CHAPTER TWO
There are some who can live without wild things, and some who cannot.
—Aldo Leopold
Almost 100 years after Lyall stepped onto Stephens Island, 8,500 miles to the north-northeast, Stanley Temple was wandering the islands of Wisconsin. Not islands surrounded by water and treacherous rocks but islands of grass (prairies, pastures, and hay fields) surrounded by row crops and forest. Temple, a professor of wildlife ecology at the University of Wisconsin–Madison, was studying birds in the quiet farm country of the rural Midwest with his graduate students. It was 1984, and Temple was interested in examining the wildlife benefits of federal and state grassland restoration projects, such as the U.S. Department of Agriculture’s Conservation Reserve Program, that help farmers replace erodible croplands with permanent grass cover. The long-term intent of the USDA program was to create more grassland habitats within agricultural expanses, in order to help improve water quality, prevent soil erosion, and provide wildlife habitat. It was an early attempt to make farming more environmentally friendly, especially for birds and other grassland species that were losing their natural habitats as agriculture expanded and intensified. The wildlife benefits of the program, however, had not been thoroughly evaluated, and Temple, a pioneer in the field of conservation biology, knew that scientific evaluation was essential to avoid the unintended consequences that often result from such initiatives.
Wisconsin has a variety of natural habitats, including grasslands and savannas in the south and forests in the north. It is also known as America’s dairy land and is heavily sprinkled with farms—dairy as well as those producing a variety of field crops. In 1984 approximately 70,000 farms covered the state—each with a farmhouse or two and multiple barns and other outbuildings. Temple started visiting some of these farms to set up his studies. As he roamed the state and its farmlands, he could not help but notice that most farms and associated grasslands were overrun with cats. Some farms were home to dozens of “barn cats” as well as free-ranging pets that roamed restored grasslands, preying on small rodents and birds in the precise habitats that farmers were being encouraged to manage for the benefit of native wildlife. Temple worried that by creating attractive nesting habitats close to farms and rural homes, restoration efforts might be luring birds to sites where they would be exposed to heavy predation—an ecological trap.
By this time, the domestic cat had been responsible for or had contributed to multiple animal extinctions on islands around the world, but little recognition or study had been given to its potential impacts in mainland areas. Temple decided to expand his research to address the specific question of how free-ranging cats were impacting Wisconsin’s rural wildlife. He unwittingly began a scientific study that would create a firestorm, resulting in events that not even Temple, no stranger to controversy, could have predicted. A contentious debate began that would culminate in demonstrations and even death threats.
Tens of millions of people in the United States feel a deep bond and connection with cats. Cats are animals with fascinating and alluring personalities, but they can be destructive to native wildlife. Wild birds and mammals, however, also have rights that do not seem to receive as much attention as the claimed rights of cats to wander freely outdoors. These birds and mammals have become the victims in the brewing war between cat lovers and the people who support native wild animals. Stan Temple’s study touched a dissonant chord. How should we deal with the animals that people have domesticated and enjoyed as beloved companions for thousands of years, but that when allowed to become feral or to freely range are capable of tearing away at the tapestry of life that has evolved since time immemorial?
Known as the Fertile Crescent, the area now composed of Iran, Iraq, Kuwait, Saudi Arabia, Bahrain, Turkey, and parts of Egypt, is considered the cradle of human civilization. Ten thousand years ago, it was the site of the first cultivation of agricultural crops such as wheat, barley, and lentils and the domestication of animals such as cows, goats, and pigs. Water was also beginning to be contained for drinking and irrigation there. The combination of carbohydrates, proteins, and water, along with their associated storage structures, allowed for complex human societies to evolve. As we see today in places like rural Wisconsin, such human developments attracted wildlife—including various species of granivorous mammals like the House Mouse (Mus musculus) and birds such as the House Sparrow (Passer domesticus)—that colonized structures and consumed grains. Known as peri-domesticated animals, because they thrive in close proximity to humans (peri- meaning “near”), these species can form new and complex food webs that sustain a diverse array of species, from plants to insects to mammals. It is thought that the surplus of mice and birds brought on by this convergence of events eventually led to the evolution of the domestic house cat somewhere in the Fertile Crescent. Exactly where this happened is not clear. However, cat skeletons have been found in close association with humans in ceremonial burial sites on the island of Cyprus, confirming that there was a close association with humans and cats as far back as 9,500 years ago.
