Early fall, September and October, is when woodchucks are ready for hibernation. One woodchuck per burrow or in some cases two young ones going into their second year. They climb into their den and seal it off with dirt to keep in the heat. They curl into a ball, resting on their hind legs with nose tucked between them. The tail curls forward and eyes are tightly closed.
Breathing slows until it has almost stopped.
They take 14 breaths of air per minute compared to the normal of 262. While hibernating, they live off of the stored fat on their bodies. Those who did not put on enough fat emerge from hibernation as early as February. Those who remain in hibernation until late March or April lose as much as half of their bodies weight. When they emerge in the spring, they are ready to search for a mate and start the breeding season.