THREETOES are the hardiest of our Woodpeckers, enduring the northern cold with unconcern and remaining in their favorite haunts when the mercury has sunk into the bulb. They congregate in small companies among dead trees in burned-over tracts but separate into pairs among living trees. I stood at the foot of a spruce on Moosehead Lake, Maine, while one edged down the trunk toward me, chirking his curiosity at every jump. When he was within a foot of my cap I squeaked like a mouse and he slid behind the tree but peeked with almost snakelike head-projections.