The reason for this turnaround remains obscure, but it may have something to do with a seasonal change in the “value” of the pups. In early spring when browse is scarce, another female’s offspring may be most attractive as a source of nourishment. But by the time the pups appear above ground, their status changes abruptly from victim to defense. With her own progeny now exposed to predation, each female attempts to draw extra pups around her as protection for her own. If a predator attacks, there is a chance that her offspring will avoid harm by losing themselves in the crowd.
In the last 150 years or so, any threat posed to prairie dogs by their own infanticidal bent has been overshadowed by a greater and more persistent threat. To many cattlemen, a prairie dog colony, with its spreading expanse of close-clipped plants, represents little more than a terrible waste of grass, a view that has traditionally been seconded by range scientists. In 1924, for example, a team of respected researchers stated categorically that the prairie dog “does not possess a single beneficial food habit [beneficial to cattle, that is]; nor is there any argument . . . against its complete eradication on all grazing ranges.” With that end in mind, prairie dogs have been poisoned with bait, suffocated with gas, drowned, and shot. Thousands more have been vacuumed out of their dens so that they could be relocated or, more often, offered a “humane” death. The result of this relentless and sometimes gleeful campaign of extermination has been a 98 percent reduction in the population of black-tailed prairie dogs since 1900.
In 2000, the U.S. Fish and Wildlife Department determined that the black-tailed prairie dog merited listing as a “threatened” species under the U.S. Endangered Species Act but determined that “further action to place it on the list is precluded by actions to address higher-priority species.” Dissatisfied with this ruling, conservation groups petitioned for a new assessment in 2004 and again in 2008, resulting in the species being removed from the list altogether. (The black-tailed prairie dog is listed as a “Species of Special Concern” at the northernmost extension of its range in Canada.) Meanwhile, under state legislation, prairie dogs continue to be targeted as pests, and in some jurisdictions landowners are obligated by law to eradicate prairie dog towns, otherwise known as infestations of varmints.
All clear! The prairie dog’s “jump-yip” display signals the departure of a threat, such as a predator, from the area. Soon, all the dogs in the vicinity will join in the performance, yipping and jumping at their release from danger.
The war against prairie dogs has been based on the premise that they destroy rangelands. And it is certainly true that a prairie dog colony—with its patches of exposed ground and stumpy, chewed-off plants—bears a striking resemblance to a badly managed pasture. But recent research suggests that while prairie dogs can prevent the plants from recovering by keeping them snipped down, the rodents are rarely the primary cause of overgrazing. Because they cannot move into tall stands of dense vegetation, they can only follow where heavy grazing by cattle (or formerly bison) has opened up a path. Ranchers who overtax their rangelands have effectively laid out a welcome mat and invited the prairie dogs to “infest” their land.
The claim that prairie dogs strip the prairie clean and leave nothing for larger herbivores to eat is also incorrect. In fact, far from avoiding prairie dog towns, bison are attracted to them and, given the chance, will spend a disproportionate amount of time grazing on the rodents’ well-maintained lawns of tender young blue grama and buffalo grass. Although prairie dogs do eat plants that bison, or cattle, might otherwise consume, they compensate, at least in part, by maintaining patches of highly nutritious, highly digestible fodder. Presumably this fact explains why cattle that share the range with prairie dogs may gain weight almost as fast as those that have the pasture to themselves. Although the arithmetic varies from case to case, the monetary reward for removing prairie dogs is often offset by the expense of “controlling” them.