Globally, there are forty native cat species in the family Felidae, indigenous to all continents except Australia and Antarctica. Most familiar are the large cats—Lion, Cheetah, Leopard, Jaguar, Snow Leopard, Cougar (Puma), and Tiger. The remaining species, all smaller, are the African Golden Cat, Andean Mountain Cat, Chinese Mountain Cat, Asian Golden Cat, Bay Cat, Bobcat, Black-footed Cat, Canada Lynx, Caracal, Clouded Leopard, Eurasian Lynx, Fishing Cat, Flat-headed Cat, Geoffroy’s Cat, Kodkod, Jaguarundi, Jungle Cat, Iberian Lynx, Leopard Cat, Marbled Cat, Margay, Pallas’ Cat, Pampas Cat, Ocelot, Rusty-Spotted Cat, Sand Cat, Serval, Iriomote Cat, Oncilla, Colocolo, Pantanal Cat, and the Wildcat (Felis silvestris)—the progenitor of the newest and most controversial species of feline, the Domestic Cat (Felis catus). The Wildcat forms a complex group composed of at least twenty distinct subspecies including, for example: Felis silvestris silvestris (European Wildcat), F. s. lybica (Near Eastern Wildcat), F. s. ornata (Central Asian Wildcat), F. s. cafra (Southern African Wildcat), and F. s. bieti (Chinese Desert Cat). All are quite similar morphologically and genetically. The European Wildcat weighs between five and twelve pounds (depending in part on the sex), is gray with mackerel dark stripes, and, aside from being on the bulky side, has a face and body quite similar to any street-smart tabby (fig. 2.1). In fact, the European Wildcat is often mistaken for a feral domestic cat. Because of the European Wildcat’s long history of interaction with feral cats, only a few of the remaining populations—hanging on in locations in Scotland, Switzerland, France, and Germany—are thought to remain genetically pure. In some places, such as northern and western Scotland, the number of pure wildcats that persist, if any at all, is unknown. The primary cause of the European Wildcat’s decline was initially deforestation, but now inbreeding with feral domestic cats and contraction of the diseases they carry are considered the primary drivers. This is all somewhat ironic because this subspecies of the Wildcat, while genetically distinct, is considered one of the ancestors of today’s domestic cat.
Recent genetic studies corroborate the notion that today’s domestic cats evolved from several subspecies of wildcats and suggest that, of the five, the Near Eastern Wildcat (F. s. lybica) is likely the domestic cat’s nearest relative. This also confirms the hypothesis that domestication of the cat occurred somewhere in the Fertile Crescent. Today, the domestic cat, largely due to selective breeding by humans and some genetic drift, has evolved into somewhere between forty and ninety different breeds. The count depends on the official cat registry that is consulted—for example, the registry of the Cat Fanciers’ Association (CFA). A “breed” or “variety” is a group of animals within a species that share a suite of characteristics. If individuals from within a breed are bred together, including through selective breeding by humans, their progeny will retain the same characteristics because of the genetic underpinnings of their traits. Some of the cat breeds are as dissimilar as a Tiger and Lion and many look nothing like the ancestral Wildcat. They may be broadly classified as short-haired or long-haired breeds. Of the short-hairs, the varieties are as distinctive as the long-necked and ruddy-colored Abyssinian, the hairless Sphynx, and the smallest of the breeds, the Singapura. The long-haired breeds are equally varied and include curly-haired varieties such as the Selkirk Rex, the flat-faced Persians, and, the largest of all, the Maine Coon. Despite the impressive variation we see across the breeds of cat, it does not come close to what we see in dogs—160 to 400 breeds, again depending on the registry. Dog breeds include those as varied as Afghan Hound, Bulldog, Dachshund, Giant Schnauzer, Great Dane, Greyhound, Doberman Pinscher, Bernese Mountain Dog, and Chihuahua. The large variety in dog breeds has arisen because dogs have been bred by humans for much longer, perhaps even 1,000 years longer, than cats and for several purposes—to hunt, herd, and smell, to name a few. Cat breeding is a more recent phenomenon and has largely been done for cosmetic purposes by cat fanciers. Nevertheless, the initial domestication of the cat likely occurred simply through the accidental merging of several events.
