O'Connor, Terry. 2013. Animals as Neighbors: The Past and Present of Commensal Species. East Lansing: Michigan State University Press.

(Summarized by Mark Suchyta, Animal Studies Graduate Program, Michigan State University Press)

In Animals as Neighbors: The Past and Present of Commensal Species, Terry O’Connor explores our relationships with the animals that we take for granted—those who live among us and rely upon our environments for food and shelter. O’Connor begins the book with a personal anecdote. He recalls when he was a young child and was fascinated by watching the gulls near the seashore. In doing so, he demonstrates how children are fascinated by animals and how, as adults, we continue to be intrigued by and rationalize uour relationships with non-humans. He contends that this interest in itself is a reason to study non-humans, but there are many other reasons. Animals intersect with our lives in a variety of ways, as symbols and icons, laborers, rehabilitators, sources of food, companions, and so forth. He writes, “Animals are central to our individual and collective lives” (1).  
O’Connor reminds us that we, too, have had tremendous impacts on animals’ lives. Some scientists claim we live in an era known as the Antropocene, where human activities are impacting every corner of the earth and its ecosystems. This is not something that happened suddenly (although it has been exacerbated in the last 150 years). For their entire existence, humans have altered the environment to their liking. This has impacted the animals around us; some have suffered because of it, others have adapted or even thrived. Some have even found themselves living close to and among humans, relying on them for food and shelter. It is this latter group of animals that O’Connor explores in this book—those who voluntarily live among humans in our constructed and modified environments. Specifically, he is interested in mammals, birds, and other larger animals. While he acknowledges the bounty of microorganisms and insects that benefit from the human environment, O’Connor chooses to focus on these larger animals as they are easier to identify not just in the present, but through archaeological evidence, which he relies upon heavily throughout the book (O’Connor is an archeologist by training).
               O’Connor defines these species as commensal. He adopts this term from ecology, where it refers to a relationship where one animal benefits and the impact on the other is generally neutral. He contrasts this with other relationships between species, such as parasitism, where one species is negatively affected. O’Connor describes our relationships with commensal species as “ambiguous”. Domestic animals are not commensal as they are entirely reliant on humans and are actively adopted into our communities. They are not feral, as feral animals exist because they were once domestic. Yet, they are not truly wild either, as they actively participate in the human environment. To be commensal, a species must meet two criteria. They must benefit from the human environment, built or modified, for both food and shelter. Through exploring current and historical commensal species, O’Connor seeks to reverse one of zooarcheaology’s main research questions by asking, “What did those people mean to these animals?” (5).
               While traits vary among commensal species, O’Connor lists four characteristics that are particularly advantageous for adaptation and success. First, being an omnivore is beneficial, as this allows animals to take advantage of the diverse refuse and sources of energy that are concentrated near human settlements. Second is not being antagonistic or territorial. This allows animals to better exploit concentrated feeding opportunities. Third is flexibility in breeding season and relatedly, forth is a high rate of reproduction.