The ecological benefits of sustaining prairie dogs, by contrast, are incalculable. Prairie dogs are the beavers of the grasslands, in the sense that they reengineer the environment and create living space for an astonishing variety of other creatures. Through their constant gnawing, they not only maintain fresh fodder for cattle and bison but also increase the diversity of the vegetation by opening up space for forbs such as scarlet mallow (or globemallow, as it is also called) and prickly pear cactus. These plants, in turn, provide food and shelter for other herbivores, including insects, birds, mice, rabbits, and hares. Some of these animals—cottontails, for example—are also attracted by the shelter of the prairie dogs’ mounds, where they can tuck themselves down out of the sun for hours at a time. Burrowing owls just move right on in, laying claim to abandoned burrows (usually on the outskirts of town) and building their nests underground. In the hazy heat of midsummer, the little owls can sometimes be seen standing, swivel-necked, at their burrow mouths or flapping languidly over the colony in search of grasshoppers.
Black-footed ferret
More than 160 species of vertebrates have been observed on prairie dog colonies. Although some are drawn by the opportunities that prairie dogs create, others are attracted by the prairie dogs themselves. The plump little rodents figure in the diets of a host of predators, including two species of rattlesnakes and a dozen different kinds of hawks, plus weasels, skunks, badgers, bobcats, coyotes, and foxes. Prairie dogs also are, or at least once were, the sustaining resource of what is now one of the rarest carnivores on Earth. The black-footed ferret—a sinuous, mink-sized weasel with a black-bandit mask—is built to slink through prairie dog burrows and capture the rodents when they least expect it. Not surprisingly, as prairie dog populations dwindled, the ferrets also became increasingly rare. To make matters worse, the ferrets are also subject to canine distemper and to plague, an introduced disease that is endemic in prairie dog colonies. Under this malign confluence of influences, the species has come within a heartbeat of extinction. By 1987, only eighteen individuals were known to exist, in a single prairie dog town in Wyoming. Now, all these years later, the descendants of this remnant population are being bred in captivity and reintroduced to selected prairie dog towns across the plains, from Saskatchewan to Mexico. Although their future remains precarious—the threat of disease is always there—the population has grown from essentially zero to around a thousand.
Under the watchful glare of a parent, right, two young burrowing owl chicks venture out of their den.
Arthur Savage photo
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> GOING SQUIRRELY
No fewer than six species of ground squirrels are found on the rangelands of the Great Plains, all members of the genus Spermophilus, or “seed-lovers.” Of these, three can be identified by their handsome spotted coats. The sprightly thirteen-lined ground squirrel—which really does have thirteen stripes, plus an elegant grid of spots—is found across the entire span of the prairies and is the most common species in parts of the Dakotas and Nebraska. The Mexican ground squirrel—which sports nine parallel ranks of squarish spots but no dark stripes—is restricted to Texas, New Mexico, and other points south. Meanwhile, the spotted ground squirrel—which is spangled with dots arranged at random, with neither stripes nor rows—is found on dry, sandy grasslands across the south-central plains, from the Nebraska Sand Hills to southwestern Texas.
The rest of the squirrely crew is outfitted in plain brindled coats. Franklin’s ground squirrel, a.k.a. the gray gopher, is a largish, plume-tailed rodent that is most at home in thick stands of grass or brush. It ranges along the eastern border of the plains, from Kansas north, and then follows the arc of the Aspen Parklands west into Alberta. The other two species are so similar that until quite recently they were thought to be one and the same. The dapper Wyoming ground squirrel is restricted to three isolated pockets in the western United States, two in the mountains and one smack in the middle of the prairies, in the vicinity of Cheyenne, Wyoming. By contrast, its cousin, the Richardson’s ground squirrel, is found across the n
orthern plains, from the Canadian prairies to the central states.
Richardson’s ground squirrels—more familiarly known as “flickertails” or “prairie gophers”—look like nothing so much as miniature prairie dogs. The same quivering alertness. The same bolt-upright stance. The same flying flick of the tail as they scoot underground. The similarity between the two species even extends to the intimate details of their living arrangements. Like female prairie dogs, female gophers live in clusters of close kin, seeking safety in the company of their mothers, daughters, nieces, and aunts. The males live on the margins of the colony—or even all alone—in much the same exposed and vulnerable positions as male prairie dogs.