In the way that Black Bears moved to foraging in garbage cans and White-tailed Deer to soft, lush (and seemingly the most desirable and expensive) plantings in people’s yards, individuals from the various subspecies of the Wildcat probably went to locations where humans stored seeds, grains, and other food—locations that attracted rodents and birds. In this way cats and humans converged—in a relationship called commensalism—and this proximity, along with the fact that some individual cats were probably not as wild as others and thus were more tolerant of humans, led to the animal’s domestication. Recent research now demonstrates that there may be a genetic basis for this “tolerant” or “tame” behavior. Cats with greater access to human-provided resources likely bred more successfully and, ultimately, produced a more human-tolerant breed of wildcat. Of course, it is equally plausible that early humans simply captured cats, alluring as they are, and tamed them into pets over many generations. No one really knows how it happened, and more than likely it was some combination of the above phenomena. What we do know is that descendants of these tamed cats spread, with human assistance, to almost every corner of the globe. They were tolerated by their human neighbors because of their supreme pet-like characteristics—soft fur, cuddliness, playfulness—and their uncanny ability to prey on and suppress the numbers of small animals considered pests by their owners.
When cats first arrived in New Zealand and Wisconsin, on thousands of islands in between, and elsewhere (except Antarctica) varies. But their initial spread was almost certainly linked to the movement and settlement of Europeans. Whether cats were brought as pets or mousers, or were simply stowaways on ships, is equally mysterious, although again, more than likely, it was a combination of all of the above. Edward II (1327–1377) has been cited as requiring all English vessels to have a cat on board for pest control, and this practice almost certainly contributed to the animal’s global spread. The exact date cats arrived in the New World is not known, although they were apparently present by the second voyage of Columbus (1493–95). Cats were eaten by starving settlers in Virginia’s Jamestown Colony in the early 1600s, and they are noted in historical accounts through the 1700s. Domestic cats have been in North America for at least 500 years, if not longer, and their spread, through both the unintentional and intentional actions of humans, earns them status as one of the most successful invasive species on earth. Their movement west across the United States, and to the state of Wisconsin, is another unknown. The first documented interaction between Europeans and North American Indians in Wisconsin came when Jean Nicolet arrived in 1634 to broker a peace deal between the Huron and Ho-Chunk nations. However, at that time, Native Americans kept dogs, and there is no record of cats making the trip. Trappers and traders continued to move throughout Wisconsin over the next 150 years, but it was not until the early 1800s that farming families from Europe and the eastern seaboard began homesteading the state and changing the landscape from prairies and savannas to pastures and croplands interspersed with farmhouses and woodlots. The arrival of Felis catus into Wisconsin from the east, either intentionally or unintentionally, likely occurred sometime during the initial European immigration into the area in the early 1800s. Within a few generations of their introduction, cats were there to stay.
Stanley Temple is the Beers-Bascom Professor Emeritus in Conservation at the University of Wisconsin–Madison, as well as a senior fellow at the Aldo Leopold Foundation. He stands six feet tall, has a salt and pepper beard, wears glasses, and looks like a quintessential academic (fig. 2.2). Though Temple is soft-spoken by nature, his contributions to the field of conservation biology speak loudly. Temple has three degrees in ecology, a BS, an MS, and a PhD, all from Cornell University. His work has focused on the recovery of rare and endangered species. Temple spent thirty-two years as a professor at Wisconsin, in the same position held previously by none other than Aldo Leopold, who is considered the father of wildlife management. Leopold was the author of many scientific papers, popular articles, and, of course, A Sand County Almanac. Leopold’s classic book, published in 1949, shortly after his death, was the culmination of his life’s journey as a conservationist. It has sold millions of copies and has been translated into twelve different languages. Leopold decried the growing detachment between humans and all things wild and promoted the idea that our relationship with the natural world should be guided by ethical considerations. This notion motivated Temple as well.
