Rochester-Abby Frawley (SEAL President)- 3/21/2017
Research Paper for Conservation Biology (BIOL 475) Spring 2016
When a cow dies in India, a very particular group of funeral crashers arrives on the scene to mourn. They’re the worst kind of guests, more interested in dining than in the deceased; worse still, they arrive in a mob and turn a wake into a banquet.
But these piggish pallbearers serve an important purpose too. Vultures—the birds that even Charles Darwin was revolted by when he saw one circling over the deck of the Beagle—are nature’s most elegant scavengers. With wings built for gliding and keen eyesight, vultures can quickly locate carrion and efficiently stalk herds in search of their next meal, and when it’s time to eat, the high acidity of their digestive tracts allows them to destroy any microbes that may have grown on the corpse, thereby reducing the spread of disease. In short, they’re nature’s most effective sanitation crew, a boon for the health of humans and ecosystems alike, ghastly gobblers who prevent corpses from lingering on the landscape. It’s difficult to quantify and track the benefits of what vultures do when their populations are healthy but, more and more, vulture populations are dwindling, and the importance of their job is becoming jarringly clear.
The decline of vultures was first noted in the Indian subcontinent in the 1990’s. Between 2000 and 2002, J. Lindsey Oaks, a scientist with the Peregrine Fund, and his co-collaborators performed autopsies on the recovered corpses of Oriental white-backed vultures to determine what was causing the die-off. They discovered that the birds had died of renal failure caused by gout, and that the death had been sudden—none of the vultures had suffered from a chronic kidney condition. Their evidence pointed towards poisoning, which had been common in Africa for years.
The scientists then did a survey of potentially toxic materials among the dead birds, but found that none of the vultures that had died of renal failure tested positive for any known toxic substances. They then broadened their scope and considered other factors that could have led to the poisonings. The primary food source of white-backed vultures in the Indian subcontinent is dead cattle, and so they theorized that the vultures had ingested a veterinary drug. After surveying veterinarians in Pakistan, they narrowed the potential toxins down to diclofenac, a non-steroidal anti-inflammatory drug (NSAID). In the United States, diclofenac is commonly prescribed to humans to manage the pain associated with arthritis and other conditions. In Asia, it doubles as a veterinary drug that’s commonly prescribed to cattle as a cheap way to manage lameness.
The biologists performed another round of tests that revealed that each of the 25 vultures that had died of renal failure had diclofenac residue in their kidneys. Further tests in which captive vultures were given oral doses of the drug confirmed that the ingestion of diclofenac could kill a vulture within days—Oaks and co. saw their subjects die as soon as 36 hours after eating the drug. As more research was conducted, more scientists reported similar findings and began to call for diclofenac to be banned from veterinary use.
While diclofenac was identified by many as the sole cause of the rapid declines of vultures populations, the solution wouldn’t be as simple as banning the drug. The general life history of vultures makes them particularly vulnerable to this sort of event; the raptors have a low reproductive rate and take a long time to mature compared to other birds. Though banning the drug would reduce the deaths, the populations would take years to recover.
And unfortunately for vultures, a ban on diclofenac didn’t come fast enough to stem the losses. A paper published in 2007 found that populations of Oriental white-backed vultures in central and northern India had declined 99.9% in the period from 1992-2007; the same paper estimated that the long-billed vulture suffered a loss of 96.8% of its original populations during the same span of time. In some regions of India, vultures became functionally extinct, meaning that the population could no longer perform the vital services it once used to. Vultures remained on the landscape, but their numbers had dwindled to a level where they no longer had an impact.
With the breeding population of adult vultures swiftly plummeting, the reproductive success of the birds declined as well. In a 2006 study, a team of researchers couldn’t find a single viable nest at one of their Pakistan survey sites, a colony that had once hosted nearly 200 nests. Other sites had significant declines as well; one, for example, had lost over half of the nests it had once boasted by 2003.
In 2006, as more and more research was published about the decline—and more biologists began to single out diclofenac as the sole cause—the Indian, Nepalese, and Pakistani governments placed a ban on the sale and manufacture of the drug and instead began to promote the use of meloxicam, an alternative NSAID proven to be safe for vultures. In the coming years, the amount of carcasses infused with diclofenac would decrease by 50%.
Though diclofenac was banned, the losses didn’t stop; the decline of Oriental white-backed vultures has been estimated to be continuing at 18% per year. While the illegal use of human diclofenac and the importation of the drug from other countries may play a role in the continuing loss of vultures, more important was the decimation of the population to a level that will make it difficult for it to recover. Some studies have begun to put forward that populations are stabilizing—but a 2012 study also pointed out that the scarcity of vultures makes population surveys prone to error, and cautions that survey results may be inaccurate.
These declines—and the consequences that arrive with them—aren’t limited to Asia. In 2013, Spain approved the use of diclofenac-containing products for veterinary use, a controversial decision that led many raptor biologists to call for the European Union to step in and ban the drug. And in Africa, vulture populations are collapsing due partially to them eating poisoned corpses meant for lions and other predators.
