Vultures are an essential group of scavengers that clear the land of dead animals, but human practices may be putting them, and ultimately us, at risk.
Vultures are inadvertently being poisoned by eating animals that are loaded with antibiotics.
Photo by Mattiaath/Fotolia
Peter Doherty is a Nobel Prize-winning Immunologist, whose research points to the special role avian animals play in the environment at large. In his book Their Fate is Our Fate: How Birds Foretell Threats To Our Health and Our World (The Experiment Publishing, 2013), Doherty explains how human practices are impacting vultures and the unintended consequences that come from their population decline.
Vultures are not particularly lovable birds, and they don’t generally receive much favourable press. The cartoon image that comes to mind is of the guy crawling in the desert, tongue hanging out, no water in sight, while a couple of bald-headed, gloating vultures perch close by waiting for his final collapse and loss of consciousness.
But the fact of the matter is that vultures are, like the much more highly regarded bald eagles, essential scavengers that clean our landscapes. In Africa they share that role with some mammals, particularly the hyenas, though to be called a hyena is no more of a compliment than to be described as a vulture. The African vultures, and no doubt the hyenas, are thought to have coevolved with ungulates like the buffalo, wildebeest, springbok, giraffe and zebra. As the human population continues to expand, these native herbivores progressively lose habitat, and more and more are killed to provide ‘bush meat’. Some species (particularly wildebeest and buffalo) are now farmed, but with directed harvesting and management, many fewer will fall to lie in the field. The inevitable consequence is a decrease in vulture counts everywhere but in the well-monitored wildlife parks where the natural cycle of life and death is rigorously maintained. In addition, being big birds like the bald eagles, vultures tend to fly into high-tension wires and other obstacles that we place around the landscape.
The African bearded vulture is classified as endangered, while the more common white-backed vulture has been put in the near-threatened category by the International Union for the Conservation of Nature (IUCN). Overall, though, the situation of vultures is much more dire in India, Nepal and Pakistan. The IUCN’s red-list category identifies the three species of Indian vulture as critically endangered, a situation that has developed with enormous speed over the past 20 years or so. Apart from threatening the birds themselves, this is also an extremely serious situation for the extensive rural populations of these countries. There are no hyenas on what is generally known as the Indian subcontinent, but there are many cattle, which are, partly for religious reasons, often left to die naturally. The vultures have traditionally provided a completely free and very efficient sanitation service.
As recently as 1992, there were vultures everywhere in the rural areas of the subcontinent. Then, before that decade was out, the numbers fell very rapidly. Both concerned individuals and local authorities started to look closely, and a number of US groups, like the Peregrine Fund based in Boise, Idaho, and the Washington State University Veterinary School at Pullman, quickly became involved. Dead birds were collected, preferably close to the time of their demise — that part of the world tends to be pretty hot on the whole, and as I learnt in my early days as a veterinary scientist, the fresher the better when it comes to doing a detailed post-mortem.
The investigating pathologists quickly established that once the usual causes of avian exit were excluded, otherwise healthy vultures were dying acutely of visceral gout. Gout? For most of us that evokes the image of some testy, bibulous, red-nosed old duffer with his painful, swathed foot and ankle parked on a cushioned footstool. Vultures aren’t likely to imbibe copious quantities of port and red table wine, so what could be happening here? Well, human gout is caused by the accumulation of needle-like uric acid crystals in joint tissues and blood capillaries. The ultimate breakdown product of the purines found in many foods, uric acid is normally excreted via our kidneys. Conditions associated with progressively compromised kidney function, like hypertension and diabetes, predispose to gout. If there’s no underlying genetic or other medical cause, gout may be more a consequence of a long-term over-indulgent, low-exercise lifestyle characterised by the excessive consumption of red meat and salt. Drinking a lot of good (or bad) wine can go with that, but alcohol may not be a primary cause. And even abstemious vegetarians aren’t totally protected, as an excess intake of fructose is also a risk factor.
