Prairie dogs and the grassland habitat in which they play a key ecological role have declined precipitously over the past two centuries. The currnumber of prairie dogs is believed to be less than 2 percof the number encountered by Lewis and Clark in the early 1800s, and only a fraction of grassland ecosystem remains. Conservation of the Black-Tailed Prairie Dog offers specific information to help scientists and managers develop rigorous plans for ensuring the long-term survival of the prairie dog and its habitat. With contributions from thirty leading biologists who are actively working to save prairie dogs, the book addresses a range of pivotal issues including: the ecology and social behavior of prairie dogs; the prairie dog's role as a keystone species; factors that have led to drastic population declines; practical solutions for protecting the prairie dog and its grassland ecosystem; and concerns of farmers and ranchers who view prairie dogs as a nuisance and a threat to their livelihoods Extensively illustrated with tables, figures, photos, and charts, and thoroughly referenced with more than 700 citations, the book is a unique and vital contribution for anyone concerned with prairie dogs, prairie dog conservation, or the conservation and managemof grassland ecosystems.
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About the Author
John L. Hoogland is a Professor of Biology at the University of Maryland's Appalachian Laboratory and has studied prairie dogs for the last 33 years.
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Conservation of the Black-Tailed Prairie Dog
Saving North America's Western Grasslands
By John L. Hoogland
ISLAND PRESSCopyright © 2006 Island Press
All rights reserved.
Introduction: Why Care About Prairie Dogs?
John L. Hoogland
Black-tailed prairie dogs—hereafter, simply "prairie dogs"—are burrowing rodents that inhabit the grasslands of western North America. Coloniality is perhaps the most striking feature of these plump, brown, non-hibernating, herbivorous squirrels that stand about 30 centimeters (12 inches) tall, weigh about 700 grams (1.5 pounds), and forage aboveground from dawn until dusk.
Whether or not one likes prairie dogs, they are hard to ignore. Their colony-sites sometimes contain thousands of residents and extend for kilometers in all directions. The vegetation at colony-sites is unusually short, because prairie dogs systematically consume or clip grasses and other herbs that grow taller than about 30 centimeters (12 inches). Colony-sites contain hundreds of large mounds—as high as 0.75 meter (2.5 feet) and with a diameter as great as 2 meters (7 feet)—that surround most burrow-entrances.
After emerging from their burrows at dawn, prairie dogs forage, fight, chase, "kiss," vocalize, and play aboveground until they submerge for the night at dusk. Prairie dogs thus differ markedly from other burrowing mammals, such as pocket gophers and moles, which people rarely see. Further, colony-sites foster the growth of plants such as black nightshade, fetid marigold (also called prairie dog weed), pigweed, and scarlet globemallow—all of which are uncommon away from colony-sites. Finally, colony-sites attract fun-to-see animals such as American badgers, American bison, black-footed ferrets, bobcats, burrowing owls, coyotes, ferruginous hawks, golden eagles, mountain plovers, prairie falcons, pronghorn, and swift foxes.
About 200 years ago, prairie dogs inhabited eleven states, Canada, and Mexico, and their numbers probably exceeded five billion. As pioneers moved west, however, they often viewed prairie dogs as pests. Ranchers observed the reduced amount of grass at colony-sites and logically deduced that prairie dogs must compete with their livestock for food. Ranchers also concluded, again logically, that their livestock would incur leg fractures after stepping into prairie dog burrows. Farmers learned that the large mounds at burrow-entrances impede plowing and the growth of crops, and that prairie dogs sometimes eat crops.
Often with assistance from local, state, and federal agencies, ranchers and farmers have shot and poisoned billions of prairie dogs, or have converted prairie dog habitat to farmland. More recently, plague (a disease introduced into North America from Asia) has killed millions of prairie dogs, and urban development has eliminated some of the best prairie dog habitat. The current number of prairie dogs is less than 2% of the number that Meriwether Lewis described as "infinite" 200 years ago (Burroughs 1961).
Because of the drastic decline in numbers of prairie dogs over the last two centuries, the United States Fish and Wildlife Service (USFWS) concluded in 2000 that the prairie dog was a candidate species (i.e., was under consideration for the Federal List of Endangered and Threatened Wildlife and Plants (FLETWP) (Chapter 12). In 2004, USFWS reversed this decision by concluding that the prairie dog is no longer a candidate species (Chapter 12). Regardless of technical designation, the inescapable conclusion is that prairie dog populations have declined sharply over the last 200 years and are still victimized today by recreational shooting, poisoning, plague, and elimination of habitat.
