John M. took this photo at the first dig of the day. The dogs were certain there was a groundhog home, but it was buried deep and had not moved for a few days due to the weather.
At this time of year, the groundhogs will wall themselves in behind a dirt barrier, and their heart rates and body temperature will start to drop from 80 beats a minute a minute, and a body temperature of 98 degrees, to as low as 5 beats a minute and a body temperature of just 38 degrees.
Locating a groundhog underground when they go dormant and have walled themselves off in a side tunnel with as much as a foot of dirt between them and the main pipe, is a very hard task for a dog. I have worked groundhog in the snow, and in December, January and February, so it can be done, but I think when that happens it's often because a groundhog has come out of torpor to go topside to defecate. They will still do that every once in a while, even in deep winter.