In the first chapter, O’Connor discusses what constitutes the human environment. He defines two different zones: the built environment, such as cities, and the modified environment, places that are not necessarily urban but have been altered by human activities. He describes six characteristics of the human environment. First is disturbance; humans actively build and modify. This can threaten some species and their niches while opening up opportunities for others to enter into commensal relationships with us. Second is redirection and concentration of ground water. This, too, alters habitats and niches. Third is the active replacement of “undesirable” biota by more “desirable” biota. Forth is humans deposit refuse, making our environments large energy sinks and potential sources of food for other species. Fifth is human settlements are connected by roadways, canals, rails, and footpaths, creating networks of disturbance which may discourage some species while attracting others. Sixth, people tend to construct a built environment, which creates places for animals to live such as cliffs, rooftops, and so forth. He provides an example of the urban bird, which takes advantage of the numerous plateaus and vertical cliffs free of human disturbance, separated by canyons with rich feeding opportunities.
               In chapter 2, O’Connor discusses how we can draw evidence, both present and historical, of commensalism. He discusses the challenges of relying on historical evidence as many details are omitted based upon whatever the humans at the time found interesting. Small samples are also problematic. For contemporary examples, we need to use caution when relying on anecdotes from the Internet and so forth. On one hand, they might be strange isolated cases. On the other, accounts may represent the experiences of millions of people. O’Connor, an archeologist, by training, discusses some of the challenges specific to his field and how evidence is lost over time, a topic he continues to discuss in chapter 3, “The Archaeology of Commensalism”.
               In this third chapter, O’Connor attempts to explore how far back into history does evidence of commensalism exist and furthermore, how has commensalism possibly impacted our own evolution as a species. He discusses the earliest shreds of evidence, remains of animals in and nearby caves where humans resided. While it can be challenging to ascertain how our early ancestors interacted with these animals, O’Connor presents evidence that reliance on humans for food and shelter is not a recent phenomenon. He describes foxes, crows, and wolves which began to reside near human settlements to take advantage of refuse. This effect was further exacerbated by the development of agriculture, which greatly altered landscapes and provided new and reliable sources of food. The rise of agriculture also resulted in the development of a more sedentary lifestyle, yielding villages and towns. This created further concentrated sources of refuse as well as new potential habitats.
               The next few chapters discuss our commensal relationships with specific categories of animals. Chapter 4 discusses mesomammals—mammals too large to fit in the tiny crevasses of our homes, but not large enough to be physically threatening. He begins with cats. While cats are now largely domesticated, living among us as companion or feral animals, this was not always the case. Archaeological records tell of a time in which the ancestors of domestic cats were opportunistic feeders who began to approach human settlements seeking food and refuge. O’Connor traces the first records of cats to the Middle East. Next, he discusses dogs, which today are almost exclusively domestic or feral. However, this was not always the case. Predating domestication was commensalism, as wolves who eventually evolved into modern day dogs took up residency near human settlements. What is unique about cats and dogs is that at some point, humans accepted these animals into their domestic spaces and engaged in partnership with them. They evolved from wild to commensal to domestic. This is not the case for all mesomammals, however, many of which still engage in commensalism and may have only recently begun to do so. For example, O’Connor discusses raccoons and coyotes who have taken a liking to human settlements in North America. He also addresses the long and complex history of human-fox interactions in the UK, where he lives, and the role of monkeys as both sacred and pests in many topical locations.
               Chapter 5 describes rodents, animals who are closely associated with human settlements, although in some cases, only recently. O’Connor argues that our familiarity of rodents leads us to take them for granted and neglect and underrate them.  Humans have been associated with rodents for millennia. Rodents have been very successful hitchhikers, following humans to remote islands and the far reaches of the North and South. However, in many places, rodents are fairly new. For example, mice likely did not arrive in North America until the 1700s, when they came on the ships of European settlers. Rats reached the New World a bit earlier, around the time of Columbus in the late 1400s. Rats and other rodents are intelligent, social, adaptable omnivores that have been widely successful as commensal species. Our relationships with rodents have become increasingly complex. We have adopted them as involuntary subjects of research and sometimes companion animals. However, the majority of rodents still remain in a commensal relationship among us, adapting to the human environment and taking advantage of opportunities for food and shelter. O’Connor concludes this chapter by discussing squirrels, masters of adapting to the human environment in North America and now, Europe.
               Chapter 6 discusses another category of animals that have long engaged in commensal relationships with humans: birds. Among the most prominent are pigeons. Pigeons have many characteristics advantageous to commensalism. They can breed year round and rapidly. They are omnivorous. They can feed successfully in large flocks. Although pigeons are known to be great flyers, they tend to live sedentary lifestyles. Our relationship with pigeons is complicated, however. As opposed to cats and dogs, whom we have welcomed into our homes, pigeons have been treated as pests. They have been criticized as being a nuisance and carrying disease. O’Connor is skeptical of these criticisms, however, arguing that pigeons are not as harmful as they are portrayed and perhaps, those that benefit the most from these depictions are involved in pest control, a multi-billion dollar industry! In addition to pigeons, O’Connor discusses several other birds who humans have longstanding commensal relationships with, including sparrows, corvids (crows and ravens), and to some extent, starlings.
               In the final two chapters, O’Connor revisits the major themes of the book and discusses the future of commensalism and where we go from here. He describes commensalism as a form of coevolution between humans and nonhumans—we have influenced one another and evolved together. He also discusses how we view commensal animals is highly specific on culture as well as individual. Some may see a particular animal as sacred while others see the animal as a pest. Finally, he emphasizes that commensalism is not a species trait, but a population trait. Select groups of animals have coevolved with us, while other members of that species may have maintained their wild status.
               So where do we go from here, he asks. In this book O’Connor examines the past and present of commensal species. What about the future? He responds that as humans continue to further alter the global environment, commensalism will only become more prominent and important. If we hope to have interactions with and benefit from our neighboring animals, we will need to learn how to live with them. He argues that we need to think about how to include commensal species when designing and maintaining our environment, as they need spaces, too. Finally, O’Connor calls upon academics to study our commensal neighbors to understand how we can successfully incorporate them into an increasingly modified world.