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1 July 2011 Living on the Edge: Wetlands and Birds in a Changing Sahel
James A. Kushlan
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Most North American ornithologists know that the Sahel is that semitropical zone between the Sahara and tropical Africa, and that R. E. Moreau's classic early-70s book on bird migration in Africa identified this then little-known area as of importance to wintering Palearctic migrants. They may also recall it as the site of massive human suffering in the drought of a couple of decades ago. Beyond that, unless one is studying the birds that use the zone or has wanted to visit Timbuktu, most North Americans don't know much more and haven't much compulsion to learn. Palearctic ornithologists know and care more, but their source materials have been limited. For those not working on Palearctic migrants, why should precious time be spent on a book that is essentially regional in focus and outlook? The reasons are several: it is a wonderful book, well written, well illustrated, well presented, and that is a rare joy; it is an even rarer example of excellence in primary scholarship at the book scale of publishing; it is a model of wise use (and in some cases deliberate nonuse) of existing data; it tells an important tale of the complexity of unraveling environmental change; and it is a case-history harbinger of what likely is to come to other parts of the globe, because it is in the Sahel that the effects of climate change are not modeled predictions but real and compelling facts on the ground.

This book aims to reveal the ecology of the Sahel and the Palearctic birds that use it, particularly waterbirds. Why waterbirds in the seasonally desiccated landscape of the sub-Sahara? Because it is also a landscape containing dry-country rivers, wetlands, and lakes, including the Niger River and Inner Niger Delta, the Senegal River and Senegal Delta, Habejia-Nguru floodplain, Lake Chad and its basin, and the Sudd, habitats used by a half billion European birds (more or less). The Sahel first came to my attention years ago when it was unexpectedly discovered that survivorship of southern European Purple Herons was correlated not with what was happening in Europe but with rainfall in the Sahel, inversely so. It turns out that about a quarter of European birds migrate seasonally to the Sahel during the northern subtropical drying season, and these species are, for the most part (75 of 127), in a state of population decline. Conditions in the Sahel are a prime candidate by way of explanation. The climate in the Sahel has been changing complexly for thousands of years, and over the last decades mostly getting drier, although somewhat wetter more recently. The authors show that of all the proposed explanations, this drying is most closely correlated with ocean warming—global climate change in action. They explore why most climate-change models do not detect the Great African Drought of 1972–1992 and find that the most acceptable of current models show a continuation of current conditions with further drying in subsequent decades, thus setting the stage for critical bird-conservation issues of the future. For today, the current problems are people-caused.

The first chapters are analyses of the abiotic and biological characteristics of the Sahel, including climate, vegetation, rivers, and land use. These are clearly written, full of original analyses, superior interpretation of the literature, excellent illustrations, and mind-bending use of original modeling and satellite data—a tour de force of geography. They show, for example, that, contrary to the previously accepted paradigm, which once underpinned the Desertification Convention, desertification is more the result of climate change than of human activity, which can, however, prolong drought recovery. Massive human population increases and urbanization, increases in farmed land and the elimination of land rotation, dams and water use, destruction of native forests for charcoal, planting of insect-free trees, hunting, and elimination of the once huge herds of grazing wildlife—much of this in the past 50 years—all contribute to a continuation of the pattern of habitat loss for birds, which began in drought.

The second part of the book devotes chapters to the great wetlands and to rice farming. The Inner Niger and Senegal deltas are treated in most detail because they are the better known. Dams, irrigation, land-use changes, climate change, and population pressures have changed the way these Sahel wetlands function. The seasonal flood pulse and seasonal dry-down have been altered to the extent that 15–20% of the floodplains of the Inner Niger Delta have been lost and the Senegal Delta was converted from a wetland of seasonally fluctuating salinity to freshwater. The Goliath Heron, five species of storks, and the Hammerkop, all abundant in the 1930s, no longer are found or breed in the Inner Niger Delta, because of both habitat change and human consumption. On the other hand, over 100,000 pairs of colonial waterbirds (in large part Cattle Egrets) are estimated to still nest in the Inner Niger Delta, and wintering waterbirds still number in the millions. In the Senegal Delta and Hadeija-Nguru floodplains, dams have totally changed the hydrology and led to invasions by exotic plants. Active management using artificial flooding to simulate a more natural hydrology has maintained the conservation values of Djoudj and Diawling national parks, which, although mere patches of remnant habitat, support hundreds of thousands of waterbirds. The world-famous story of the “drying of Lake Chad” is well covered and shown to be much overblown in the public mind, the danger coming not so much from the long-term trend of drying as from governmental determination not to learn the clear lessons from elsewhere but to continue to plot and scheme to stabilize lake levels. The Sudd, the largest wetland of the world, is also one of the least known; little more is known now than in Moreau's time. Unfortunately, according to the authors' analyses, the most complete survey of waterbird numbers for the area seems to be wrong. In fact, throughout the book, the authors work very hard to get the best possible population estimates by evaluating a hodgepodge of census and survey data of varying methodology, quality, and extent that they have procured from various sources for the individual species, the major wetlands, and the Sahel as a whole. They call bad data bad data, estimates estimates, and complain clearly about the pitfalls in existing monitoring data, much of which is very poor and lacking in any sense of error estimation. They present their numerical guesses as best they can; I have little doubt anyone has done it better. They similarly do what they can with migration and winter mortality data.

In the third part of the book, 31 chapters are devoted to the birds. The first, 40 pages long, details how the Sahel serves as the wintering area for the northern continent; the second explains the role of locusts; and the last three discuss the Sahel in relation to Europe. In between, chapters of a few pages each cover individual species of European migrants, mostly waterbirds, including status, trend, migration, and distribution, nearly all with maps of banding recoveries. The book ends with an analysis of the connectivity of the Sahel with European bird trends, an exceptional attempt to discern trends and causality from messy data. Almost 1,450 references, an excellent index, and technical chapter endnotes support the materials covered.

This is a book that has interesting things to say on most pages and real treasures on some. Although the book is multi-authored, its voice is amazingly consistent throughout. The figures and color photographs are superior, the latter not only illustrating the point being discussed but also revealing the harsh beauty, mystery, and human face of the region. The authors set out on this project in the early 2000s, when they realized how little information was available. They decided to get control not only of the literature but also of unanalyzed databases and to do original analyses, modeling, and field research as required to more fully understand and tell the story. This original research makes the book special. The overall impression one takes from each of the chapters is that the authors speak authoritatively. They have no hesitancy in taking on long-held views and prior misanalyses or in drawing conclusions from the literature and their own analyses that ring both true and fair. It is a book to be recommended to ornithologists and bird conservationists alike, worldwide, and a necessity for any university library.

© The American Ornithologists' Union, 2011. Printed in USA.
James A. Kushlan "Living on the Edge: Wetlands and Birds in a Changing Sahel," The Auk 128(3), 594-595, (1 July 2011). https://doi.org/10.1525/auk.2011.128.3.594
Published: 1 July 2011
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