Stanley Temple stepped humbly into Leopold’s shoes, and over his academic and research career he has promoted Leopold’s broad vision while focusing primarily on rare and declining birds. Temple and his students have helped save several bird species from extinction. He has written more than 320 papers and seven books, advised fifty-two master’s candidates and twenty-three PhD students, and has won multiple professional and teaching awards. Quietly and thoughtfully, Temple has become one of the premier biologists in what was, at the start of his career, the emerging scientific field of conservation biology. His research on the biology of endangered species, his design and execution of recovery efforts, and his contributions to natural resource policy are some of his lasting contributions. His work with the Peregrine Falcon (Falco peregrinus), an endangered species that Temple studied early in his career, contributed to the species’ rebound and eventual removal from the U.S. endangered species list. When he arrived on the island of Mauritius just a month after completing his PhD at Cornell, there were only seven remaining Mauritius Kestrels (Falco punctatus) in the wild—today there are 800. He helped launch decades of conservation work that helped save several species—including endemics—from extinction on the island. Halfway around the world, Temple and his students worked to save the endemic endangered Grenada Dove (Leptotila wellsi) on the island of Grenada and launched a recovery project for the species that included naming the dove the national bird. Closer to home, Temple and his students helped contribute to the development of techniques for the captive rearing, reintroduction, and eventual recovery of the California Condor (Gymnogyps californianus). Few living scientists have such a résumé.
Even as a child, Temple had a burning passion for watching and identifying birds and other wildlife. His mother, who did not share that passion, recognized her son’s craving and allowed young Stan much freedom to explore nature on his own. She sent him on field trips with the Audubon Society of the District of Columbia to places like Hawk Mountain in Pennsylvania and the Maryland coast—both regional birding hot spots, especially during migration. As fate would have it, these birding trips were also attended by a scientist and nature writer named Rachel Carson, who took a special interest in the young Temple (fig. 2.3). Carson had already written an award-winning book, The Sea Around Us (which had been made into an Oscar-winning natural history movie in 1953), and likely was beginning research for what would be her signature contribution to the environmental movement, Silent Spring. Carson, like Leopold, had a deep love for nature, a desire for its preservation, and a commitment to communicating, through accessible and beautiful prose, why natural areas and the species they contain are essential to human life. Originally entitled Man Against the Earth, the book Silent Spring spoke to the dangers and impacts of the unregulated use of pesticides, specifically DDT (dichlorodiphenyltrichloroethane), on birds and other animals. Almost as important, this book was an indictment against the denial of scientific facts. Temple, by then a high school student working at the Cleveland Museum of Natural History, with a growing interest in birds of prey and conservation science, took notice when his inspiring mentor published Silent Spring in 1962. As a pesticide like DDT moves up a food chain—passed from plants to herbivores to predators of those herbivores—its concentrations tend to increase, through a process called biomagnification. Because birds of prey often consume herbivores and mid-level omnivores, they are prone to concentrate such pesticides, and by the 1960s they were becoming severely impacted by DDT. Populations of species such as the Bald Eagle, the Peregrine Falcon, and the Osprey were plummeting. Temple, influenced by two giants in the field of environmental science—Leopold, whom he never met but whose ethics profoundly influenced him, and Carson, who quietly and thoughtfully provided mentorship—was destined to tackle similar abuses against the earth in an effort to avoid the future silencing of our springs.
It took a long ten years after the publication of Silent Spring for DDT to be banned from use in parts of the United States. The delay was due largely to confusion manufactured by the deliberate misinformation disseminated by large corporate pesticide interests. Wisconsin was the first state to ban DDT’s use. In June 1972 William Ruckelshaus, the first administrator of the newly created Environmental Protection Agency, announced the national banning of DDT, although it was still used sporadically around the United States until 1979. Like many other environmental contaminants, DDT still persists in nature, and to this day birds in some regions are still suffering from toxic levels of this pesticide.
