November 25, 2013

Not injured or deformed: Why birds stand on one leg

Some birds merely perch on one leg — a behavior that is quite common among shorebirds and birds with long or thick legs.

The tender-hearted bird-watchers call John Albert most often. The ones who cannot stand to see one of God’s creatures suffer. The ones who take pity on the malformed and mutant.

Oh, those poor one-legged birds!

“I get calls all the time from people who want to report an injured bird and wonder what they should do,” said Albert, Harbor Island’s unofficial resident wildlife expert and Fripp Audubon Club member.

Relax, Albert tells the despondent. That little sandpiper you saw on the beach wasn’t deformed, or even acting deviantly.

This sort of behavior can fool the best of them, though.

One regular Untamed Lowcountry reader, who has observed thousands of birds in her lifetime, recently was departing Pinckney Island National Wildlife Refuge when she noticed a tri-colored heron that appeared to have a deformed foot protruding from its belly. She stopped to take a photo, emailed it around and asked if anyone had seen such a handicap before.

But the bird was merely perching on one leg — a behavior that is quite common among shorebirds and birds with long or thick legs, like tri-colored herons, according to Chris Marsh, an ornithologist and executive director of the LowCountry Institute.

“The thing people have to realize is that people do same thing — we just don’t notice it,” Marsh said. “If people stand in one place for a long time, they tend to shift their weight and stand on one leg. If birds are standing on one place for a long time, the biomechancis are such that standing on one leg is simpler to do.

“So they stand on one leg, too.”

This posture helps birds conserve both heat and energy. According to the website

Birds’ legs have an adaptation called “rete mirabile” that minimizes heat loss. The arteries that transport warm blood into the legs lie in contact with the veins that return colder blood to the bird’s heart. The arteries warm the veins. By standing on one leg, a bird reduces by half the amount of heat lost through unfeathered limbs.

What’s more, standing on one leg is more biomechanically efficient for many species — it places a foot directly underneath their center of gravity, according to Marsh.

“That way, there’s no lateral movement or lateral forces,” so it’s easier to balance, he said.

In fact, the position is so darn comfortable, many species hop on one leg for quite a distance rather than untucking the other leg, as the video below demonstrates.

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