In Africa, the response of some vulture populations suggests how climate change may directly affect birds in their mountain refuges.
Many vulture populations are already declining in the face of a range of human threats, prominent among them poisoning via carcasses treated by African livestock herders, who actually intend to target predators such as jackals, lions and hyenas. Feeding havens known as vulture “restaurants” have been created as a conservation response, to provide these large scavengers with regular, safe, but artificial food sources including wild and domestic animal carcasses.
Despite such measures, mountain vulture declines have continued. Some authorities, while not discounting the impacts of poisoning, are questioning whether climate change may have a role in declines of two large mountain vulture species found in southern Africa, namely the cape vulture, Gyps coprotheres, and bearded vulture, Gypaetus barbatus.
The continent’s largest raptor, the cape vulture is a vulnerable endemic species found only around cliffs in southern Africa. It nests mostly at higher altitudes on south facing cliffs, an orientation that provides for cooler conditions. At lower elevations they may also use coastal cliffs benefiting from cool ocean breezes. As for bearded vultures, these large mountain birds have almost three-metre wingspans and, unusually for vultures, feathered heads. They are endangered in Europe and South Africa but are also found in other African mountain regions and the Himalayas. Mentioned in the Christian bible as the ossifrage, or bone breaker, this bird allows other scavengers to consume fleshy carcass remains, then flies off with the bones to its lofty ossuaries. There it stores the bones, which it will later prepare for eating by dropping them from a height to break, before spiralling down to reclaim the pieces.
Patterns of decline in some cape and bearded vulture populations, it is thought, are consistent with climate change, according to Rob Simmons and Andrew Jenkins of the University of Cape Town. The two northernmost (low latitude) cape vulture colonies, in Namibia and Zimbabwe, have become extinct as breeding colonies, despite in Namibia’s case a feeding program aiming to prevent this. The only cape vulture colony currently expanding is at the southern (pole-ward) extreme of this bird’s range, on the western Cape of Africa (also the site of a vulture restaurant). To the northwest, around Lesotho, both cape and bearded vulture breeding sites at lower elevations have disappeared, and their ranges are contracting to the Lesotho highlands. At the equator, Kenya’s only known bearded vulture population has become extinct and reintroduction efforts have failed; although other direct human factors cannot be ruled out, this would be the first population expected to become extinct under climate change, Simmons and Jenkins say.
That these range contractions and local extinctions are consistent with climatic warming over the vultures’ ranges suggests that climate change could be the “elephant in the room” that “may be the real culprit in the demise of our charismatic vultures,” write Simmons and Jenkins. The mechanism, it is speculated, could be vultures’ physiological intolerance of hotter temperatures because, “A montane-adapted vulture sweating it on a baking cliff face has few other options than to move to another location, ” write Simmons and Jenkins. Another theory is that carbon dioxide levels may promote bush encroachment, and bushier landscapes reduce the efficiency with which vultures can find food, another factor that could be helping to push Namibia’s cape vultures out of existence.
Although largely speculative in this case, understanding the possible role of climate warming and greenhouse gases would inform vulture conservation efforts. It might suggest, for example, whether attempts to re-introduce vultures should focus on sites at the highest altitudes, where birds would likely withstand warming for longer. Vultures, as highly-specialised scavengers, have an important role in quickly disposing of large animal carcasses, indirectly benefitting human health. In India, a crash in vulture numbers and concomitant explosion in feral dog and rat populations coincided with tens of thousands of human deaths from rabies.
Simmons R.E., Jenkins A.R. (2007) Is climate change responsible for the demise of the Cape Vulture and Bearded Vulture in southern Africa? Vulture News 56:41-51.
Sekercioglu C.H., Daily G.C. & Ehrlich P.R. (2004) Ecosystem consequences of bird declines. Proceedings of the National Academy of Sciences. 101(52): 18042-18047