But there is one striking difference between the two species. Unlike ground squirrels, prairie dogs do not hibernate. Although they become dormant for a few days when the weather is extreme, they soon rouse, return to the surface, and resume eating. Ground squirrels, by contrast, go underground in late summer, curl up in a ball, and lapse into a state of utter torpor. Although their tissues occasionally warm themselves, the animals “chill out” for as long as seven months, often sinking to the temperature of the frozen ground. During this whole period, they do not wake or drink or eat; they just lie there conserving energy. This spectacular ability may explain why gophers—and not prairie dogs—are abundant on the winter-bound Canadian plains and have prime importance in the local ecology.
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Pronghorns: Outwit, Outplay, Outlast
Since the moment when Brewster Higley penned his verses on the banks of Beaver Creek, “discouraging words” about the future of the prairie’s unique plants and animals have been heard all too frequently. In the last quarter century, for example, burrowing owls have essentially disappeared from the Canadian prairies, despite concerted efforts to sustain them, and declines have also been detected in many parts of the American plains. Similarly, the populations of mountain plovers, pale killdeerlike shorebirds that nest right out on the bald-headed prairie, often on prairie dog towns, have plunged by more than 60 percent in the last forty years. Much-loved birds, like prairie chickens, have been declining steadily, and signature species, like burrowing owls, have also been losing ground. “Less” and “fewer” have become our watchwords.
Happily, some species have bucked these dismal trends; the pronghorn is chief among them. Once as fantastically abundant as bison, with an estimated precontact population of 35 million head, the species was decimated by over-hunting during the settlement era. By 1900, the herds had been reduced to a tattered remnant of some 15,000. But a determined conservation effort turned the situation around, and the herds have rebounded several-hundred-fold in the last century. The count currently hovers around 1 million animals.
The pronghorn is a survivor. Although dozens of related species once roamed the Great Plains, only one, Antilocapra americana, made it through the mass extinctions at the end of the Ice Age. In so doing, the pronghorn permanently outdistanced its most fearsome predators, including North American lions and dire wolves; yet even today, it flies across the prairie as if they were still in hot pursuit. The fastest animal in North America, and possibly in the world, it can hit speeds of 60 miles (100 kilometers) an hour and maintain a blistering pace for a couple of miles. Running open mouthed, it gulps air down its extralarge windpipe and into its extralarge lungs, as its powerful heart keeps its muscles fueled with oxygen. This is a species with the prairie in its blood, the animal world’s answer to wide open spaces.
Even the normally stolid Captain Clark—of Lewis and Clark fame—was moved to poetry by the pronghorns’ grace and speed, which put him in mind of “the rapid flight of birds.” Other observers were reminded of gazelles and jumped to the conclusion that pronghorns were a kind of antelope. (In fact, antelope are bovids, like bison and cattle; pronghorns are the only members of their own unique family and genus.)
Naturalists have found the pronghorn’s social life even more deceiving. Although pronghorns of all ages and both sexes congregate during the winter, the herds break up in the spring, as the animals spread out across the prairie. Mature males—the big guys with the forked black horns—often lay claim to one or two sections of rangeland, which they defend against other bucks. Meanwhile, the does—the ones with the straight, short horns or occasionally none at all—gather in small herds that move unhindered from one male territory to another. Or so it goes until late summer when, with the approaching rut, the mature males begin to aggressively herd the does, as they stake sexual claim to their “harems.” At least, this is what early observers thought was going on.
With the hairs on his rump flared in alarm, a pronghorn flashes a warning to the rest of the herd as he darts away from danger.