"So what?" you might say. Should we care that the prairie dog, once so common, now occurs at less than 2% of its former numbers? The answer, I think, should be yes, as briefly outlined below and as further explored in the next 17 chapters.
Many people think about problems in terms of dollars and cents, so let's talk first about the finances regarding prairie dogs. Since poisoning began in the late 1800s, thousands of people per year have worked together to eliminate prairie dogs, with a cumulative cost of billions of dollars (Chapter 8). But the financial costs of eradication often exceed the benefits (Chapters 5, 8 and 9), because: poisons and the efforts necessary to dispense them are expensive; colonies often repopulate quickly after poisoning; competition between domestic livestock and prairie dogs is sometimes insignificant; and livestock only rarely step into prairie dog burrows. Perhaps money used for widespread poisoning could be reallocated for financial compensation to those ranchers and farmers who lose money because of prairie dogs (Chapters 14 and 17). This solution would cost less than trying to eradicate prairie dogs, would satisfy most ranchers and farmers, and would allow prairie dog populations to recover.
Most people think that all organisms have the right to exist, and that deliberate eradication of any native species is unacceptable. Indeed, this reasoning was a major factor in the passage of the Endangered Species Act (ESA) and applies specifically to prairie dogs (Chapters 7, 17, and 18).
Every species affects other species, and this axiom is especially relevant for prairie dogs (Johnsgard 2005; Chapters 4 and 5). Via foraging and clipping of vegetation and the mixing of topsoil and subsoil during excavations, prairie dogs alter floral species composition at colony-sites. Their burrows and colony-sites provide shelter and nesting habitat for myriad other animals such as tiger salamanders, mountain plovers, burrowing owls, black-footed ferrets, and hundreds of insect and arachnid species.
In addition, prairie dogs serve as prey for numerous mammalian and avian predators, such as American badgers, black-footed ferrets, bobcats, coyotes, ferruginous hawks, golden eagles, and prairie falcons. Consequently, conservation is important not only for the prairie dogs themselves, but also for the many plants and animals that associate with prairie dogs and depend on them for survival. Many conservation biologists—probably most—are more concerned about the grassland ecosystem than about prairie dogs (Chapters 4, 12, 17, and 18).
Prairie dogs provide several direct benefits to humans. Many people, for example, enjoy watching them and the many other animals attracted to their colony-sites (Chapter 15). Further, laboratory research with prairie dogs has led to a better understanding of the mammalian kidney and of diseases of the human gallbladder (Chapter 18). By removing woody plants such as honey mesquite, and by improving the nutritive value and digestibility of certain grasses, prairie dogs sometimes improve the habitat for livestock (Chapter 5). Finally, because they are uniquely social, prairie dogs have helped researchers to understand perplexing issues such as inbreeding and infanticide that affect humans and other social animals (Chapters 2 and 3).
So, yes, I think that we should care that prairie dog populations have plummeted over the last 200 years. I also think that we must try to reverse this trend. For the conservation of prairie dogs, at least four aspects are noteworthy:
Regarding natural history, we know more about prairie dogs than we do about most other species that are on, or candidate species for, FLETWP. At Wind Cave National Park, South Dakota, for example, I studied eartagged, marked prairie dogs of known ages and genealogies for 15 consecutive years (Hoogland 1995). The prospects thus are higher than usual for using information about ecology, demography, and population dynamics to formulate realistic, promising plans for conservation.
Many endangered animals affect only a small geographic area; consequently, their impact is often localized, and sometimes almost undetectable. The prairie dog, by contrast, originally inhabited eleven states and parts of Canada and Mexico and is highly conspicuous. Its perceived impact on ranching and farming is gargantuan.
The rarity of most endangered species has resulted, incidentally rather than deliberately, from human activities such as conversion of habitat for agriculture, suppression of fire, and construction of factories and houses. These activities also have contributed to the decline of prairie dogs, but in addition there has been a calculated war with poison that has killed billions of prairie dogs over the last 100 years (Chapters 8 and 9).
The outlook for many endangered species is dim—indeed, almost hopeless. For prairie dogs, however, the potential for conservation is enormous. Chapter 16, for example, lists 84 potential sites for large sanctuaries. Chapters 5 and 9 suggest ways to minimize competition between prairie dogs and livestock. Chapter 11 tells us which areas are least prone to outbreaks of plague, and Chapter 3 emphasizes how prairie dogs have a knack for overcoming seemingly impossible odds.