Invasive species are, on one level, simply another form of an environmental contaminant; like DDT, they can cause great harm and, once introduced, can be exceptionally difficult to remove from the environment. The domesticated cat is one of the earliest invasive animal species on the planet, perhaps following closely behind only the House Mouse and the Black Rat (Rattus rattus). These two rodent species, indigenous to Asia, are transported by humans and considered cat prey. To be considered as an invasive species, the plant or animal, whose movement is assisted by humans, must be nonnative to a particular location and to spread like wildfire there, causing ecological damage to native species and the habitats they occupy. In some cases, invasive species can also impact human health—sometimes fatally—and wreak havoc on local and national economies. Think of Asian Tiger Mosquitoes (Aedes albopictus) carrying dengue and West Nile viruses, or of the common European Rabbit (Oryctolagus cuniculus) overgrazing massive areas of Australia’s Outback and the South Island of New Zealand.
When an invasive species first settles and starts to reproduce and disperse in a new ecosystem, it needs to either occupy an available niche or outcompete a niche’s previous inhabitant to be successful. Domestic cats have been successful on both counts—occupying a broad geographic reach and outcompeting previous niche inhabitants—while exponentially reproducing. In fact, it is this collective impact that now puts Felis catus on the list of the world’s 100 worst invasive alien species. The animal’s success as an invasive species was understood long before Temple started to study the impacts of rural cats in Wisconsin. In fact, the success had been illustrated unambiguously on islands (such as Stephens Island) and on wildlife—specifically birds.
Approximately 180,000 islands exist on earth. They vary in size and shape, in the amount of vegetation, and in their elevation. They include continental islands, such as Greenland, Great Britain, and Madagascar—which lie on the shelf of a nearby continent—and oceanic islands, typically much smaller and of volcanic, tectonic, or coral origin (tropical islands). Because of their geographic isolation, islands share high levels of species endemism and biodiversity. Unfortunately, they also share high rates of species extinctions and/or declines in the population sizes of the endemic species they harbor. These rates are higher on smaller or midsize islands. Species with limited or no flying ability—like the Stephens Island Wren—are particularly vulnerable. Island species evolved with few to no predators, and as a result most have limited or no escape mechanisms. So, when a cat, rat, or mongoose—all extremely effective predators—makes it to an island, it is just a matter of time before significant population declines or extinctions of island fauna occur. To date, it is estimated, cats have been brought to about 10,000, or 5 percent, of the islands on earth.
In an article published in the journal Global Change Biology, Felix Medina and coauthors reviewed studies conducted on approximately 120 different islands around the globe of the impacts cats have had on endangered insular vertebrates. They concluded that cats have caused a population decline, a reduction in geographic distribution, or an extinction in 175 species of reptiles, birds, and mammals. Among reptiles, twenty-five species of iguanas, lizards, turtles, and snakes have been negatively impacted. In total, 123 species of birds have been negatively impacted, including songbirds, parrots, seabirds, and penguins. Among mammals, twenty-seven species—primarily rodents and marsupials but also a species of bat and even a lemur from the island of Madagascar—have been negatively impacted by cats. Overall, the domestic cat has contributed to or caused thirty-three (14 percent) of the 238 global reptile, bird, and mammal extinctions. Medina et al. concluded that this likely is an underestimate due to the lack of monitoring and research on most islands—especially in places known for high species endemism as well as a sizable presence of cats, including islands of Asia, Indonesia, Polynesia, and Micronesia. For comparison, there are no confirmed bird extinctions from the pesticide DDT.
Some of the thirty-three species whose extinctions are attributed to cats are still warm. Two of the twenty-two bird taxa include the Socorro Dove (Zenaida graysoni), last confirmed in the wild in 1972 (fig. 2.4), and the Hawaiian Crow (Corvus hawaiiensis), last encountered in 2002. Both species are different from the other thirty-one in that, although they are technically extinct in the wild, they are not fully extinct; individuals of both species were brought into captivity at various times and bred. Captive breeding, the removal of threats that drove these species to extinction in the wild, and the careful release and monitoring of individuals would need to happen if these species were to be successfully reestablished in the wild—approaches much like those Stan Temple took in his work with the Mauritius Kestrel and the California Condor. Each of these island extinctions is a story in itself, and cats were involved either directly or indirectly in the demise of each of the species in the wild. Retracing the steps of one such species’ disappearance is helpful for those wishing to avoid similar disasters in the future.
