In 2013, Loss et al. reviewed the scientific literature and generated estimates of the numbers of birds, mammals, and herpetofauna killed by domestic cats annually. The paper caught the attention of a variety of media outlets and sparked a polarizing and sometimes rancorous public debate about the impacts of free-roaming cats on wildlife. In Cat Wars, Peter P. Marra, a coauthor of the Nature Communications paper, teams up with writer Chris Santella to explore the issue in more detail. Cat Wars is an aptly evocative title, referring to both the heated controversy over the impacts of free-ranging domestic cats and the wildlife casualties that are at the heart of the debate. Without reading the book, detractors might conclude that the authors are proposing a war on cats, which is unfortunate because those critics are precisely the audience that would most benefit from this highly readable missive.

Although the book primarily emphasizes how free-roaming cats affect wildlife—either directly, via predation, or indirectly, by inducing behavioral changes or transmitting diseases (e.g., Cresswell 2008, Bonnington et al. 2013, Loss and Marra 2017)—a wide range of subjects and relevant history is discussed. One sobering chapter focuses on the burgeoning public health crisis posed by Toxoplasma gondii, a parasite linked to a range of human ills—including miscarriages, birth defects, and schizophrenia—for which felines, including domestic cats, are the definitive hosts. Because it persists in the environment and can wash downstream into ocean ecosystems, T. gondii has also been implicated in the deaths of a number of imperiled marine mammal species, a fact that may come as a surprise to many readers. While less common in the United States, the authors also discuss the role that cats play in the transmission of other zoonotic diseases such as plague and rabies. The book is interspersed with engaging narratives and profiles of both bird and cat lovers, and even delves into such topics as the rise of birding in North America and the prominent role of cats in Internet culture.

Most chapters are written clearly enough for a nonscientific readership, but important subjects occasionally are not sufficiently explained for a reader who has never been exposed to certain ecological concepts. For example, in Chapter 2 the authors describe the domestic cat's status as one of the world's worst invasive species, outcompeting or edging native species from their established niches (e.g., Lowe et al. 2000), but they neither define an ecological niche nor expand upon the concept of niche overlap, which might have been useful to someone unfamiliar with these terms. Overall, however, the authors nicely summarize and distill the scientific literature, such as when they cogently explain the quantitative modeling process Coleman and Temple (1996) used to estimate the numbers of birds killed by cats in Wisconsin—work that consequently led to a storm of controversy that has continued decades after publication. Likewise, they carefully dissect the methodologies Loss et al. (2013) used to estimate the impact of free-ranging domestic cats on wildlife populations, which have incited similar debate in recent years.

Several chapters are devoted to addressing the trap-neuter-return (TNR) method, which is endorsed by many cat advocacy and animal welfare groups as the best technique for reducing feral cat populations. The practice, which involves trapping and sterilizing cats and releasing them outdoors at the original capture site, has a number of serious flaws that are frequently denied or overlooked by cat groups and policymakers (Longcore et al. 2009). The book discusses current research on the efficacy of TNR and refutes common claims made by cat advocates. While doing so, it is clear that the authors strive to avoid coming across as too adversarial; they attempt to consider the perspectives of well-meaning proponents of TNR. Several chapters feature anecdotes and sympathetic profiles of cat-colony caretakers and animal advocates involved with TNR; these profiles reveal individuals who are overwhelmingly motivated by compassion and the desire to help stray and feral cats. The authors believe that their actions are misguided but that their hearts are in the right place, while justifiably questioning why this compassion does not extend to other animal species.

While all parties may agree that the world hosts too many unwanted cats, there are still those who refuse to acknowledge that those cats affect wildlife. As evidence of this, the authors discuss a study by McDonald et al. (2015), which depressingly revealed that even owners whose cats killed and brought home prey did not accept that cats might have substantial impacts on wildlife populations. The challenge, then, is to determine what angle will convince people to be invested in solving the cat problem when they have little interest in ecological conservation. This book's frank discussion of the public health risks from free-roaming cats, as well as the dangers to cats themselves (e.g., they are more likely to be hit by cars, to be killed by coyotes, to contract diseases, etc., than their indoor counterparts) may prove more convincing to certain readers than will concerns about songbird declines.

After outlining the scope and magnitude of the free-roaming cat problem, the book's penultimate chapter proposes a variety of solutions, some more plausible than others. It may be unlikely for cat food companies to start labeling their packages with American Bird Conservancy “Cats Indoors” messages of their own volition, but encouraging more veterinarians and shelters to espouse the benefits of keeping cats indoors is surely achievable. While the authors state that it is impossible to endorse TNR given its many failings, they acknowledge that it will continue with or without the input of conservationists, and hence offer suggestions for improvement, such as striving for much higher rates of sterilization in order to substantially reduce feral cat numbers (Foley et al. 2005).

Cat Wars exhorts the scientific and conservation communities to take a more active role in local politics and lobbying, arguing that the claims of cat advocacy groups, when unfounded, must be challenged with facts. Scientists are obligated to communicate their findings to a broader audience, as well as to provide scientifically supported advice and recommendations to policymakers and legislators concerning outdoor cats. The sometimes vitriolic response to such information presented by Loss et al. (2013) and the Coleman and Temple papers (1989, 1993, 1996), coupled with an increasing public distrust of scientific authorities among certain segments of the population (Gauchat 2012), might make this an unappealing endeavor for many researchers, but it is a necessary one.

The authors also point to several hopeful instances of collaborations between animal welfare and conservation organizations, making the case that extending an olive branch to your opponents may be more effective than beating them with it. One particularly interesting example involves an unlikely alliance between the Audubon Society of Portland and the Feral Cat Coalition, in which the two groups have teamed up to reduce the number of free-roaming cats on a local island. While such cooperative efforts may not yet be widespread, it is a model that seems to show real promise.

Just as piling on the evidence won't change the minds of die-hard climate change deniers, Cat Wars is unlikely to convince the most ardent feral cat advocates to switch perspectives. However, those open and willing to learn more about the subject will find much to ponder in the pages of this book, and there are enough compelling narratives and historical details to engage even casual readers with no prior interest in the topic. The book balances a thorough overview of research on free-roaming cats with a nuanced exploration of the moral complexity of the problem; as such, it will prove a worthwhile read for both scholarly and lay audiences (as well as for that one neighbor whose cat keeps wandering into your yard).