Black-tailed prairie dogs live in complex colonies, or towns, of burrows and tunnels. While original colonies covered many square miles of territory, today prairie dog colonies are smaller and more isolated. Each town is divided into territories, with each territory divided into a "coterie". A coterie refers to the area inhabited by a family unit, which usually consists of one male, one to four females, and their offspring. Prairie dog colonies can contain several hundred individuals.
Within the coterie, separate underground rooms are dedicated to sleeping, storing food and rearing young. Burrows are marked by mounds of packed dirt that serve as a lookout and protect the burrow from floods. The burrowing process improves the soil, mixing organic material from above, and providing a nutrient rich environment for plants and animals living around the prairie dog ecosystem. Burrows can be as much as 10 feet deep.
Colonies are generally located in dry grassland. Prairie dogs are primarily herbivores, feeding on grass and other prairie plants. Varieties include western wheatgrass, buffalograss, scarlet globemellow, rabbitbrush, prickly pear cactus and thistle. In the winter, prairie dogs will eat more root matter due to the relative lack of forage above ground. At times, they will also eat insects such as grasshoppers, beetles and cutworms. As the dominant animal in the landscape, prairie dog foraging patterns help define the types and diversity of grasses present in and around colonies.
Prairie dogs are known as a keystone species due to the number of other species that depend on them. Many predators rely heavily on the prairie dog, such as the black-footed ferret, peregrine falcon, coyote, bobcat, various types of bear and red fox. Due to the size and nature of their colonies, prairie dogs provide entire ecosystems that attract particular types of insects, which in turn attract particular bird species, such as the horned lark, mourning dove, mountain plover and long-billed curlew. The black-footed ferret and the burrowing owl rely on the prairie dog for shelter as well, residing within the burrows and tunnels.