Despite its extensive Holarctic distribution, the Merlin (Falco columbarius) remains a rarely studied species (149 papers listed in Web of Science from 1975 through 2015) when compared to the Peregrine Falcon (F. peregrinus; 574 papers) or American Kestrel (F. sparverius; 536), though not in comparison to the Gyrfalcon (F. rusticolus; 104). Given the limited research on Merlins in mainstream journals, Sale has done a remarkable job of delving into the relative wealth of knowledge found in regional or local journals, along with data and insights from a recent synthesis by Morozov et al. (2013). The target audience for this compilation appears primarily to be knowledgeable raptor or falcon/falconry enthusiasts. The book's lighter tone is set in early chapters that make reference to Merlins in the context of falconry and the anecdotal observations that are scattered throughout, though the middle chapters seem more appropriate to a scientific audience. There are 12 chapters, beginning with a two-chapter overview of falcons that leads into chapters explicitly discussing various topics related to Merlins, including foraging behavior, diet, breeding, survival, movements, wintering, and population status and trends.
Chapter 1 is a review of the currently disjointed state of falcon systematics. It would have been more effective to focus strictly on Merlin taxonomy and provide a more detailed overview of the genetic work suggesting that the Merlin may actually be two distinct species (Nearctic vs. Palearctic) that diverged up to a million years ago. Instead, Sale briefly presents the latter idea but dismisses it in favor of the more conventional single-species-with-multiple-subspecies model, as his lead-in to a description of the 9 widely recognized subspecies.
Chapter 2 includes an assortment of general characteristics of falcons. A more effective organization for the book might have been to present the information from this chapter as context within the remaining chapters. Chapter 3 presents subspecies descriptions and distributions but lacks a synthesis of morphological measurements to facilitate comparison and support qualitative statements about differences in size among subspecies. Data on pages 50–51 (taken from Birds of North America; Warkentin et al. 2005) are presented as combined values for all North American subspecies; these include errors and, in fact, reflect values for the Prairie Merlin only. Later in this chapter, the description of F. c. aesalon is the first of many instances where data from Morozov et al.'s (2013) compilation are briefly described, with the suggestion that readers should consult it for additional information. Sale could have provided a great service to those interested in Merlins of that region but unable to read Russian by giving more detail from this work. Likewise, the chapter on diet (Chapter 4) was an opportunity for Sale to synthesize data on prey selectivity and identify foraging patterns based on the morphology, size, and ecological habits of commonly selected prey items across Merlin populations. Instead, the chapter is simply a reporting of prey species from numerous studies. Sale does mention that Merlins frequently focus hunting efforts on the most common, appropriately sized prey available, and this could have been an interesting starting point for the chapter rather than serving as a side note.
Chapter 6 is one of the best syntheses of information in the book, bringing together the outcomes of Canadian and Dutch studies on small-raptor energetics. Likewise, the sections on territory and pair formation in Chapter 7 are well done. There is a strong summary of how the spatial division of habitat fits in with resource availability, though it would have benefited from a brief discussion of how territory and home range were defined in the highlighted studies. Chapter 9 provides a thorough description of the wintering ranges for each subspecies (although note that some results reported for Taiga Merlins were largely derived from Prairie Merlins). Perhaps this material could have been merged with the information on breeding ranges presented in Chapter 3, so that maps could have detailed both breeding and wintering ranges.
The discussion about causes of mortality and the significance of chemical contaminants in Chapter 10 is effective, but the story becomes fragmented where the impact of DDT and its relatives is discussed in Chapter 12. Sale makes some interesting observations about recent controversy regarding the use of neonicotinoids and whether such problems are similar to those caused by contaminants in the past. Chapter 11 is a good amalgamation of work from Scandinavia and Canada on interactions with other species (“friends”) that benefit Merlins, but the section about species that prey on Merlins (“foes”) returns to simply reporting results from a series of studies.
The author's passion is displayed in Chapter 12 through his description of populations facing ever-changing threats. This is particularly true in the discussion of the Merlins of the British Isles. Here, he explains the basis for assessing the impact of contaminants through use of the eggshell thickness index. He then examines the mystifying decline of British Merlins due to an apparent combination of residual pesticide contamination, influences of mercury on productivity, human alteration of critical habitat, and the decline of important prey populations (especially in winter).
Editorial errors made the book less reader-friendly than it could have been. Typos occur throughout, and their high frequency in some sections was especially distracting. Table-caption and footnote fonts are not distinct from the normal text (unlike those for figure captions) and often blend together when viewed across multiple pages. References to material in other chapters are based on the chapter number and/or name, but chapter numbers are provided only in the Table of Contents. Some figures lack critical information (e.g., Fig. 23 doesn't indicate which color represents which sex), or redrawing has omitted legend information (e.g., color coding for bars in Fig. 1b is missing and the colors used don't match the legend for Fig. 1a), necessitating reference to the original source. In Table 6, the citation of “Newton et al. 1978” should have been corrected to “Newton et al. 1984.” Additionally, page 259 presents a picture of a female American Kestrel rather than a female Taiga Merlin as indicated by the caption.
My familiarity with Merlins originates from work in the Canadian prairies. What was reinforced as I read this book was the substantial variation in how individuals of the different subspecies go about their lives. Sale's detailed compiling of information makes this a valuable resource for those interested in the 9 subspecies of Merlins; it also clearly reflects current knowledge gaps. These elements make the book a valuable contribution. But detracting from that value are the primary focus on reporting rather than synthesizing knowledge, the distracting typos, and the occasional outright errors in presentation of redrawn tables and figures or in interpretation of findings. For raptor enthusiasts, this book gives a good overview of what we know about Merlins. The problems with presentation are such, though, that I would caution researchers unfamiliar with the Merlin literature to carefully check the original sources before citing the book's interpretations.
