SMALLER MAMMALS OF NORTH AMERICA 



435 



larger size, proportionately shorter and heavier 

 bodies, and shorter tails. In length they vary 

 from fourteen to over seventeen inches, and in 

 weight from one and one-half to more than 

 three pounds. 



These rodents are limited to the interior of 

 North America and form a small group of live 

 species and several geographic races. Although 

 closely alike in general form and habits, the 

 species are divided into two sets : one, the 

 most widely distributed and best known, hav- 

 ing the tails tipped with black, and the other 

 having the tails tipped with white. 



On the treeless western plains and valleys 

 from North Dakota and Montana to Texas 

 and thence west across the Rocky Mountains 

 to Utah and Arizona, they are one of the most 

 numerous and characteristic animals. _ South- 

 ward they range into northwestern Chihuahua 

 and one species occupies an isolated area on 

 the Mexican table-land in southern Coahuila 

 and northern San Luis Potosi, Mexico. Their 

 vertical range varies from about 2,000 feet on 

 the plains to above 10,000 feet in the moun- 

 tainous parts of Colorado and Arizona. 



Owing to their diurnal habits, their exceed- 

 ing abundance over vast areas, and their in- 

 teresting mode of living in colonies, prairie-dogs 

 have always attracted the attention of travelers 

 and have become one of the most widely known 

 of our smaller mammals. All who have lived 

 in the West, or who have merely traversed the 

 Great Plains on the transcontinental railroads, 

 have had their interest excited by these plump 

 little animals sitting bolt upright by the mounds 

 which mark the entrances to their burrows, or 

 scampering panicstricken for shelter as the 

 train roars through their "towns." 



So strong is the gregarious instinct in prairie- 

 dogs that they customarily make their burrows 

 within short distances of each other, varying 

 from a few yards to a few rods apart. The 

 inhabitants of these communities, or "towns," 

 as they have often been termed, vary in num- 

 ber from a few individuals to millions. In 

 western Texas one continuous colony is about 

 250 miles long and 100 miles wide. In the 

 entire State of Texas 90,000 square miles are 

 occupied by prairie-dogs, and the number of 

 these animals within this area runs into the 

 hundreds of millions. The extent to which 

 they occupy parts of their territory is well il- 

 lustrated by one situation in a mountain valley, 

 •containing about a square mile, in eastern 

 Arizona, which by actual count contained 7,200 

 of their burrows. 



The burrows, from four to five inches in 

 diameter, are usually located on flat or gently 

 sloping ground. They descend abruptly from 

 eight to sixteen feet, then turn at a sharp 

 angle and extend ten to twenty-five feet in a 

 horizontal or slightly upward course. The 

 tunnel at the end of the steep descending 

 shaft is always more or less irregular in 

 course, and branches in various directions, the 

 branches often ending in a rounded nest or 

 storage chamber, but sometimes forming a loop 

 back to the main passageway. Not infre- 



quently two entrances some distance apart lead 

 to these deep workings. A little niche is in- 

 geniously dug on one side of the steep entrance 

 shaft, four to six feet below the surface, to 

 which on the approach of danger the owner 

 retires to listen and determine whether it may 

 or may not be necessary to seek safety in the 

 depth of the den. It is from these vantage 

 points that the resentful voices of the habitants 

 come to an intruder in a prairie-dog "town" 

 as he passes. 



The black-tailed prairie-dog, which is so 

 numerous on the Great Plains, surrounds the 

 entrance to its burrow with a crater-shaped 

 pyramid of soil varying from a few inches to 

 nearly two feet in height and serving perfectly 

 as a dike to keep out the water. The owners 

 keep the funnel-shaped inner slopes of the 

 rims about the entrances in good condition by 

 setting briskly to work to reshape them at the 

 end of a rain-storm, digging and pushing the 

 earth in place with their feet and molding it 

 into a more compact mass by pressing it in with 

 their blunt noses. 



The white-tailed prairie-dogs pile the dirt 

 from their excavations out on one side of the 

 entrance, as in the case of most other burrow- 

 ing animals. Sometimes the dirt in these piles 

 amounts to from ten to twenty bushels, thus 

 indicating extended underground workings. 



The vivacity and hearty enjoyment of life by 

 the occupants of a prairie-dog "town" is most 

 entertaining to an observer. With the first 

 peep of the sun above the horizon they are 

 out on the mounds at the entrances of their 

 burrows, first sitting erect on their hind feet 

 and looking sharply about for any prowling 

 enemy. If all is well they begin to run about 

 from one hole to another, as though to pass the 

 compliments of the day, and scatter through 

 the adjacent grassy feeding ground. 



The favorite food of prairie-dogs consists of 

 the stems and roots of gramma grass and 

 other richly nutritious forage plants. In addi- 

 ction they eat any native fruits, such as that 

 of the pear-leaved cactus (Opuntia) and are 

 extremely destructive to grain, alfalfa, and 

 other cultivated crops. In addition to ordinary 

 vegetation, they eat grasshoppers and are fond 

 of flesh, sometimes being caught far from their 

 homes in traps set for carnivores. They keep 

 the grass and other vegetation cut down or 

 entirely dug out over much of the "town" and 

 especially in a circle about each entrance 

 mound, apparently for the purpose of obtain- 

 ing a clear view as a safeguard against the ap- 

 proach of any of their many four-footed ene- 

 mies. This habit is exceedingly injurious to 

 the cattle ranges and often results in much 

 erosion of the fertile surface soil. 



The vast numbers of prairie-dogs over so 

 large a part of the grazing areas of the West 

 take a heavy toll from the forage and other 

 crops. As a consequence a campaign of de- 

 struction is being waged against them as the 

 country becomes more and more settled, and 

 they will eventually disappear from much of 

 their present range. However detrimental they 