Isla Socorro is one of the four Revillagigedo Islands lying off the southern tip of Baja California, just beyond the continental shelf in the Pacific Ocean. The archipelago is of volcanic origin, and its unique ecosystem supports at least sixteen endemic vertebrate taxa, all birds and reptiles. No native mammals occur on the islands. The island of Socorro has the richest biodiversity, including the aforementioned Socorro Dove as well as seven other species of endemic birds. Since 1867 there have been numerous expeditions to Socorro to survey its unique flora and fauna. One included Bayard Brattstrom, a UCLA PhD student who visited the islands in 1952 and published his findings four years later in the ornithological journal The Condor. One passage from his paper is almost prophetic:
The future of the avifauna of the islands appears to be secure at present. There are no human inhabitants, and no mammals of any kind except the moderate and apparently stable population of sheep on Socorro. Few ships stop at any of the Revillagigedo Islands, and the birds are seldom molested. The remote location and generally barren aspect of the archipelago have so far protected its biota from all except volcanic destruction. While this fortunate condition still exists, it may be hoped that the Mexican government will guard against the introduction of mammals such as rabbits, cats, goats and others that have invariably brought disaster to the flora and fauna of insular regions.1
Sadly, something did bring disaster to this small island after Bayard’s 1956 observations. In March 1972 the state of Colima organized an expedition to Socorro Island to celebrate the 100th anniversary of Benito Juárez, a reform-minded politician who had served five terms as president of Mexico. The state of Colima was actually considering renaming the island in honor of Juárez. A published account of those festivities (Velasco-Murgía, 1982) provided the last scientifically credible sighting of the Socorro Dove in the wild. Velasco-Murgía noted that several visitors were seen killing the tame Socorro Doves with sticks, for no apparent reason. The Mexican ornithologist Juan Martínez-Gómez, who has spent most of his career studying the birds and their recovery on the Revillagigedo Islands, has since interviewed Mexican military personnel once stationed on the island, and although these are records by non-ornithologists, they suggest the Socorro Dove may have been seen as late as 1975. However, subsequent expeditions in 1978 and 1981 by Joe Jehl, Ken Parkes, and a returning Bayard Brattstrom failed to locate any individuals of the species. From what appeared to be a healthy population in the 1950s to the last survivors in the early to mid-1970s—the endemic doves of Socorro Island met a terrible fate.
Species extinctions are more often than not caused by multiple, cumulative, and interacting factors. While Jehl and Parkes found signs of feral cats throughout Socorro Island (cats were thought to have been brought to Socorro when a military installation was established in the late 1950s), and evidence implicated cats as preying on island endemics, subsequent research and interviews by Juan Martínez-Gómez failed to find convincing evidence that cats were on Socorro Island much earlier than 1970. Post-1972 Martínez-Gómez, while studying the endangered Socorro Mockingbird (Mimus graysoni), confirmed the presence of feral cats and their impacts. He identified body parts (feathers) of several endemic endangered bird species, including the Socorro Mockingbird and the Townsend’s Shearwater (Puffinus auricularis) in cats’ scat and stomachs. There is little question that feral cats contributed to the decline and eventual extinction of the Socorro Dove. But the degree of their responsibility remains unclear.
Martínez-Gómez postulates that the problem may have started in 1869 when sheep were first introduced to the island and eventually allowed to go feral. Their impact on the native vegetation, although not quantified, is indisputable. Over the next seventy-five years, visiting scientists, including Brattstrom, commented on the innocuous nature of the sheep population, but it was clear that the island’s sensitive and critical habitat was undergoing a slow, cumulative change. Substantial overgrazing was triggering changes to the vegetation that would likely go unnoticed by the casual observer but certainly impacted birds like the Socorro Dove and Mockingbird, which were dependent on plants for food and cover. It is likely both species began to decline as soon as sheep were introduced. The decline accelerated just a few years after cats arrived. Because there were never any systematic monitoring schemes in place, it remains impossible to chart how quickly the decline actually happened. Socorro Doves were known to be particularly tame and were easy prey for cats and the occasional human with a battering stick. With an absence of cover, the dove had few places to hide, and remaining individuals were likely quickly dispatched by the growing feral cat population—much like what happened to the Stephens Island Wren. Thankfully, unlike the wren, Socorro Doves had been captured earlier in the twentieth century and bred in captivity. An eventual release back into the wild, once cats and sheep are finally removed from the environment, seems imminent. Whether the doves—like Stan Temple’s Mauritius Kestrels—will be successful remains unclear.