The purpose of Conservation of the Black-Tailed Prairie Dog is threefold. In Part I, other authors and I summarize the biology and natural history of prairie dogs. To formulate rigorous plans for conservation, we need good information on issues such as when they breed, how far they disperse, how they affect other organisms, and how much they compete with livestock. In Part II, we summarize how poisoning, plague, recreational shooting, and loss of habitat have caused a precipitous decline of prairie dog populations over the last 200 years—so that we can correct these problems and avoid similar mistakes in the future. In Part III, we propose practical solutions that we hope will ensure the long-term survival of the prairie dog and its grassland ecosystem, and that also will be fair to landowners. We cannot expect farmers and ranchers to incur all the costs for the conservation of prairie dogs while the rest of us enjoy all the benefits.CHAPTER 2
Social Behavior of Prairie Dogs
John L. Hoogland
Investigation of an animal's social behavior tackles issues such as spacing of individuals; timing of mating, parturition (i.e., giving birth), and weaning; and how individuals defend against predators. Information on these issues is essential for good conservation (Caro 1998; Durant 2000; Moller 2000; Sutherland and Gosling 2000; Holt et al. 2002; Dobson and Zinner 2003; Gosling 2003). A recovery plan for a species whose individuals live solitarily, for example, will differ from a plan for a species whose individuals live in colonies. And translocations are more likely to be successful if we can avoid them at certain points of the annual cycle (e.g., during the breeding season, or when juvenile nutrition still results solely from suckling).
In this chapter I summarize information on the social behavior of prairie dogs. In particular, I focus on issues germane to conservation. I start by addressing taxonomy (i.e., scientific classification), so that we all can agree on the animal that we are trying to save. I also discuss methods that make it possible for ecologists like me to identify social groupings such as coteries, colonies, and complexes. I then examine the prairie dog mating system, which inevitably leads to a consideration of genetic drift and inbreeding, both of which can hinder conservation.
Taxonomy of Prairie Dogs
The prairie dog's common name is misleading, because it is not really a "dog" at all. The first part of the common name refers to its grassland habitat (Hollister 1916; Clark 1977). The second part refers to the prairie dog's alarm call, which reminded early settlers of a domestic dog's bark (Smith et al. 1976, 1977; Clark 1979).
Prairie dogs are burrowing, colonial mammals that belong to the genus Cynomys of the squirrel family (Sciuridae; Table 2.1). Other members of the squirrel family include chipmunks, flying squirrels, ground squirrels, marmots, and tree squirrels (Hafner 1984; Harrison et al. 2003).
The genus Cynomys has five similar species. Adults of all species stand about 30 centimeters (12 inches) tall, weigh 500–1,500 grams (1–3 pounds), have brown fur, and live in colonies. Key physical characteristics for identifying the different species are length and color of tail, and presence or absence of a black or dark brown line above each eye. Vocalizations are also distinctive for each species (Waring 1970; Hoogland 1995; Frederikson 2005).
Mammalogists recognize two subgroupings within the genus Cynomys (Hollister 1916; Pizzimenti 1975; see Table 2.1). The black-tailed subgroup (subgenus Cynomys) contains black-tailed and Mexican prairie dogs. The white-tailed subgroup (subgenus Leucocrossuromys contains Gunnison's, Utah, and white-tailed prairie dogs. Salient differences between the two subgroups include the following:
Mexican and black-tailed prairie dogs have long (7–10 centimeters, or 2–3 inches) black-tipped tails, but the other prairie dog species have shorter (3–7 centimeters, or 1–2 inches), white- or gray-tipped tails.
Mexican and black-tailed prairie dogs do not hibernate, but Gunnison's Utah, and white-tailed prairie dogs remain underground for about four months during late fall and winter.
Mexican and black-tailed prairie dogs live at elevations of 700–2,200 meters (2,300–7,200 feet) above sea level, but the other species live at higher elevations of 1,500–3,000 meters (4,900–9,800 feet).
Vegetation within colonies of Mexican and black-tailed prairie dogs is rarely more than 30 centimeters (12 inches) tall, but shrubs within colonies of Gunnison's, Utah, and white-tailed prairie dogs are commonly more than 50 centimeters (20 inches) tall.
Overlap of the geographic ranges of the five species is trivial, so that locality alone is diagnostic for identification (Figure 2.1).
All five species of prairie dogs are rare (Zeveloff and Collett 1988; Biodiversity Legal Foundation 1994; Hoogland 2003a). As endangered and threatened species, respectively, the Mexican and Utah prairie dogs are on the Federal List of Endangered and Threatened Wildlife and Plants (FLETWP) (USFWS 1970, 1984). Petitions to add Gunnison's and white-tailed prairie dogs as threatened species to FLETWP are pending (Center for Native Ecosystems et al. 2002; Rosmarino 2004). The United States Fish and Wildlife Service (USFWS) concluded in 2000 that the black-tailed prairie dog is a candidate for FLETWP as a threatened species, but reversed that conclusion in 2004 (USFWS 2000a, 2004; Chapter 12). In this book, other authors and I focus on conservation of the black-tailed prairie dog, the species of Cynomys for which we have the most information (Figure 2.2). Many of our arguments apply to the other four species of prairie dogs as well.
