Birds’ feet do more than grip a branch or paddle around

The adult bald eagle dropped to eye height and cruised across the rocky point, made a remarkable U-turn and immediately plunged its legs into the water, rising quickly with a small fish.

No hesitation. Accurate. No checkout lines. No food shipped from a country far, far away. Catch prey. Find perch. Rip and tear. Satisfaction.

Now there’s a relationship with food.

And there’s a set of toes worthy of admiration. An eagle’s foot has four toes, three pointed forward, one back. At the tip of each toe is a talon, made of the same material as our fingernails, but with razor-sharp points.

The surface of eagles toes are rough, and that in addition to the powerful grasp helps the eagle keep its grip on a slippery fish.

Bird feet, like their bills, offer clues to the environmental niche that each species holds, although that’s not the case 100 percent of the time. (A semipalmated sandpiper has slightly webbed feet, but it doesn’t swim.)

Eagles need strong toes and claws with ripping ability. In general, toes for perching, food catching, manipulating food and climbing have sharp curved claws, even though the size of the bird varies greatly.

Feet are used for the obvious (hopping, killing, swimming, carrying) and the not-so-obvious (aerial courtship, preening, egg-cradling) reasons, including absorbing the impact of hitting water.

Runners and scratchers have strong feet with blunt claws (grouse); swimmers generally have webbed (ducks) or lobed (coots) feet. Nuthatches’ claws are more curved than nonclimbers as an aid to grasping bark.

Most birds (and nearly all perching birds) have four toes, usually three forward and one back (think big toe), but woodpeckers have a two-and-two arrangement. Owls have one toe with a flexible joint that allows the toe to be moved into either position.

Tendons that extend from muscles control the toes. Extend the leg to full length, the toes open as the leg extends. Think of the eagle coming in for the kill, legs extended, claws wide open. When the leg is flexed back toward the body, the toes close and grasp.

This leads us to an answer to that burning question: Why don’t sleeping birds fall off their perch?

When a bird hunkers down on the perch to sleep, it’s flexing its legs back toward the body, and the automatic response is for the toes to grip the perch and stay locked until the bird awakens and straightens its legs.

One bird whose toes don’t grasp anything is the ostrich. It has two very large toes more reminiscent of a horse than a bird, both pointed forward. It can escape danger by running up to 30 mph on those toes, very useful for a bird that cannot fly.

Birds actually move on their toes because the heels are off the ground because of the way the foot is structured.

It’s an illusion that birds’ knees bend backward. Those joints are actually their ankles, and the knees are usually hidden near the body.

Birds’ legs are generally bare, but those with feathers might use them for insulation (ptarmigans) or to muffle flight sounds (owls). The feet are unlikely to freeze because there’s very little muscle, so there aren’t many nerves and blood vessels to affect. Hawks and owls have more muscles in their feet, and have more feathers for insulation.

Some birds have a little extra on their toes. A barn owl has a weblike piece that’s used for grooming; a great blue heron has a serrated edge on the side of its middle claw (three of four toes are pointed forward) that’s used for preening.

Birds don’t have hands (their forelimbs are devoted to flying) but they do have remarkably effective designs.

Columnist Sharon Wootton can be reached at 360-468-3964 or www.songandword.com.