Temple had been observing bird species flicker on and off the planet throughout his career. The specter of yet another invasive species wreaking havoc with birds was now before him in his home state of Wisconsin, as the number of free-ranging cats continued to increase. Temple was well aware of the strong evidence that implicated cats as a cause of species declines and extinctions on islands, and now he was seeing troubling numbers of these introduced predators in habitats surrounding farms and rural homes throughout Wisconsin. In many cases, these rural dwellings abutted grassland habitats containing species experiencing sharp declines, such as Eastern Meadowlark (Sturnella magna), Bobolink (Dolichonyx oryzivorus), and Henslow’s Sparrow (Ammodramus henslowii). Temple knew it was time to collect data on the impact of cats on bird populations across the state and then, as a good conservation biologist, educate the public about the results, whatever the outcome. He secured funding from the USDA and the Wisconsin Department of Natural Resources, two government agencies that were promoting the creation of grassland habitats on farms to benefit declining wildlife.
Temple and his graduate student, John Coleman, set out to build a quantitative model, a necessary exercise if one hopes to understand some aspect of a complex system especially over a large spatial scale. Quantitative models are used in almost every aspect of science, in business, and even in everyday life; they simply vary in the complexity of their makeup and the uncertainty of their outputs. An example of a simple modeling problem might be to try to determine the cost of gasoline you would need to drive a car the length of the state of California. To determine this you need to know: (1) the average cost of gasoline, (2) the average miles per gallon for your specific make and brand of car, and (3) the length in miles of the state of California. Each of these estimates or “variables” has some degree of uncertainty. For example, the cost of gasoline will vary from station to station; the fuel efficiency will depend upon the speed driven, traffic, and the driver; and the exact miles driven will not be known until the end of the trip, making even this an estimate plus or minus some number of miles. The uncertainty can be estimated as well, so you know how much confidence you have in the final amount of money to put aside for your gasoline budget. In Temple and Coleman’s case, the central question was straightforward—how many birds do cats kill each year across the rural areas of Wisconsin? The variables in the model were also fairly simple. First: how many free-ranging outdoor cats are there in rural Wisconsin; and second: how many bird kills per cat are there per year? Their model looked like this:
(number of rural cats) × (number of bird kills/rural cat/year)
To estimate the first variable—how many rural free-ranging cats are in the state of Wisconsin—they started off with the names and addresses of roughly 130,000 rural Wisconsin residents enrolled in the USDA’s Agricultural Stabilization and Conservation Program. Almost all farmers and many non-farm rural homeowners were enrolled in this program, so this list ensured excellent coverage across the state. They then randomly selected 1 percent of potential respondents from this list, sampling from each of the seventy-two Wisconsin counties to ensure their results would be representative of all residents. A survey of twenty-two questions, along with a cover letter assuring anonymity, was then mailed to 1,324 Wisconsin residents on April 13, 1989. By November of that year, after sending reminder postcards and making a few phone calls, Temple and Coleman received about 807 usable responses—a 64.4 percent response rate. From these responses they determined that about 80 percent of respondents had between one and sixty cats (average of about five) and that the number of cats varied, depending on whether it was a farm or not and the type of farm. Livestock farms, for example, had up to nine cats on average. Temple and Coleman then took their data on cat density per type of rural residence and estimated the cat densities across the state. They came up with an estimate of 1.4 to 2 million free-ranging cats in rural Wisconsin. This equates to an average density of ten to fourteen cats per square kilometer (about 250 acres). These were essential estimates for developing the model and for better understanding the scale of the issue for bird populations. The researchers then had to determine how many kills were made per cat and how many of these were birds. This required capturing cats and collaring them with radio transmitters, so Temple and Coleman could measure several aspects of their behaviors.
