Guide

Happening unseenMammals

How woodchucks hibernate underground

November to January

Woodchucks are hibernating in grass-lined chambers below the frost line, the entrance sealed off with dirt. Their body temperature falls to a few degrees above the burrow's and their heart slows to a few beats a minute.

Why this time of year

Most woodchucks are denned up by the end of October, so from November on the burrow mouths along hedges, wood edges and stone walls are quiet and the animals are deep asleep until late winter.

How to notice it

  1. Walk a hedgerow, stone wall or wood edge by day and look for a bare hole about 5 to 6 inches across, the size of a woodchuck burrow entrance. An open hole like that may be a summer burrow: the winter den is often in a wooded area, with its entrance sealed off with dirt.
  2. Stay a few steps back and look for what is missing: no fresh tracks, no new dirt, no one sitting at the door. Somewhere nearby a woodchuck is below the frost line in a chamber sealed with soil.
  3. Picture the sleeper: curled in a nest of dried grass and leaves, body temperature close to the burrow's, heart slowed to a few beats a minute. Every so often it warms up and wakes for a spell, then goes back under.

Try this with kids: Find a hole and guess how deep the sleeper is. The nest is below the frost line, so how many ruler-lengths down might that be?

Phrase to know: The “frost line” is the depth the ground freezes to in winter.

Safety

  • Look from a distance and do not poke, dig at or block any burrow hole; holes can also trip walkers.

Sources

  • northernwoodlands.orgLi Shen, Northern Woodlands: woodchuck enters hibernation in October curled on a bed of grass; body temperature drops to a few degrees above burrow temperature; heart rate to about three beats a minute; periodic awakening every ten days or so.
  • northernwoodlands.orgSusan C. Morse, Northern Woodlands: entrances 5 to 6.5 inches in diameter; males interrupt hibernation in late winter to search for female burrows.
  • portal.ct.govConnecticut DEEP fact sheet: most woodchucks begin winter sleep by end of October, curled in nests of dried grass and leaves in burrows below the frost line; burrow entrance sealed off with dirt. Woodchucks may have 2 burrows: a winter den in a wooded area and a summer den in open areas; burrows 2 to 5 feet deep.
  • esf.eduSUNY ESF: winter spent curled in a nest in an earthen chamber plugged with soil; heart rate declines to 4 or 5 beats per minute from 80-100.
  • pa.govPennsylvania Game Commission: denning begins with the hard frosts of October, few active past November 1; body temperature into the low 40s F; heart slows to four beats a minute; males emerge before females in February and March.

Checked against these sources on October 2, 2026.

In the guide for November, December, January

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