=THE PRAIRIE-DOG= (=Cynomys ludovicianus= and its relatives) (_For illustration, see page 538_) Prairie-dogs are not “dogs,” but typical rodents, first cousins to the ground squirrels, or spermophiles. As a rule, they may be distinguished from the ground squirrels by their 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 five 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, having 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. Southward 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 mountainous parts of Colorado and Arizona. Owing to their diurnal habits, their exceeding abundance over vast areas, and their interesting 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 number 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 illustrated 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.