The events that unfolded in India and Pakistan provide a cautionary tale about the vital role of vultures in the landscape, illustrating through disease that the loss of vulture populations has detrimental impacts on ecosystems worldwide. Vultures, being obligate scavengers, are the most effective creature known when it comes to cleaning corpses, capable of completely removing the flesh from the skeleton. As vulture populations decline, the amount of carrion on the landscape increases due to incomplete disposal and a shortage of scavengers. This in turn leads to environmental pollution as carcasses rot; in particular, rotting carrion pollutes waterways, therefore decreasing available clean drinking water for humans and animals alike and promoting the spread of disease.
Additionally, other organisms begin to fill the role that the vultures no longer can, which leads to shifts in community structure. In particular, a 2012 paper noted that the loss of vultures leads to more mammal species coming into contact at corpses, which leads to the spread of disease between species and individuals. Both the increased availability of carrion for scavenger species and the spread of disease between populations has the potential to lead to population fluxes that further alter the interactions between ecological communities.
Particularly in India, feral dogs often rise to fill the role that the vultures once held. As the populations of feral dogs increase, so do dog bites, which cause rabies incidences to skyrocket. India in particular already sees 36% of the world’s rabies deaths each year, with most of the victims being under 15 years old. This number is projected to increase as vulture populations continue to plummet. The increase in the dog population, along with the increase in the number of both rabies cases, has been projected to cost the Indian government $1.5 billion annually when one considers the costs of visiting a doctor and paying for a vaccine, along with the cost of human life.
Furthermore, vultures eat carrion before it can become a breeding ground for bacteria and infectious diseases and prevent these toxins from seeping into waterways and soil. In particular, vultures help to minimize the spread of anthrax by quickly ingesting carrion and preventing human contact with rotting meat. Markandya et al. also note that vultures reduce the spread of livestock diseases such as tuberculosis and brucellosis, therefore preventing the loss of livestock and human life.
While we may not think of vultures as being particularly beneficial to us as humans—and yes, we may even the route of Darwin and mock the unsightly mismatch of their bald heads and ragged, feathered napes—it’s important to recognize the often unseen benefits of their presence on the landscape. Vulture conservation is a worthwhile endeavor that’s valued in Nepal at $6.9 million dollars; rescuing vultures will reduce the spread of disease and prevent the loss of human lives, money, and productivity.
A vital component of revitalizing Asia’s vulture populations will likely be captive breeding programs that will allow birds to be raised to maturity and then released back into the environment. The Indian government already supports a captive breeding plan; it will be vital for other countries to adopt similar programs in order to help raptor populations recover. The process of restoring the population to its previous ubiquity will likely be slow and rely on the cooperation of different governments in order to ensure diclofenac remains out of the environment, but will help ensure the health of environments and communities.
After all, if there are no vultures, then who will attend the scavenger’s funeral?
BirdLife International (2013) Vultures are under threat from the veterinary drug diclofenac. Retrieved from http://www.birdlife.org/datazone/sowb/casestudy/156.
Cressy, D. (2014, October 16). Poisoned vulture could herald European bird crisis. Nature. Retrieved from http://www.nature.com/news/poisoned-vulture-could-herald-european- bird-crisis-1.16161.
Gilbert, M. et al. (2006). Rapid population declines and mortality clusters in three Oriental whitebacked vulture Gyps bengalensis colonies in Pakistan due to diclofenac poisoning. Oryx, 40(4), 388-399.
Green, R. E., et al. (2004). Diclofenac poisoning as a cause of vulture population declines across the Indian subcontinent. Journal of Applied Ecology, 41(5), 793-800.
Green, R. E., et al. (2007). Rate of decline of the Oriental white-backed vulture population in India estimated from a survey of diclofenac residues in carcasses of ungulates. PLOS ONE, 2(8), e686.
Markandya, A., et al. (2008). Counting the cost of vulture decline—An appraisal of the human health and other benefits of vultures in India. Ecological Economics, Volume 67(2), 194-204.
McCall, M. (2015, July 1). Why Africa’s Vultures Are “Collapsing Toward Extinction”. National Geographic. Retrieved from http://news.nationalgeographic.com/2015/07/150731-vultures-africa-birds-animals- science/
Oaks, J. L., Gilbert, M., Virani, M. Z., Watson, R. T., & al, e. (2004). Diclofenac residues as the cause of vulture population decline in pakistan. Nature, 427(6975), 630-3.
Ogada, D. L., Keesing, F. and Murani, V. Z. (2011). Dropping dead: causes and consequences of vulture population declines worldwide. Annals of the New York Academy of Sciences, 1249, 57-71.
Prakash, V. et al. (2012). The Population decline of Gyps vultures in India and Nepal has slowed since veterinary use of diclofenac was banned. PLOS ONE.
Ravindran, S. (2013, September 1). Vultures Face Extinction and Indifference. Scientific American. Retrieved from http://www.scientificamerican.com/article/vultures-face- extinction-and-indifference/