Nuthatches cling to the bark and can move in any direction. They do not use their tail for a brace when climbing - just their two feet. The hind toe is particularly important for clinging and it's relatively large and strong. Usually they position one foot above the other so that the lower foot acts as a brace while the upper foot clings to the bark. This is a Red-Breasted Nuthatch working the tree for little caterpillars.
