This hefty and beautifully produced volume truly is a superb book. It mainly focuses on the ecology of Palearctic birds in the Sahel and offers a fascinating synthesis of numerous studies and the authors' own field work, conducted between 1982 and early 2009. Their field work began as low-budget affairs, partly financed by the participants themselves, but have since developed into larger-scale projects encompassing several West African countries. The authors' statement that 'Paid, underpaid or unpaid, the passion remained the same' shines through on every page.
Each year, hundreds of millions of birds breeding in Europe undertake the daunting journey south to sub-Saharan Africa, where they spend the greater part of their lives, mainly in the c.500 km-wide band of northern savannahs stretching 5,500 km from west to east. Although this habitat can appear superficially poor and dry, especially during the Palearctic migrants' stay, it is actually a complex ecosystem, where seasonal variations in the leafing, flowering and fruiting of trees and shrubs provide food and shelter for birds throughout the northern winter, i.e. the region's dry season. Survival here depends mainly on unpredictable rainfall in the short wet season and the flood extent of the inundated areas. Droughts, whose frequency and duration have increased since 1969, have a huge adverse impact on birds, which has been magnified by negative habitat changes associated with human population growth, such as deforestation, reclamation of wetlands and irrigation. Additionally, overgrazing and hunting take their toll. It should therefore not come as a surprise that population numbers of 75 out of 127 trans-Saharan migrants are decreasing, with those wintering in the Sahel suffering the strongest declines.
The book, which pays tribute to the ideas aired by Reg Moreau - the 'forefather of African ecology' - in The Palaearctic - African Bird Migration Systems (1972), documents and analyses the multiple problems faced by trans-Saharan migrants. It does so extremely thoroughly and in a highly readable and attractive form, despite the huge amount of information presented and the often sad message. The whole is lavishly illustrated in full colour throughout, with hundreds of clear diagrams and maps, 35 tables and nearly 500 excellent and functional photographs - even the index has delightful bird drawings, by Jos Zwarts, at the bottom of every page! The language occasionally betrays that the book was written by Dutch researchers, but the overall quality of the work is of such a high standard that to mention it is almost nitpicking.
First, rainfall, rivers, vegetation and land use in the Sahel are presented, followed by chapters on the major wetlands: the Inner Niger Delta, the Senegal Delta, the Hadejia-Nguru floodplains, the Lake Chad Basin, the Sudd and the rice fields. Next are 27 chapters devoted to single bird species, selected to identify events pivotal to numerical fluctuations, such as migration strategies, distribution and habitat selection in Africa, and changing conditions on the breeding grounds. These species range from Grey Ardea cinerea and Purple Herons A. purpurea through Black-tailed Godwit Limosa limosa and Eurasian Wryneck Jynx torquilla to Lesser Sylvia curruca and Common Whitethroats S. communis. A chapter, by Wim Mullié, gives an overview of recent outbreaks of locusts and grasshoppers and the use of chemical pesticides for their control, explains the ecology of these insects in the region, and discusses bird–acridid relationships and the 'ecological service' provided by birds by suppressing acridid populations. The book concludes with a discussion of the impact of ecological changes in the Sahel on Eurasian bird population trends. Evidence accumulated over many years of field work, like that by the authors, indicates that population fluctuations of several species are indeed largely determined by rainfall and flood extent in the Sahel. This, coupled with changes in the breeding areas and stopover sites along migration routes, leaves little scope for optimism. Nevertheless, Leo Zwarts and his co-workers hope, 'against their own better judgement', that their negative predictions will prove incorrect and that Afro-Palearctic birds will be sufficiently resilient to cope with the changes.
New data constantly lead to new lines of research, whilst a lot of questions remain unresolved. Fortunately, for what is known on Palearctic birds in the Sahel we now have an excellent synthesis which constitutes a milestone for ecological studies in the region. This outstanding book is a splendid achievement for which the authors and publisher are to be congratulated.