Gregariousness is a common trait of many plains animals. In a land where movement is necessary and concealment difficult to achieve, it provides a definite survival advantage. Bison calves find protection in the herd, where their defense is the concern of all adults. Pronghorns take turns as sentries, allowing the other members of the group to rest and feed. Coyotes are more effective when hunting in pairs. The success of the wolf in bringing down large prey and even evicting grizzlies from their kills was largely due to their family group or pack organization. But lacking physical adaptations for speed and mobility, prairie dogs are forced to rely on their burrows for refuge. The need to remain close to their burrows imposes on the animals a serious problem: how to maintain an adequate food supply? Although a dog town might appear to be one big collection of affectionate family members, all coming and going at will, the impression is false. Instead, each town is divided up into small groups of related animals. These family groups, called coteries, are the basic social unit, much as human families are in our own society. As the prairie dog pups soon learn, each coterie defends its own territory from intrusion by others, thus preserving for itself necessary living space and an adequate food supply close to the safety of its own burrows. Only in times of dire emergency, when the scramble to safety supersedes all territorial claims, will prairie dogs allow other coterie members the use of their burrows. So strong is an offending animal’s sense of trespass, it will often brave the hazard of dashing back to its own burrow rather than staying long in a neighbor’s territory. The typical coterie consists of about seven to eight animals, arranged in a hierarchical order. Each usually has a dominant male that protects the coterie’s territory from invasion by other males and oversees the activities of the females and young. If the coterie is a large one, more than one individual may enjoy dominant status and share the duties of leadership. In some cases, females may be dominant in rank; the role generally falls to the males, however, possibly because of their slightly larger size or because they have more time to observe and patrol, not being tied to the demands of the young. Not only their social organization, but also their social behavior makes prairie dogs unique among rodents. The function of coterie hierarchy is cooperative, rather than oppressive, resulting in a remarkable absence of conflict and social stress. Aggressiveness is generally limited to inter-coterie contacts along the invisible boundaries. In an established town, infractions are usually accidental and seldom precipitate lasting disputes. The end result of intra-coterie cooperation and inter-coterie respect is a stable and harmonious town. Energies and attention that would otherwise be squandered in conflict can thus be focused on mutual defense.