Lessons from Species at the Brink

A group of African White-backed vultures (Gyps africanus) at a carcass in the Sahel of Senegal, West Africa.  The large vulture arriving in the foreground may be a Ruppell's Vulture (Gyps rueppellii).  Photo copyright Richard Telford, 2004.

A group of African White-backed vultures (Gyps africanus) at a carcass in the Sahel of Senegal, West Africa. The large vulture arriving in the foreground may be a Ruppell’s Vulture (Gyps rueppellii). Photo copyright Richard Telford, 2004.

By Richard Telford

In the eighth chapter of her landmark 1962 book Silent Spring, Rachel Carson imagines a world in which no birds sing.  She invokes the catastrophic declines of two iconic birds in American culture to deliver a passionate rebuke of the indiscriminate use of DDT and other insecticides.  She documents precipitous American Robin (Turdus migratorius) and Bald Eagle (Haliaeetus leucocephalus) declines, attributing both to the consumption of prey containing bioaccumulated toxins (earthworms for the robins, fish for the eagles), lowering reproductive capacity, inhibiting embryonic development, and reducing nestling survival.  It is an object lesson in our capacity to alter natural systems, bringing species forcefully to the brink of extinction.  It is an object lesson from which we need to learn more fully:  to react more decisively to such crises and to act more proactively to avoid them when possible.  The response to recent catastrophic Afrotropical (Old World) vulture declines in Asia suggests that such learning is possible.

The long-term implications of vulture population declines in South Asia, as well as Africa, are manifold and complex, and, if they continue at their present rate, the imminent extinctions that follow will produce an equally catastrophic cascade of far-reaching effects, some of which are already evident in areas suffering the worst vulture declines.  A study published in the Proceedings of the National Academy of Science in 2012 noted that in 1997 “>30,000 of the world’s 35,000-50,000 rabies deaths took place in India where feral dog and rat populations have exploded after the decline of vultures.”  While the potential extinction of any species should ring alarm bells, vultures are not simply any species.

While the two groups are phylogenetically and biogeographically distinct, Afrotropical (Old World) and Neotropical (New World) vultures serve an equally critical role in the systems they inhabit.  This parallel role, along with morphological and behavioral similarities, has contributed to the two vulture groups being viewed as the textbook example or classic case of convergent evolution.  The fact that these two groups have evolved to fill precisely the same niche role in distinct natural systems serves to emphasize the unique and critical nature of that role. Vultures are the only known vertebrate terrestrial obligate scavengers.  Such specialization, while providing benefits to a species, likewise makes it highly vulnerable to extinction.  The Gyps genus of vultures, comprised of eight of the sixteen Afrotropical vultures, offers a stark illustration of this vulnerability.

Between 1992 and 2007, the Indian White-rumped Vulture (Gyps bengalensis) experienced a staggering 99.9% population drop in India, a decline directly linked to the veterinary use of the nonsteroidal anti-inflammatory drug diclofenac in livestock treatment, a practice that began in India in 1993.  G. bengalensis likewise experienced a 91% population drop in Nepal between 1995 and 2011, due principally to diclofenac poisoning, and the 1998 introduction of diclofenac in Pakistan caused similarly rapid, massive vulture declines.  The effects of diclofenac on many Afrotropical vultures have subsequently been well documented.  The consumption of diclofenac-tainted carrion leads to rapid renal failure and visceral gout in at least five Gyps species, causing death in as little as 48 hours.  As of this writing, the IUCN lists three Gyps species as critically endangered:  the Indian White-rumped Vulture (G. bengalensis), the Slender-billed Vulture (G. tenuirostris), and the Long-billed Vulture (G. indicus).  All three declines have been causally linked to diclofenac poisoning, and this link, in conjunction with the realization of the potentially catastrophic effects of local vulture population extinctions, has prompted four South Asian countries to ban veterinary use of diclofenac since 2006, a decision lauded by the World Conservation Congress, which noted that “these massive declines of vultures are unequivocally caused primarily by a single human activity and could be reversed.”

