The black-tailed prairie dog (Cynomys ludovicianus) is the Texas representative of five species of stout, short-legged, short-tailed terrestrial squirrels that occur in the western states of North America. The name prairie dog derives from the barks or yipping calls of this sociable, diurnal rodent whose yellow-grey or buffy appearance and noisy, active presence relieved the monotony of traveling over the short-grass plains in the nineteenth century. Adult prairie dogs weigh two to three pounds (1–2kg) and become sexually mature in their second year. They produce one litter with an average of four or five young in the spring or summer. The young first appear above ground at about six weeks of age. Prairie dogs eat low-growing grasses, weeds, some prickly pear, and, occasionally, animal matter, mainly worms.
In August 1841 George Wilkins Kendall came upon a "commonwealth" of prairie dogs whose "mercurial and excitable denizens" provided some sustenance for the famished and disoriented members of the Texan Santa Fe expedition, which had started north of Austin two months earlier. He admired the "wild, frolicsome, madcap set of fellows...ever on the move...chattering away the time, and visiting from hole to hole to gossip and talk over each others affairs." Kendall was referring to the socially integrated activities of these animals, which include mutual nuzzling, grooming, and "barking" to express territorial claims. Prairie dogs occupy colonies called "towns," often 100 hectares (247 acres) in area or more, which may be divided into "wards" by physical features such as ridges and gullies, and further subdivided into "coteries," or family groups, averaging about eight individuals. In nineteenth-century Texas some of these towns extended over an enormous area. James Frank Dobie summarized several accounts of prairie dogs by noting that in 1852 a single town of some fifty million animals occupied a million acres of the Llano Estacado. In 1853 another dog town along Brady Creek, a tributary of the San Saba River, contained an estimated thirty million prairie dogs in a fifty-mile-long, ten-mile-wide area. Dobie also noted that as recently as 1900 a dog town extended 250 miles north from San Angelo to Clarendon and was 100 miles wide, having an estimated 400 million animals. In 1905 biologist Vernon Bailey calculated that the Texas population was 800 million prairie dogs in an area of 90,000 square miles (233,100 square kilometers), "from Henrietta, Fort Belknap, Baird, and Mason west almost to the Rio Grande, north over the Staked Plains and the Pan Handle region, and south to the head draws of Devils River, to ten miles south of Marathon and twenty-five miles south of Marfa."
The typical prairie dog hole descends vertically from a small, volcano-like dirt cone on the ground surface into a number of passages of varying lengths, which may descend three to five meters below ground. The prairie dog carefully tends the dirt pile built up on the surface in order to prevent water from flooding its burrow system, and uses grass to line the nesting cavity in which the young are born. In severe cold the animals become dormant. They feed on grasses and herbs surrounding their burrows, and are subject to predation from hawks, coyotes, skunks, foxes, rattlesnakes, and badgers. They also are a favorite target of "varmint" hunters.
Researchers suggest that prairie dog numbers increased in Texas during the latter part of the 1800s as stockmen reduced their natural predators and killed off bison and pronghorn antelope which competed for forage. Some experts have also argued that grazing by domestic livestock helped to keep vegetation low, thereby assisting with prairie dog survival. Ranchers and farmers, however, began a war on pasture-feeding prairie dogs, which intensified after about 1914 when Donald A. Gilchrist directed rodent control in the Texas district for the United States Department of Agriculture's Bureau of Biological Survey. The federal government joined forces with county agents and landowners in order to poison prairie dog towns. An effective formula, including strychnine, cyanide, and syrup on a corn or wheat base, was pioneered in 1901. It was used in a modified form in Texas with 200,000 pounds of poisoned grain annually; as a result, dog towns disappeared quickly. In 1918 Vernon Bailey noted dramatic declines around the San Angelo region, where only about a dozen colonies remained. "Not ten percent of the prairie dogs here a few years ago are now alive," he concluded. Twenty years previously they had been "swarming." Control operations persisted, and sizable inroads into West Texas prairie dog numbers occurred in the 1920s. In the mid-1970s, a survey of aerial photographs turned up 1,336 prairie dog colonies extending over 36,432 hectares (89,987 acres) in eighty-nine counties. The black-tailed species continues to inhabit the same ancestral range in the western third of Texas, but habitat loss through the expansion of cropland and metropolitan areas, plus poisoning, has served to reduce the state population to an estimated 2.2 million animals.
The results of attempts at elimination or control of prairie dogs have been both good and bad. Though the animals definitely compete with livestock for forage, some scholars believe that the expansion of brush brought about by the reduction of prairie dogs has caused greater losses of livestock forage than the animals themselves. The poisoned grain and fumigants used to kill prairie dogs also kill other species that inhabit prairie dog towns or eat prairie dogs. Species so affected include the burrowing owl, some hawks, the cottontail rabbit, various reptiles, and, at one time, the black-footed ferret.