As of now, I found two large/old Populus tremula trees on campus with concentrations of flying squirrel scat at the base of the tree. The base of the tree shown on this photo is surrounded by shrubs, which form a kind of cage difficult to access. The flying squirrel probably also thought so, because we found a number of footprints, which I believe to be Pteromys volans footprints, in the snow near the base of the tree. There was no track; it appears the animal made one step, or a few steps, and then went back up the tree.