Raking the garden beds today, I noticed that the ones that had been underneath the piles of snow I'd blown from the driveway had many little rodent nests and burrows in them.
When I used to have the driveway plowed, the snow was all pushed along the driveway, creating an artificial glacier beside the garage. Nothing lived in that. It was very dense and tightly packed.
Even in previous years since I've been clearing the driveway with the snowblower I had not noticed this much nesting activity -- possibly because I was not the one clearing the garden beds. But I think the combination of deep cold and powdery snow created a need for nesting shelter and an ability to create it in the snow piles I made.
They might also have been driven to camp out because I used the garage more and had treated it with a lot of peppermint oil in the fall to discourage occupancy. And the rate at which I used firewood in this deeply cold winter meant that they couldn't hang out in the wood pile for long.