Silence of the Songbirds provides an eloquent and readable overview of the threats facing migratory songbirds and other terrestrial birds in the Western Hemisphere. Bridget Stutchbury introduces the main topics in the book with vivid descriptions of birds and their habitats. Personal accounts of fieldwork—leading students on their first day in a tropical rainforest, an early morning walk into a Pennsylvania forest, canoeing in a marsh as thousands of martins descend into the reeds, and watching migrants in a Costa Rican garden—engage the reader and set the stage for discussions of bird ecology. Throughout the book, Stutchbury uses effective images to convey the magnificence of bird migration. A migratory wave of birds is "a living storm" that "will pass by unnoticed by almost everyone in its path, even though it will rage for over six hours and cover several hundred miles" (p. 18).
This book is not intended to be a thorough scientific review of the literature. There are no citations in the text (only a list of sources for each chapter at the end of the book), and topics are explained with representative examples, not a thorough discussion of different studies and conflicting results. In the Acknowledgments, the author explains that she "deliberately glossed over some of the controversies" about the decline of migratory birds and used terms that will be accessible to general readers, even when a more technical term would be more precise. Partly as a result, her accounts should interest and inform general readers, who are clearly the target audience for this book.
One major weakness of the book is in the treatment of population declines in migratory birds. As the author indicates, it is appropriate to gloss over the technical debates to present a general overview. It is not appropriate, however, to simplify research results so much that the conclusions are misleading. An uninformed reader of this book will come away with the impression that the steady, linear and steep declines in the populations of Eastern Kingbird (Tyrannus tyrannus), Kentucky Warbler (Oporornis formosus), Wood Thrush (Hylocichla mustelina), and Bobolink (Dolichonyx oryzivorus) illustrated in Figure 2.4 are typical of Neotropical migrants. After all, they were chosen because they "live in different habitats, eat different foods, and spend the winters in different tropical countries" (p. 29). At no point in the accompanying text, which describes dramatic declines in migratory birds revealed by the Breeding Bird Survey (BBS), do we learn that analyses of BBS results from eastern North America indicate that 41% of Neotropical migrant species had positive population trends since 1966 and that 24% showed significant increases (Sauer et al. 2007). The proportion of woodland breeding species in eastern North America with significantly increasing trends (37%) is even greater and is higher than the percentage of species with significantly declining trends (28%). The BBS results indicate that most species of forest-dwelling, Neotropical migrants in eastern North America (which are the focus of much of this book) have had stable or increasing populations since 1966. Increasing species include the Red-eyed Vireo (Vireo olivaceus), Blue-headed Vireo (Vireo solitarius), Hooded Warbler (Wilsonia citrina) and Ovenbird (Seiurus aurocapillus), all of which are mentioned repeatedly in the book. Similarly, Stutchbury describes evidence that migrants are declining based on banding results at Manomet Center for Conservation Sciences in Massachusetts, but she doesn't mention a rigorous analysis of banding results and observational records at Long Point, Ontario that indicated that more species of Neotropical migrants increased than declined between 1961 and 1997 (Francis and Hussell, 1998). The Long Point results also revealed that many species showed roller coaster fluctuations in abundance, with periods of dropping populations followed by periods of increase.
Even migratory species with increasing populations will be in trouble in the future if destruction and fragmentation of breeding and wintering habitat are not halted and if the other threats to birds described in this book continue unabated, but an objective analysis of recent population trends is more than a technical concern. Conservationists who go to public hearings armed with oversimplified assessments of population declines in migratory birds will be discredited by opponents who have easy access to BBS data on population trends. More important, this approach does not help us distinguish species that are in immediate trouble from those that are not. For example, the list of declining species of forest migrants in eastern North America is dominated by species associated with open or early successional forest habitat (regenerating forest, open woodland or forest openings), which immediately suggests that maturation of forests and the suppression of natural disturbances in this region may be driving some of these declines. This perspective is lost with an approach that assumes all migrants are in imminent danger. Also, nearly all grassland birds in North America have declined steadily and severely, so these species should have a particularly high priority for research and conservation. Among the species associated with mature forest, we should particularly focus on the minority of species (including the Wood Thrush and Cerulean Warbler, Dendroica cerulea) that have declined substantially and steadily. Why do these species show a different pattern from other mature-forest migrants, and what can we do to restore their populations?
In contrast to the discussions of population trends, the explanations of threats to bird populations are more thorough and balanced. For example, Stutchbury describes the high mortality rates for raptors at an early wind turbine farm at Altamount Pass in California but explains that facilities with more advanced wind-turbine designs have relatively low rates of bird mortality. She also presents a thorough overview of the effects of forest fragmentation on birds, contrasting the different patterns in eastern deciduous, western montane and boreal forests. Her discussions of the effects of habitat change on bird populations are both clear and thorough. The only exception is a somewhat confusing discussion of edge effects (Chapter 9), which seems to confound two hypotheses: that nest success is often lower close to edges and that forest birds tend to avoid using edges for nesting. The first hypothesis has been supported by numerous studies in a wide range of habitats where natural habitat abuts anthropogenic habitat, while the latter hypothesis turns out not to be valid for many species that were once considered forest-interior specialists. If anything, the absence of edge avoidance may increase the negative impact of edge effects (rather than prove that they don't exist). The same chapter includes an insightful discussion of the importance of extra-pair mating and social "neighborhoods" of birds of the same species. The absence of territorial neighbors in small patches of forest may make these sites less attractive as breeding habitat, which would help explain the negative effects of habitat fragmentation on some species of forest birds.
One of the most effective features of the book is the convincing and detailed assessment of the "ecological services" provided by songbirds. Far from merely being decorations in the natural habitat, songbirds play key roles in reducing populations of leaf-eating insects and dispersing seeds of shrubs and trees. This is a critically important point to make for general readers who may have minimal investment in saving birds as objects of fascination and beauty. Stutchbury also does an excellent job of emphasizing how we can help conserve bird populations both through personal decisions and by influencing public policy. The chapter on the history of coffee and the environmental impacts of different types of coffee production (Chapter 5) is one of the highlights of the book. People who read this book are likely to be more careful about what type of coffee, vegetables and wood they buy, and more discerning about how they look at the lights on cell phone towers or in tall buildings, and how they assess the use of nonpersistent pesticides. They will certainly be more attuned to the importance of preserving large expanses of habitat in the tropics as well as in the northern breeding areas to support Neotropical migrants, and the key role of small islands of natural habitat for sustaining birds as they pass through a region on migration.
In summary, I recommend this book to committed naturalists, students and general readers who want to learn about songbird conservation, and for land managers and researchers who will benefit from the book's thoughtful and concise overview of the multiple threats to North American songbird populations.—ROBERT A. ASKINS, Department of Biology, Connecticut College, New London, CT 06320. E-mail: raask@conncoll.edu
