Woodchucks are primarily active during daylight hours. When not feeding, the sometimes bask in the sun during the warmest periods of the day. They have been observed dozing on fence posts, stone walls, large rocks, and fallen logs close to the burrow entrance. Woodchucks are good climbers and sometimes are seen in lower tree branches.
Woodchucks are among the few mammals that enter true hibernation. Hibernation generally starts in late fall, near the end of October or early November, but varies with latitude. It continues until late February and March. In northern latitudes, torpor can start earlier and end later. Males usually come out of hibernation before females and subadults.
Males may travel long distances, and occasionally at night, in search of a mate. Woodchucks breed in March and April. A single litter of 2 to 6 (usually 4) young is produced each season after a gestation period of 32 days. The young are born blind and hairless. They are weaned by late June or early July, and soon after strike out on their own. They frequently occupy abandoned dens or burrows. The numerous new burrows that appear during late summer are generally dug by older woodchucks. The lifespan of a woodchuck is about 3 to 6 years.
Woodchucks usually range only 50 to 150 feet (15 to 30 m) from their den during the daytime. This distance may vary, however, during the mating season or based on the availability of food. Woodchucks maintain sanitary den sites and burrow systems, replacing nesting materials frequently. A burrow and den system is often used for several seasons. The tunnel system is irregular and may be extensive in size. Burrows may be as deep as 5 feet (1.5 m) and range from 8 to 66 feet (2.4 to 19.8 m) in total length. Old burrows not in use by woodchucks provide cover for rabbits, weasels, and other wildlife.
When startled, a woodchuck may emit a shrill whistle or alarm, preceded by a low, abrupt “phew”. This is followed by a low, rapid warble that sounds like “tchuck, tchuck”. The call is usually made when the animal is startled at the entrance of the burrow. The primary predators of woodchucks include hawks, owls, foxes, coyotes, bobcats, weasels, dogs, and humans. Many woodchucks are killed on roads by automobiles.