Birds and humans share the characteristic of not having a functioning urate oxidase (uricase), the enzyme that breaks down uric acid. It’s true that vultures do go for the red meat bit, but they also get plenty of exercise and they’ve consumed that diet through evolutionary time without having a notable gout problem. Also, the dead Indian birds had visceral gout, meaning the uric acid crystals were so widely distributed that the organs looked white when the pathologist opened the body cavity. Of course, all birds excrete a concentrated white paste of uric acid rather than the dilute solution of urea (and some uric acid) that is characteristically found in mammalian urine. The presence of uric acid all over the place immediately suggested that some form of kidney damage must have been responsible for the vulture wipeout.
Given the acuteness and wide territorial distribution of the problem, the first thought was that the vulture deaths might have been caused by a novel infection. Working with investigators in Pakistan and India, the Washington State microbiologist Lindsay Oaks and Scots veterinarian Martin Gilbert took on the task of exploring this possibility, but they could not identify a causative virus, fungus or bacterium. Samples were also sent to the ultra– high security Australian Animal Health Laboratory (AAHL) inGeelong, about an hour’s drive from Melbourne. The AAHL virologists really know their stuff, and they did find a new herpes virus, but though there were concerns that this could prove a problem for captive vulture breeding programs, it was clearly not inducing the visceral gout problem.
Failing to identify an infectious cause, Oaks, Gilbert and Peregrine Fund biologist Munir Virani reasoned that dead domestic livestock were a major food source for the affected vultures. Could the cause be something that was being given to the cattle? They checked out the veterinary drugs that were currently in widespread use, focusing on those that were relatively new to the market and that might be expected to cause some degree of renal toxicity. That led them to the non-steroidal anti-inflammatory drug (NSAID) diclofenac (Voltaren). Oaks tested his samples and found that all those from birds with visceral gout contained diclofenac at some level, while the ‘control’ tissues from an equivalent number of gout-free vultures were uniformly negative. Their report appeared in the leading science journal Nature in 2004. (Even the world’s top scientists break out the champagne if they get a paper published in Nature, and what editor could resist a great vulture detective story?)
Where was the drug coming from? Diclofenac is out of patent, is very cheap, and was being made by a number of Indian manufacturers. Though cattle enjoy a particular status in Hindu culture, they are nevertheless put to productive use. Loads of the drug were being given as a broad-spectrum treatment for general inflammatory conditions and malaise. Draft oxen (castrated cattle) are still very important to the rural economy, and treatment with diclofenac meant that those with sore joints could soon go back to work. It was also used to restore milking cows to production. And though they are not to be killed, it is acceptable to provide some treatment for cattle that are roaming free and obviously suffering. Many such animals are grossly compromised, not least because of the ingestion of plastic bags — cows are not picky eaters.
There’s so much happening in science, and most of us are far too busy. Having missed the Nature paper by Oaks and his colleagues and the excellent overviews written by Susan McGrath and others, I was, in fact, completely unaware of the vulture story until I made a 2009 visit to the University of Pretoria’s Veterinary School in South Africa. I was there at the invitation of the Dean, Gerry Swan, to give the Sir Arnold Theiler Memorial Lecture. This was an offer that could not be refused. Arnold Theiler — the father of Max Theiler, the yellow fever vaccine pioneer whom we met in Chapter 4 —i s a genuine hero of infectious disease research.
During my visit, I got to talk science at length with Gerry and with a number of the senior faculty members. Hearing about what’s happening with animal diseases, particularly those that don’t transmit to humans, is often fresh and interesting, as I’m pretty much embedded in a basic biomedical research culture. My discussion with Gerry and his close colleague and protégé Vinny Naidoo was my introduction to the Indian vulture story.
Gerry is a pharmacologist who returned to academia after spending some years working for what was then Merck & Co. His expertise in drug research, together with the certainty that the African white-backed and griffon vultures were not experiencing the visceral gout problem, made him an ideal person to look further at the diclofenac issue. Responding to a request from Mark Anderson of the Endangered Wildlife Trust’s Vulture Study Group, Gerry and his research group soon reproduced the characteristic visceral gout pathology by dosing African vultures with diclofenac.