Several studies had already been published estimating the number of kills an individual cat will make per year. Estimates indicated a range from zero to many more than a cat could possibly consume (one rural cat was recorded to have killed 1,690 animals over an eighteen-month period). Temple and Coleman used a variety of techniques to determine what cats were eating, including directly observing eleven radio-collared cats over 526 hours, analyzing the contents of 768 deposits of cat feces, and making 130 live-captured cats regurgitate their recently consumed prey with the use of harmless emetics. Cat owners participating in their study also reported 279 observations of their cats killing prey. Combined, these data revealed, as Temple and Coleman had suspected, that small birds and small mammals, such as rodents and rabbits, were typically the most common prey of free-ranging cats. Other studies using similar techniques have demonstrated that cats are generalized and opportunistic predators—they will kill anything that moves and is within their size range. Sometimes they will eat their prey and sometimes they will not—because of this variability Temple and Coleman considered it essential to combine as many types of studies as possible to develop their model estimates. Incorporating a literature review with their own data, they concluded that birds make up somewhere between 20 and 30 percent of the diet of free-ranging cats. The two researchers plugged the range of numbers from each of their components into the models and made their computations. They determined that rural free-ranging cats in Wisconsin kill, at a minimum, 7.8 million birds annually (at least 1.4 million cats times at least 5.6 birds killed per cat per year). Given that the densities of free-ranging cats in some areas of rural Wisconsin were several times higher than the typical combined densities of other midsize predators, such as foxes, skunks, opossums, and Raccoons, free-ranging cats clearly represented a major predator of native birds in rural Wisconsin. But what did these numbers mean?
Temple once again built a fairly simple model. He had detailed tracking data on cats, so he knew the typical size of a given animal’s home range and the specific habitats where cats hunted. Bird censuses had been done in these habitats, so he also knew how many birds were present and available in each acre of habitat and within the average hunting range of a cat. What he concluded was that a minimum of 10 percent of small- to medium-size birds living within each cat’s hunting range were typically lost to cat predation—a fairly significant take.
Most academic papers are read by peers at other universities and filed away to be periodically reviewed by other researchers exploring similar topics. But when Coleman and Temple’s preliminary report was published in 1989, in the Fourth Eastern Wildlife Damage Control Conference program, and a longer report was published in 1993 in Wildlife Society Bulletin, the story reached the general public. Cats, it seems, are catnip for journalists. “I had no idea simply uncovering the facts would touch such a raw nerve with cat activists,” Temple said many years later. “It was tough dealing with the nasty calls and ugly hate mail.”2 Temple even received death threats, after a newspaper article inaccurately implied that cats had been killed so their stomach contents could be analyzed. No cats were harmed in the course of the Wisconsin study, although some radio-collared cats did die from diseases and accidents. (Temple would receive more hate mail and death threats in 2005 when Wisconsin considered legislation that would essentially legalize the hunting of free-ranging cats—more on that later, in chapter 6.) All this uncivil discourse revealed a surprising disconnect: Many Wisconsinites (at least those who wrote letters to the editor and hate mail to Temple) were much more concerned that cats were being blamed for songbird deaths than with the fact that millions of songbirds were being killed. And some were more troubled about the possibility of cats being killed than they were about the life of a researcher.
Stan Temple actually likes cats and has owned several, which he keeps inside his rural Wisconsin home. He places value on his pets and knows they are safer indoors. But he also sees value in the lives of the songbirds and other wildlife species that are native to the land surrounding his home. More and more people are valuing birds and swelling the ranks of bird-watchers. Likewise, there are more cat owners in America now than at any time in history. But far fewer people, it seems, can summon affection for both cats and wildlife—and empathy for those they perceive to be on the “other side.” As each side has swelled in numbers, the stage has been set for “bird people” and “cat people” to square off, forgetting, perhaps, that they are all animal lovers in the first place.