Ron LeValley recently photographed a Pygmy Nuthatch characteristically moving head-first down the trunk of a Pine tree.
Ron says, "Creepers go up the trees and Nuthatches go down!" I asked him what the Nuthatch does when it reaches the bottom. Ron replied, "It flies up to the top and heads down again." They are, of course, looking for insects and seeds on the tree.
Their call is quite distinctive and you can hear it on the Cornell Lab of Ornithology website at this link: http://www.allaboutbirds.org/guide/Pygmy_Nuthatch/sounds
Thanks to Ron for allowing me to share his photo with you here. To see much more of Ron's wonderful photography, here is his website: http://www.levalleyphoto.com/home/