Liesl thought it was a black squirrel. But as soon as I saw it, I knew it was too big and too weaselly. My thoughts kept saying "pine marten or something..." until I realized that it was in a pine forest and that was probably what it was. We lost track of it as it jumped from tree to tree. But as we went around the corner, it ran across the road in front of us. We were able to watch it for a few more moments as it climbed about 10-12 feet up a pine tree and then leaped down to the snow below--clearly playing--and eventually it was out of sight. On the way home, we stopped in at the library. An animal almanac was on display. I opened it and turned right to the page with a picture of a pine marten.
nunemaj
Follow-up... A friend who lives in that neighborhood says that he has regularly seen a pine marten hunting squirrels. I wonder if it is the same one?