The scientific name for the black-tailed prairie dog is Cynomys ludovicianus, for which Hollister (1916) recognized two subspecies: Cynomys ludovicianus ludovicianus and Cynomys ludovicianus arizonensis. Pizzimenti (1975: 64) argued, however, that "... there is no reason to support subspecific designation...." This is an important distinction, because, if correct, it means that we need to conserve one subspecies rather than two.
Their geographic ranges are distinct (see Figure 2.1), but black-tailed and Mexican prairie dogs are remarkably similar. Black-tailed prairie dogs usually have shorter tails than Mexican prairie dogs, and only the distal one-third (versus the distal one-half) of the tail is usually black—but overlap for both of these measurements is substantial (Hollister 1916; Pizzimenti 1975; Hoogland 1996a). Classification of black- tailed and Mexican prairie dogs as separate species, rather than as isolated populations or subspecies of the same species, is somewhat arbitrary (Hollister 1916; Kelson 1949; Pizzimenti 1975; McCullough et al. 1987).
As noted above, black-tailed prairie dogs do not hibernate—even in colonies as far north as Saskatchewan, Montana, and North Dakota. In warm, sunny weather, individuals usually emerge from their burrows at about dawn and forage aboveground until about dusk. Individuals do, however, sometimes remain underground for several consecutive days during inclement weather in late autumn and winter (Koford 1958; Thomas and Riedesel 1975; Harlow and Menkens 1986; Bakko et al. 1988; Lehmer et al. 2001). Rarely, an individual or small group of individuals remains underground for a month or more during severe winter weather (Hoogland 1995). These temporary periods of underground inactivity mean that visual counts of individuals in winter will be underestimates of colony size (see also Chapter 6).
Relative to the other four species of Cynomys, the black-tailed prairie dog is the most common, the most conspicuous, and the one most likely to be found in zoos. When scientists, nonscientists, farmers, ranchers, or city dwellers use the term "prairie dog," they usually mean the black-tailed prairie dog. Similarly, other authors and I are referring only to the black-tailed prairie dog when we use the term "prairie dog" in this book.
Excerpted from Conservation of the Black-Tailed Prairie Dog by John L. Hoogland. Copyright © 2006 Island Press. Excerpted by permission of ISLAND PRESS.
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Table of Contents
ContentsAbout Island Press,
CHAPTER 1 - Introduction: Why Care About Prairie Dogs?,
PART I - Natural History of Prairie Dogs,
CHAPTER 2 - Social Behavior of Prairie Dogs,
CHAPTER 3 - Demography and Population Dynamics of Prairie Dogs,
CHAPTER 4 - The Prairie Dog as a Keystone Species,
CHAPTER 5 - Do Prairie Dogs Compete with Livestock?,
PART II - Why Have So Many Prairie Dogs Disappeared?,
CHAPTER 6 - Estimating the Abundance of Prairie Dogs,
CHAPTER 7 - Attitudes and Perceptions About Prairie Dogs,
CHAPTER 8 - Past and Current Chemical Control of Prairie Dogs,
CHAPTER 9 - Methods and Economics of Managing Prairie Dogs,
CHAPTER 10 - Recreational Shooting of Prairie Dogs,
CHAPTER 11 - Conservation of Prairie Dogs in Areas with Plague,
CHAPTER 12 - Does the Prairie Dog Merit Protection Via the Endangered Species Act?,
PART III - Conservation of Prairie Dogs,
CHAPTER 13 - Establishment of New Prairie Dog Colonies by Translocation,
CHAPTER 14 - A Multi-State Plan to Conserve Prairie Dogs,
CHAPTER 15 - Role of Federal Lands in the Conservation of Prairie Dogs,
CHAPTER 16 - Focal Areas for Conservation of Prairie Dogs and the Grassland Ecosystem,
CHAPTER 17 - A Proposal for More Effective Conservation of Prairie Dogs,
CHAPTER 18 - Saving Prairie Dogs: Can We? Should We?,
Appendix A. Common and Scientific Names,
Appendix B. Acronyms,
Appendix C. Calculations for Chapter 10,
List of Contributors,
Island Press Board of Directors,