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.