Using the African white-backed vultures, Swan, Naidoo and their colleagues were then able to show very quickly that an alternative and equally inexpensive anti-inflammatory, meloxicam, could be used in cattle without causing any problem for the big birds. Even with this breakthrough, though, and with the Indian and Pakistani governments imposing a total ban, it’s been very hard to get the message out and to remove all the diclofenac from the farms and veterinary supply houses. In addition, another NSAID, ketoprofen, has come into the picture and is just as toxic as diclofenac.
These are good drugs so far as cattle are concerned, but when any therapeutic is given as a broad-spectrum, symptomatic treatment to large numbers of animals in the field, it is inevitable that a few will die from some underlying, and often undiagnosed, cause. Hundreds of vultures can be observed to feed on a single dead cow. According to the mathematical ecologists, the massive, rapid decline in the Indian vulture populations could be accounted for by as few as one in every 760 cattle carcasses having substantial levels of diclofenac.
How does the drug kill? Like many toxins and therapeutics, it concentrates in the liver, which is like pâté de foie gras to a hungry vulture. The mode of action is still controversial, and I won’t confuse you and possibly myself by discussing the likely mechanisms in any depth. Suffice it to say that there is damage to (necrosis of) the sensitive, proximal, convoluted kidney tubules, which could be a consequence of diminished blood flow and/or the effect of those terrible free radicals we hear so much about in advertising blurbs for non-prescription medications. Whatever the final cause, the resultant failure to clear uric acid via the kidney leads to its rapid, lethal accumulation in tissues. This in turn causes excessive potassium build-up in the blood and terminal organ failure.
The principal consequence of the die-off in the vulture populations is, of course, the loss of a free and efficient environmental sanitary service. The net result is greater food availability for other carrion-eaters. Wild dogs, which are both abundant in India and the main carriers of rabies, increased dramatically in numbers. As a consequence the risk of dog-bite also went up for rural workers, with a 2008 estimate suggesting that the loss of the vultures led to 50 000 excess human deaths in India alone. Rabies is a horrible way to die. There is the possibility of post-exposure treatment, but cost, limited medical access and the lack of education that causes poor farmers to opt for ‘traditional’ remedies means that being bitten by a rabid dog is too often a death sentence. Aggressive programs to cull or sterilise dogs that are not properly controlled are leading to substantial mitigation of this problem.
But the loss of the vultures also has cultural repercussions. The Parsi have long followed a very reasonable practice of putting their dismembered dead out on stone ‘towers of silence’ to be stripped by vultures. No vultures means no corpse removal. Also, as India becomes increasingly prosperous and more people take the spectrum of pills that are already ingested by the elderly in Western societies, one wonders what other drugs may prove toxic for avian carrion-eaters. Though the Parsi practice has the great advantages of not taking up the available land and causing no greenhouse gas emissions, maybe it’s time to consider another approach.
Other birds, like the corvids, are also susceptible to the toxic effects of the NSAIDS, and that characteristic visceral gout must now be on the watch list for veterinary and wildlife pathologists everywhere. One way or another, we are putting enormous amounts of potentially toxic materials into the natural environment while making no effort to assess the possible effects on wildlife and other species. NSAIDS like ibuprofen are, for example, also toxic for dogs. Dogs and vultures are very visible, but what of the myriad other animals that inhabit our world?
When it comes to toxins, their detection generally depends on access to appropriate laboratory services, another reason why, if we see significant numbers of dead birds (or other wildlife) it is important to get their remains to state health laboratories. Poisoned seed has been used to kill birds that are regarded as pests, but how can anyone believe that such products will not also be lethal for other avian species?
If we do take the trouble to pick up dead wildlife, though, it is important to be careful and protect ourselves against possible infection. Also, as rabies can be endemic in species like foxes and raccoons, there needs to be absolute certainty that the animal is not still alive before approaching too closely. Rabies is not a problem with birds, though fruit bats carry closely related lyssaviruses that can be just as lethal. Sick bats should only be approached by licensed bat handlers.