What actually happens turns out to be far more mischievous. Although the males do their best to keep tabs on the does, they are not always successful. If a female can’t break away from the buck with a feint and a bound, she may outwit him by urinating in front of him. Distracted by her deposit of intoxicating scents, he indulges in flehmen, or intense sexual sniffng, while she makes a run for it. In the weeks just before estrus, a female may visit several breeding males before consenting to mate, apparently basing her decision on the bucks’ relative ability to protect the herd from harassment and their success in male-to-male combat. Sometimes a female sneaks away from the herd just long enough to attract a consort of nonterritorial, or bachelor, males and returns to parade them past the harem buck. Standing safely out of harm’s way, she then watches the snorting, pawing, rushing, and chasing that ensues, before presenting herself to mate with the victor. Far from being complete masters of the situation, male pronghorns are in much the same position as grouse on a lek as they strut their stuff before a discerning audience.
If the hidden quirks of pronghorn society are only beginning to be understood, one aspect of their biology has been clear from the outset. Although pronghorns are native to grasslands, they do not eat very much grass. As a result, they are perfect companions to grass-eating species such as bison and cows and do not interfere with the commercial production of cattle. In lieu of grass, pronghorns prefer a diet of shrubs and forbs, using their small, dainty muzzles to nip off the choicest morsels. This ability to forage selectively, one mouthful at a time, is important because many of the pronghorns’ favorite foods are laced with poison. In the long evolutionary struggle between herb and herbivore, plants have fought back with every weapon at their disposal. Just as grasses contain grit that wears down herbivores’ teeth, so many grassland forbs contain toxins that can cause indigestion, liver damage, miscarriage, and other bodily harm. (Locoweeds, lupines, and larkspurs are just three of a long list of prairie plants that regularly kill cattle.) But through evolution, many prairie herbivores have responded to this threat by developing the ability to neutralize certain of these toxic agents. For example, sage and sagebrush contain turpentinelike compounds that if ingested and left unchecked, interfere with the microorganisms in an ungulate’s complex stomach. Cattle avoid sages, and even mule deer can’t eat too much, but pronghorns have completely mastered the challenge. Sage and sagebrush are among their staple foods and feature in their diet throughout the year.
Prairie sage
Silver sagebrush
Wile E. Coyote and Co.
The first rule of ecology, on the rangelands as everywhere else, is that everything and everyone eventually gets eaten. But because organisms expend so much energy in daily living, only a fraction of what they ingest is converted into living tissue, or biomass. The proportion that is available for transfer to the next trophic level is usually no more than 10 percent. As a result, it takes a vast span of grass to support a herd of herbivores, which in turn can sustain only a handful of predators. Yet despite their relative scarcity, predators are present on the rangelands in every conceivable size and shape, from eight legged to six legged to no legged. Think of spiders, tiger beetles, ladybugs, assassin bugs, robber-flies, and wasps; think snakes, lizards, turtles, f
rogs, toads, owls, and hawks; think shrews, weasels, skunks, and wild cats. Time was when the catalog would also have included wolverines, cougars, grizzlies, American black bears, and wolves, but those species were pushed off the plains during the settlement era. Wolves in particular were targeted for extermination with strychnine, traps, and guns, as an insult to commerce and a threat to civilization. (Today, although young wolves sometimes migrate across the prairies from the mountains and the north woods, they are inevitably shot or hit by a car before they have a chance to settle in.)
In the Bad Guy/Good Guy paradigm of the nineteenth century, the eradication of wolves should have been pure gain. Instead, it merely opened the way for a new breed of “outlaw” predator to move into the vacated space. As long as wolves were the dominant canids on the prairie, their slightly smaller cousins, the coyotes, didn’t stand much of a chance. Any coyote that entered a wolf territory was likely to meet a bloody end, a victim of the cold logic of interspecific competition. As a result, coyotes were generally restricted to the gaps, or buffer zones, between packs of wolves and, though widely distributed across the plains, were nowhere plentiful. At least that is the impression one gets from the accounts of early explorers, who seldom mention seeing coyotes or, to use their phrase, “bush wolves.” By contrast, both red foxes and the diminutive (pussycat-sized) swift foxes appear to have been widespread and common in some localities, perhaps because they were too small to compete with wolves and thus were allowed to go their jaunty way without interference.
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