divided into two broad groups; the Old World (Europe, Asia, Africa) and the New World (American) Vultures. Even though they have a number of similar adaptations (see list below) they belong to different families of birds. Old World Vultures belong to to Accipitridae (the raptors) and New World Vultures belong to the Cathartidae. The similarity in morphology is an example of convergent evolution rather than descent.
Common adaptations in Old and New World Vultures (from Wink, 1995, Ogada etal, 2011)
- bare heads and necks avoid pollution of feathers when feeding inside a carcass
- strong hooked beaks with cutting edges to tear skin apart
- long intestine and a stomach with strong acid are suitable for the digestion of rotten meat and bones and furthermore the latter kills microorganisms present in the putrified carrion
- the broad wings enable them to ride rising air currents with little energy expenditure while scanning large areas for carcasses
- aerial searching also gives vultures a considerable advantage over terrestrial scavengers because the latter have limited feeding ranges, higher energy expenditures to locate carcasses, and comparatively poor visibility from the ground
- the feet of vultures are more appropriate for movement on the ground than to catch prey (as in other raptors)
- excellent eyesight which enables them to detect carcasses from great heights. (New World vultures also have a well developed sense of smell that is used for locating food in forested areas.)
Vultures play an important ecological role by consuming carcasses. Outside of the oceans, vultures are the only known obligate scavengers (Ogada etal, 2011).Their strong stomach acid kills microorganisms in carcasses that may kill other scavengers or turn them into vectors for diseases such as anthrax, botulinum toxins, rabies, and hog cholera (World Atlas). Removal of vultures from an ecosystem increases the disease risk posed by these microorganisms.
Poisoning Grys vultures in Asia.
Following the cessation of its patent in the early 1990s, the NSAID (non-steroidal anti-inflammatory drug) diclofenac became widely available in India, including for veterinary use. It is also used in humans for treatment of arthritis, although it is perhaps better known as Voltarin. The drug causes kidney failure in vultures of the Grys genus, (specifically severe, acute, renal tubular necrosis and resultant uric acid crystal deposition in the kidneys and other tissues.) In laboratory studies death occurs in less than sixty hours. What functions as medicine (albeit with complications) in mammals functions as a poison for the Grys genus vultures; a poison that resulted in a 95% reduction in the population of three species of Indian vulture in less than a decade.
White-backed and long-billed vultures were once regarded as probably the most common large raptors in the world but, in about a decade, and with a total loss estimated at tens of millions of individuals, these birds were listed as critically endangered. (Oaks, 2012)
Wikipedia has a page entitled the Indian Vulture Crisis which is worth a read. I have attempted to diagram the flow on effects of this species decline below. The emergent cost on human populations is enormous.
Poisoning African Vultures
Many species use vultures as a carcass detection services, e.g. hyenas and other vultures. But for Africa’s big game poachers this environmental service also functions as a poacher detection service, therefore some poachers have been deliberately poisoning carcasses to prevent the vultures giving away their location. A widely reported incident in 2019 resulted in the death of over 500 vultures from the poisoning of just three elephant carcasses in Botswana.
The 'Point of Wonder' for me in this is that it requires so few links to go from providing an anti-inflammatory drug to cows to leopard predation of humans, or from the same starting point to significant interruption of a religion. The intermediary step in this chain is a particular group of birds, the vultures.