The ban on veterinary use of diclofenac instituted by the governments of India, Nepal, and Pakistan in 2006, and Bangladesh in 2010, in conjunction with conservation efforts undertaken by the SAVE (Saving Asian Vultures from Extinction) consortium as well as a large number of NGOs including The Peregrine Fund, The Darwin Initiative, WWF Pakistan, and others, has yielded clear, though modest, success in helping affected vulture populations to recover.  This success has been most notable in Pakistan.  However, much work remains.  The lessons here are many.  Definitive evidence can, for example, prompt decisive action, though no one decisive action can wholly address a complex conservation problem.  This is well illustrated in India where, at the present time, there is concern that diclofenac packaged for human consumption is illicitly being used in veterinary applications, prompting calls for stricter regulation.  Vulture conservation efforts in South Asia also demonstrate the potentially greater efficacy of regional approaches.  Such efforts, however, require significant coordination among governmental agencies, NGOs, and, perhaps most importantly, local constituencies.  Vulture conservation efforts in Africa, for example, have lagged behind those in Asia in part due to the lack of such a coordinated effort.  Additionally, vulture declines in Africa, unlike those in Asia, have not been linked principally to one central cause, making the path to decisive action less clear.

Finally, perhaps the most important lesson of the vulture crisis in Asia is one with which we are too familiar, but it bears repeating.  We have a tremendous capacity to catastrophically disrupt natural systems through fairly isolated actions, such as the introduction of a single non-steroidal anti-inflammatory drug into a bioregional food web.  It is precisely this power that Rachel Carson wrote about in 1962.  The inherent danger in successfully bringing a species back from the brink of extinction in such circumstances lies in the false sense of confidence that such an action can produce:  the belief that, with our technology and know-how, we will always succeed in doing so.  The object lesson here is that failure in some of these efforts is inevitable.  The greater efficacy in conservation efforts lies in being proactive rather than reactive.  As a result of the vulture crisis, there are efforts underway in South Asia to require more thorough testing of all veterinary medicines for their potential ecological effects before being put into use.  Here, too, is reason for hope.  If, as Rachel Carson stated, “the beauty and the ordered world of nature still have a meaning that is deep and imperative,” we must shift our thinking and our actions accordingly.

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In Defense of Vultures

Turkey Vulture Sketch

A sketch from my field journal of a car-struck turkey vulture (Cathartes aura), July 17, 2012.

By Richard Telford

Author’s Note: This is the first in what I anticipate being a long series of posts on the natural history and conservation of vultures. While these posts will likely not follow a rigid order, I hope to eventually meld them into a longer, more substantive work titled In Defense of Vultures.

Epilogue

A light, easterly breeze bent the slender stalks of Queen Anne’s lace and goldenrod that had emerged in early summer from the patchwork quilt of little barley and fescue, overtaking red clover and thistle long past their blooming. Just as the breeze undulated the complex fabric of disturbance obligate plants, so too did life itself undulate there, in short, complex cycles in which plant overtook plant, each bringing an equally complex host of pollinators, predators, migrants, and breeders, all quickly mortal in the short-lived life-burst of the summer pasture.

Such were the observations I recorded on July 22, 2012 as I sat on Lois Cole’s small memorial bench nestled among the trees in Monument Pasture in the Edwin Way Teale Memorial Sanctuary in Hampton, Connecticut. By 1:30 the temperature had reached 80 degrees, and I sat adding species to a master site list while the raucous pasture music in all its forms reached its daily crescendo. Ten minutes later, a shadow at the periphery of my downward gaze drew it upward, first to the brightly lit mass of an old eastern white pine at the pasture’s southeast edge, then across the pasture itself, finally up to the azure sky marked by a scattering of cumulus clouds.

