Yes, groundhogs hibernate, and they do it properly. A lot of animals slow down in winter, but a groundhog basically shuts itself off for months. That Groundhog Day business in February is a nice story, but the actual animal is usually still asleep in its burrow when the cameras show up.
Here is what I have learned about how groundhog hibernation works, when it starts and ends, and what it means for anyone dealing with one in the yard.
What hibernation actually looks like for a groundhog
A groundhog in deep hibernation is barely alive by normal standards. Its body temperature drops until it is only a little warmer than the dirt around it. Its heart slows to a handful of beats a minute. Its breathing slows to about one breath every few minutes. It runs on stored body fat for the whole winter, which is why a groundhog that did not fatten up enough in the fall does not make it to spring.
It is not one continuous nap either. Every week or so the animal warms itself partway back up for a few hours, then drops back down. Nobody fully understands why it burns the energy to do this, but it seems to matter for staying healthy through a long winter.
When they go down and when they wake up
Groundhogs go into hibernation in the fall, usually around October, though the timing shifts with how far north you are. Colder places mean earlier bedtimes. In the southern part of their range they may not settle in until November, and they wake up earlier too.
They spend late summer and early fall eating as much as they can to pack on fat. That fat is the whole fuel supply for the winter.
Males wake up first in late winter or early spring, a week or two before the females. They are out looking for food and setting up territory. By the time Punxsutawney Phil makes his February appearance, the real groundhogs in most places are still underground.
The winter burrow
Groundhogs keep two kinds of burrows. The summer burrow is for daily life. The winter burrow is dug deeper, below the frost line so the soil around it never freezes, and the groundhog plugs the entrance with dirt from the inside. That plug seals in warmth and keeps out cold air and predators. It also means a plugged hole in the middle of winter is a sign something is still down there.
What this means for controlling them
If you have a groundhog problem, timing matters. Spring through fall is when they are active, eating, and doing damage, so that is the window for trapping and exclusion. In winter they are not causing trouble, but the burrows are still in your yard.
Winter is actually a good time to find and map burrows without the animal running around. Just do not seal one up until you are sure nothing is hibernating inside. Sealing a sleeping groundhog in means it starves.
A quick note on naming: a groundhog and a woodchuck are the same animal. Some folks also call them whistle pigs, because of the high warning whistle they make. If you see a chunky brown rodent out and about in January, it is probably not a groundhog, a true hibernator in deep winter would still be down.
Frequently Asked Questions
They hibernate for most of it, with short wake-ups every week or so where they warm back up for a few hours. They do not come out of the burrow until late winter or early spring.
They live off the fat they packed on in late summer and fall. Their metabolism drops so low during hibernation that they can stretch that fat across the whole winter, and they come out noticeably thinner than they went in.
Yes. An unusually warm stretch or a disturbed burrow can rouse one early. That is risky for them, because there is not much to eat yet. An early wake-up is one of the main ways groundhogs die over winter.
The groundhog plugs the winter burrow entrance with dirt from the inside. The burrow is dug below the frost line, and the chamber is lined with grass and leaves for insulation.
Yes. They are two names for the same animal. Woodchuck is the older name, and it has nothing to do with chucking wood.
