The Third Support on a Tree Trunk

A downy woodpecker lands on the side of a maple tree. Instead of sitting on a branch, it faces upward on the nearly vertical trunk. There is no flat shelf beneath its feet. Gravity pulls it downward, yet it can pause and search the bark for insects. How does it stay in place without flapping its wings?

Under the heading “Three Supports,” imagine a close view of the bird. Its two feet grip rough bark with curved claws. On each foot, two toes point forward and two point backward. Below the feet, the tail presses against the trunk. Together, the feet and tail help keep the bird's body steady. The tail acts as a brace, a support that holds something in place.

A feather has a central shaft, the long part from which its smaller branches spread. In a downy woodpecker's tail, these shafts are stiff and strong, especially in the middle feathers. The feathers can bend a little, but they resist folding under the bird's weight. Their pointed tips meet the bark. A soft, floppy tail would not provide the same firm support.

Climbing is not a matter of leaving the tail fixed in one spot. As the woodpecker moves upward in short hops, its feet take new holds and its tail changes position. After a hop, the bird presses its tail against the bark again. With its body supported, it can pause to inspect a crack or tap with its beak.

Picture a side-view drawing of the resting bird. The caption beneath it reads, “Two gripping feet and a tail pressed against the bark.” The drawing shows the tail touching the trunk below the feet, rather than sticking straight out behind the bird. That lower contact is an important clue: the tail is helping support the body, not simply trailing behind it.

The feet and tail do different jobs. The claws catch on the rough surface, while the tail pushes against it. The tail does not hook into the bark like a claw, and it does not pull the bird up the tree. Instead, its stiff feathers provide an extra place for the body to rest against the trunk.

Watching the beak might tell you where the woodpecker is searching for food. Watching the tail helps explain how it can search while perched upright. The bird's climbing equipment includes more than its feet. A set of specially built feathers turns its tail into a useful third support.