Saving An Ark: an Endemics Hotspot in East Africa
By David S. Wilcove, Photograph by Norbert Cordeiro
July 15, 2012
In 2000, Norman Myers and colleagues published one of the most influential papers in conservation biology. Entitled “Biodiversity Hotspots for Conservation Priorities,” it identified 25 areas around the globe that harbored exceptionally high numbers of endemic species (i.e., species restricted to a given area) yet had also been massively altered by human activities. These were places where logging, farming, and other activities had eliminated three-quarters or more of the natural vegetation, placing many of the endemic species within them at risk of extinction. The authors noted that what people “do (or do not do) within the next few decades [to these places] will determine the long-term future of a vital feature of the biosphere, its abundance and diversity of species.”
The Myers team used vascular plants as the basis for delineating the hotspots. Yet virtually all of the places they identified— Madagascar, the Caribbean, Brazil’s Atlantic forest region, and more—harbor endemic birds, too. That is because the history of geographical isolation that typically causes a particular group, say plants, in a given location to diverge into new and endemic species often fosters the divergence of other groups, such as birds.
However, not all of these hotspots are well known to bird watchers. A case in point is the Eastern Arc Mountains of southern Kenya and eastern Tanzania, a discontinuous chain of wet, forest-clad mountains that rise from the dry savannas. The Eastern Arc is infrequently visited by ecotourists, perhaps because it is not a good place to see the large mammals that make East Africa such an alluring destination. But what the area lacks in furry mega-fauna, it more than makes up for in terms of endemic species, including nearly 100 birds, mammals, reptiles, and amphibians, and at least 800 vascular plants.
The richer, moister soils of the Eastern Arc have long attracted people eager to plant crops or harvest timber. Consequently, the region has lost most of its native forest cover to tea plantations, small farms, and intensive logging operations. Not surprisingly, conservation biologists have expressed deep concern about the long-term survival of many of its endemic species. In June 2011, ecologists John Terborgh, Lisa Davenport, and I had the good fortune to visit two parts of the Eastern Arc, the Eastern and Western Usambara mountains. Our guide (arranged through Dorobo Safaris) was Martin Joho, a young Tanzanian ornithologist with formidable birding skills and unrivaled knowledge of the avifauna of the region. Our brief journey to this hotspot provided an interesting lesson in the challenges of conserving numerous rare species on a shrinking land base.
The focus of our trip was birds, although in fairness to my traveling companions I should note that they took equal delight in the plants, reptiles, and mammals we saw. In the Eastern Usambara Mountains, arguably the richest part of the Eastern Arc in terms of endemic birds, we spent several days at the Amani Nature Reserve, a small government reserve that preserves some precious fragments of the original forest. Here, large flocks of colorful Chestnut-fronted Helmetshrikes roamed through the understory, while groups of Angola pied colobus monkeys jumped around in the canopy. My attention, however, was focused on finding the endemic birds. To my delight, the Banded and Uluguru Violet-backed sunbirds were relatively easy to see along the edges of the forest. The Usambara Hyliota, a dapper but rare Old World warbler, was considerably more elusive, but Martin knew precisely which places to visit, and we were eventually rewarded with a trio of them foraging in the tops of tall trees along the roadside.
Our most difficult challenge, however, was spotting the Long-billed Tailorbird. This strange Old World warbler is one of Africa’s rarest, most range-restricted birds, known from only two locations: the Eastern Usambaras and the Njesi Plateau in Northern Mozambique. Martin, who has studied this species extensively in the Eastern Usambaras, reports that it occurs only within an elevational band of roughly 3,100 to 3,300 feet, an absurdly narrow niche for a bird. Moreover, Bird- Life International classifies it as Critically Endangered, with an estimated global population of fewer than 250 adult birds.
With all that build-up I expected to find the Long-billed Tailorbird in only the oldest, least disturbed forests, but the places Martin took us to look for it were, in fact, tree-fall gaps full of tangles as well as a long-abandoned farm, now overgrown with invasive Lantana bushes. The Long-billed Tailorbird, it turns out, is a disturbance specialist, seeking breaks in the forest where vines and tangles of early successional plants have created a dense understory. Why, then, is it so rare? Why isn’t it everywhere in the poked and prodded, slashed and burned, logged and planted Usambaras? I haven’t a clue. But clearly some aspect of its ecology has kept it highly localized and rare. After considerable effort, I managed to catch a glimpse of a small gray bird with a rusty forehead and a long, thin bill poking its head out of a Lantana thicket, my first and only look at the elusive tailorbird.
With the Long-billed Tailorbird skulking in the weeds and the Green and Uluguru Violet-backed sunbirds bouncing around the sunny edges of the forest, I began to wonder how serious of a threat deforestation could be to the birds of the Eastern Arc Mountains. But I quickly remembered all of the species we hadn’t seen—the shy Spot-throat and the rare Dappled Mountain Robin, for example— as well as the birds that occur in other, even more remote parts of the Eastern Arc, such as the recently discovered Udzungwa Partridge. There are a number of Eastern Arc birds that are closely tied to the intact forests; these tend to be species that forage on the ground. And even the edge-loving sunbirds and Long-billed Tailorbird cannot abide the tea monocultures or maize fields that cover many of the hillsides.
Thus, the Eastern Arc offers both good news and bad news for conservationists. On the positive side, many of the rare birds do not appear to require pristine forests, so it should be possible to protect them in a landscape that includes some logging and agriculture. The bad news is that not all of the rare birds are so tolerant. And even the tolerant ones will likely vanish if too much of the forest is converted to tea plantations or monocultures of maize. There are a number of parks, nature reserves, and forest reserves in the Eastern Arc, but how well these protected areas will fare in the face of a growing human population and increasing demands for natural resources is an unanswered question.
An international team of scientists under the leadership of Cambridge professor Andrew Balmford has spent several years studying the scientific, economic, and social challenges associated with conserving the biodiversity of the Eastern Arc. One of their primary goals has been to put a dollar value on the full range of goods and services associated with the hotspot’s forests—not just from timber but also from carbon storage, water provisioning, ecotourism, biodiversity, and other ecosystem services. I hope that the collective value of these benefits, when fully accounted for, will exceed what could be gained by continuing to clear the forests for agriculture and other uses, thereby providing the Tanzanians and Kenyans with a strong economic incentive to protect the remaining forests. But if that proves not to be the case, then it’s up to all of us in the international community to provide them with the resources they will need to keep this particular ark afloat.