Perhaps thirty feet above, the penumbral form of a turkey vulture (Cathartes aura) drifted in its rocking, dihedral flight, circling the pasture several times before disappearing beyond the tree line. This dihedral flight, in which vultures utilize thermal columns and expend little energy, allows them to outcompete facultative vertebrate scavengers. This evolutionary adaptation is critical for vultures, the only known terrestrial vertebrate obligate scavengers, and thus vultures serve a concomitantly unique systemic role. Vultures increase the energy cycling of natural systems, moving energy stored in carrion quickly through the trophic levels. They likewise serve a critical sanitation function. Despite historic, cultural maligning of vultures as filthy scavengers that spread disease, they in fact check the spread of carrion-based diseases, aided by a number of evolutionary adaptations.  These include exceptionally caustic stomach acid that can break down bacterially toxic carrion, featherless heads that resist the crusting of putrid flesh while feeding, and, in the case of the turkey vulture, acutely sensitive olfaction that will prompt rejection of the most toxic remains.

These and many other adaptations, some of which will be examined in subsequent posts, confer a unique ecological role upon the turkey vulture in particular and on the other 21 extant vulture species worldwide more broadly. Such niche roles necessarily create a duality for the species that fill them; while these species are especially critical to systemic function, they are also highly prone to extinction when the systems they occupy are disrupted. Such vulnerability is illustrated by precipitous population declines in the Gyps genus group in Asia and Africa, due principally to poisoning from livestock carcasses containing diclofenac, a commonly prescribed veterinary non-steroidal anti-inflammatory drug which causes rapid renal failure in exposed Gyps vultures. The Oriental white-backed vulture (Gyps bengalensis), for example, has suffered a staggering 99.9% population decline in India. These potentially catastrophic vulture losses will be examined more closely in a later post.

I focused little on the natural history or conservation of vultures on that warm July day. Instead, in my journal I noted the “low, lumbering flight, riding along warm air currents, still-winged and seemingly motionless.” The vulture was, I felt (and still feel), “an apt metaphor” for life, showing us the importance of “embracing life’s currents; changing direction by slow, deliberate degrees; conforming to the world’s parameters rather than trying to force the world to conform to our desired ones.” I concluded my observations by writing one simple word loaded with complex implications: “Magnificent.” Here was an illustration of the way in which scientific observation and emotional response cannot be fully separated, despite traditional calls for objectivity. In observing natural systems, how can we help but see ourselves, even if only through stark contrasts of what we may have been millennia ago, are at present, and may be in the future? Without such connections, how can we avert what Richard Leakey, Roger Lewin, Niles Eldredge, and others have termed the sixth extinction?

Five days after my initial turkey vulture observation at Monument Pasture, a shadow at the periphery of my gaze once again drew my attention. Driving home on state route 97, having finished a long morning of observations at Monument Pasture, a dark shape in the summer weeds at the road edge drew my gaze. A large wing rose up as I passed, and I could see the distinct, articulated wingtip feathers of a turkey vulture, likely car-struck. I pulled my car to the shoulder and walked heavy-heartedly back towards the vulture, its wings periodically unfurling, cutting the hot, dry air with the sound of delicate paper crumpling. I was distressed by the obvious suffering of an animal that, five days earlier, had evoked in me the deepest awe. I wondered if this could be the very animal that, days earlier, had silently circled Monument Pasture.

Reaching the vulture, I realized it was already dead; its bluish eyelid was drawn tight, a small heart-shaped pool of blood darkened the ground near its beak, its frame neither expanded nor contracted with breath. The light, broad wings that in life had allowed its effortless soaring now caught even the slightest breeze, drawing the splayed bird upward by inches only to drop it again like a downed kite. I quickly rough-sketched the vulture in its entirety, first feeling grief, then wonder, then gratitude. Realizing the gift of observation that this vulture had unwittingly given me through its death, I knelt beside it for another ninety minutes, painstakingly sketching its head, seeing the beauty of its graceful flight mirrored in the complex beauty of its functional adaptations. Gazing at this young vulture’s hooked, tearing beak, its bald head that would resist the caking of putrid flesh as feathers could not, its large, open nostril through which the ground beneath it was visible, it was clear to me why Thoreau, 158 years earlier in Walden, had written, “We are cheered when we observe the vulture feeding on the carrion which disgusts and disheartens us, and deriving health and strength from the repast.” If we wish to avert the sixth extinction, perhaps the beauty of function must be invoked to foster conservation-mindedness as readily as the beauty of form.