The Common Eider by Chris Waltho and John Coulson<b>The Common Eider</b>by Chris Waltho and John Coulson. 2015. T &amp; AD Poyser, London, UK. 352 pages, 8 color plates, 146 text figures. $85 (hardcover). ISBN 978-1-4081-2532-8.

The authors of The Common Eider take on the daunting task of summarizing the biology and ecology of this well-studied species. What makes this task especially challenging is the species itself. With six described subspecies, a huge breeding range across the Northern Hemisphere, and vastly different relationships with humans across that range, it is difficult to generalize about Common Eiders (Somateria mollissima). The authors, wisely in my opinion, do not purport to summarize all that is known about this popular bird, but instead focus on certain key areas, especially topics on which they themselves have collected extensive data from the United Kingdom. The book contains 14 chapters and 7 appendices. In general, the chapters are those typically found in a book describing the natural history of a species, while the appendices offer various details, including lists of important sites for this species and their predators and prey. There are 8 pages of color plates, and the photographs, especially by John Anderson, are fantastic. I would have enjoyed more photographs, especially a series of high-quality photos of each subspecies. Chapter 1 provides an extensive description of the species and ends with some physiological considerations. Chapter 2 talks about one of the more interesting aspects: phylogenetic origins and the variation seen among and within the six extant subspecies. Chapter 3 comments on current distribution and movements throughout the species' northern range. Chapter 4 looks at the diet and feeding behavior of Common Eiders and includes an extensive synthesis of the importance of various prey items and benthic habitats. Chapter 5 provides a relatively high-level summary of the predators, parasites, and diseases of the bird. The next 7 chapters (6–12, what I would consider the core of this volume) focus on various aspects of breeding ecology and life history. In these chapters, the authors present new data from the UK and use these data along with published material to present their views on various aspects of the species' breeding ecology. Chapter 6 examines the phenology of the species' breeding and whether there are changes over time and across its range. Chapter 7 delves into what is turning into a complex story: how Common Eiders end up incubating eggs within their clutches that do not belong to them. Sources of variation in clutch size are considered in Chapter 8, which includes much new data from the authors and other sources. Incubation and hatching are addressed in a short Chapter 9. The authors change pace in Chapter 10 and give us more of an essay on the topic of whether Common Eiders are truly colonial. Ducklings are the subject of Chapter 11, with a focus on another peculiar aspect of the biology of Common Eiders: the crèching system. Mortality is the focus of Chapter 12, and here, as elsewhere in the book, quite a bit of new data is presented. The past and current relationship between Common Eiders and humans is explored in Chapter 13. The final chapter is authored by Diana Solovyeva, who is fortunate enough to have worked with all four species of eiders: Common Eider, King Eider (S. spectabilis), Spectacled Eider (S. fischeri), and Steller's Eider (Polysticta stelleri). This chapter compares various aspects of the biology of these 4 species. The book takes a critical look at many aspects of Common Eider biology, and the authors challenge a number of previous contentions, often supported by their own extensive data. I have no particular issue with these critical evaluations, and the process of critical evaluation has a central place in any scientific endeavor. But I found that it gives the book a bit of a negative tone. I've been lucky enough to work with a number of Common Eider populations and subspecies, and one thing I have experienced is that each one is surprisingly different. Different nesting habitats, different harvest pressures, different migration strategies, different predation pressures, and different food bases all seem to lead to different behaviors and life histories. For a duck, the Common Eider is a uniquely diverse species, and that makes me wonder whether some of the differences found among studies just reflect how diverse Common Eiders can be. But I must admit I particularly enjoyed Chapters 7 and 10, in which the authors really get into the puzzling issues of the source of eggs in clutches from other females and whether this colonial species is actually colonial at all. These chapters challenged some of my own presumptions about these birds, and I found the arguments presented by the authors quite compelling. Whether these ideas are supported by data collected down the road remains to be seen, but what is clear is that we still have much to learn about Common Eiders. Determining the audience for this book was not easy for me. Many of the chapters have descriptions of basic life history or ecological theory, and there the material would appear to be pitched toward an interested lay audience and naturalists. In other sections the authors dive deeply into specific primary papers and critically evaluate the authors' findings—material that would seem to be more relevant to the professional community. In the end I think this book has a place on the shelves of both groups. There is plenty of both general and specific information on the Common Eider for interested naturalists. For professionals, a lot of new data is presented in the book, much of it based on long time series. The analyses of these data are simple, and details on the methods of data collection are sparse, so caution will be needed when integrating this information into the published literature. But the important point is that these impressive datasets and summaries are now available to further our understanding of this important species.

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