"Black-tailed prairie dogs exhibit the most complex social behavior of all prairie dogs. Social groups called ""coteries"" live together in very large colonies called ""towns."" The largest town ever recorded stretched for 65,000 square km (25,000 square miles) under Texas prairie. An estimated 400 million prairie dogs lived there. Topographical or vegetational features serve to subdivide the towns into clusters of coteries. The members of each coterie cooperate to defend their territory against others. Black-tailed prairie dogs are active all year, although they may spend extended periods of time underground in winter. They breed in February or March and usually have 3 or 4 young, who are first seen aboveground in May or June."

Links:
Mammal Species of the World
Click here for The American Society of Mammalogists species account