Prairie dog and Clark in 1804. Lewis described it in more detail in 1806, calling it the "barking squirrel". On average, these stout-bodied rodents will grow to be between long, including the short tail, and weigh between . Sexual dimorphism in body mass in the prairie dog varies 105 to 136% between the sexes. Among the species, black-tailed prairie dogs tend to be the least sexually dimorphic, and white-tailed prairie dogs tend to be the most sexually dimorphic. Sexual dimorphism peaks during weaning, when the females lose weight and the males start eating more, and is at its lowest when the females
Black-tailed prairie dog for expansion, in Wind Cave National Park, 88% females were pregnant and 81% of young weaned, compared to an old colony (30 years) with no room for expansion, where 90% of females were pregnant and 41% of young were weaned. Black-tailed prairie dog gestation is 34 days. Parturition occurs underground. Information about litter size at time of birth is unavailable, but the mean litter size observed above ground ranges from 3.0 to 4.9 young/litter. Only one litter is produced each year. In captivity, black-tailed prairie dog pups open their eyes at 30 days old. Pups are altricial and remain below