A Downy Woodpecker

This cute downy woodpecker, Picoides pubescens,  landed in a tree near me while I was taking a walk earlier this week. He sat in this vertical pose, typical for a woodpecker, just long enough for a quick photo. Click to enlarge. 

Woodpeckers have a few special features that help them sit upright clinging to the sides of trees, and also to climb up, down, and sideways on tree trunks while pecking for insects. First, like most woodpeckers, this downy's feet have two toes that face foreword and two that face back. It's called a zygodactyl foot. And second, he has a few stiffened tail feathers that act like a prop for support. He can sit quite comfortably in an upright position on the side of a tree or vertical branch. Click here for a close up of a downy woodpecker's foot. 

Most perching birds have a different arrangement of toes -- like this robin. Notice how three of his toes face foreword and one faces back. It's called an anisodactyl foot and is the most common kind of bird foot.