Despite their bad public image, vultures have become a matter of grave concern for those interested in avian conservation and the health of natural ecosystems. The Mumbai Parsi are embarking on a vulture-breeding program to deal with the problem that they have been facing in disposing of their dead. And there is great concern about the long-term future of those great American vultures, the condors. For instance, a March 2013 advertisement is calling for ‘volunteer field biologists’ to work in an Ecuadorean conservation project that is ‘a collaboration between Fundación Galo Plaza Lasso, the Community of Zuleta and Fundación Zoológica del Ecuador (the parent organization of Quito Zoo), and is part of Ecuador’s National Strategy for Conservation of the Andean Condor.’ It is believed that there are less than 50 wild condors left in Ecuador. If you’re young, know some biology and have a little time to spare, that could be the path to a very interesting future, or at least the material for some very good stories as you grow older.
The wildlife organizations tend to feature spectacular animals in their publicity and vultures don’t, for obvious reasons, normally figure in TV ads and the like. But every life form is important, and different people can be obsessed by all sorts of creatures that may have little public appeal. Apart from his Galapagos Finches, Charles Darwin of evolution fame spent a decade dissecting and analysing barnacles. There’s a story that when one of Darwin’s sons was playing with a neighbor’s boy, he asked his friend: ‘Where does your father do his barnacles?’ Birds are much easier to see in nature, which is part of the reason that passionate volunteers are able to contribute so much to the science. Observing small mammals, say, can require the careful positioning of fixed cameras, an expensive procedure that requires a good deal of scientific insight.
The following is taken directly from the description of the Audubon Society’s annual and long-running Christmas Bird Count: Each of the citizen scientists who annually braves snow, wind, or rain, to take part in the Christmas Bird Count makes an enormous contribution to conservation. Audubon and other organizations use data collected in this longest running wildlife census to assess the health of bird populations — and to help guide conservation action.
What is so important here is that the birders are not just recording numbers and sightings for spectacular birds, but are also providing the data on what’s happening with more modest species. Then there’s the 4-day ‘Backyard Bird Count’, led by the Cornell Lab of Ornithology and the National Audubon Society, with Canadian partner Bird Studies Canada and sponsorship from Wild Birds Unlimited.
If recording bird species and numbers (particularly in midwinter) isn’t your thing, think about the July 4 national butterfly count of the North American Butterfly Association, with similar events around the same time in both Canada and Mexico. Just go online, and you will find the instructions on how to set this up so that you can contribute information to a national database. Like the birds, many species of butterfly are moving away from the equator, or up to higher altitudes, as the planet continues to warm. Minimising the use of chemical insecticides also protects butterflies, though large numbers of butterflies are killed by cars and trucks and (apart from driving less) there’s not a whole lot we can do about that.
We normally invoke the ‘birds and the bees’ in a different context, but it’s also the case that a broad spectrum of people, from apiarists, to agriculturalists, to environmental scientists and so forth, are very concerned about what’s happening with the bees. Like many birds, bees are of major importance when it comes to pollinating plants, including those that feed us. Again, issues like insecticide use and climate change are major concerns. There’s a statement from the British Royal Horticultural Society that describes what is clearly a global problem: Beekeepers and gardeners have noticed that bees are less healthy and abundant in recent years than they have been in the past. If this trend continues, it could have serious implications, since most plants rely on bees and other insects to transfer pollen from one flower to another in order to set fruits and seeds.
That is happening globally. Maybe the ‘birds and the bees’ do not, as the myth is said to go, make babies, but their busy work, being so important for both food production and the wellbeing of natural ecosystems, does promote both our physical and psychological health.
Excerpted from Their Fate is Our Fate: How Birds Foretell Threats To Our Health and Our World, © Peter Doherty, 2013. Reprinted by permission of the publisher, The Experiment.
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