The woodchuck is also commonly known as the groundhog. It is a kind of marmot (as are squirrels, prairie dogs and chipmunks), and marmots are rodents. It is a herbivore.
A woodchuck will generally weigh between 2 and 4 kg (4.5 to 9 lb.), but it can reach a weight of 7 kg (15.5 lb.) in autumn. Its body is usually 40 to 65 cm long (16 to 25 in.). Its fur is usually rusty brown with dark feet, but black, dark brown, blond and even white are not unusual.
Woodchucks are burrowers, and they have strong, claw-tipped paws. They dig extensive tunnel systems that include a main entrance, lookout posts, a latrine chamber and a nesting or sleeping chamber.
The nest is where the only litter of the year is born, and it averages four to five young. Although woodchucks are considered solitary animals, males sometimes stay around for a while after breeding. Also, a breeding pair may hibernate in the same den, as may a mother and her young.
The woodchuck is a true hibernator. The first woodchucks start hibernating in late September, and by the end of October all are underground in their dens. They will not wake up and re-emerge until early spring. While hibernating, the woodchuck's metabolism slows considerably: its body temperature drops from 37°C to 4°C (99°F to 7°F), and its heart rate decreases from 80 to 5 beats per minute. A breath may be taken as infrequently as once every six minutes. During hibernation, they lose 17% to 55% of their weight. Adult males emerge first in spring, followed a few weeks later by the adult females.
When they are outside their burrows, woodchucks appear to be constantly on alert. If they become alarmed, they will let out a shrill warning whistle. Because of this, woodchucks are also known as whistle pigs. They squeal when they are fighting, seriously injured or caught by a predator. They are also capable of producing a sound by grinding their teeth together, as well as a low bark.
Woodchucks occur only in North America. They were once uncommon in woodland clearings, but they have thrived since clear-cutting of forests and western-style agriculture arrived in North America. They are found from Alaska and British Columbia to Labrador and as far south as Louisiana.