Neither injured, nor deformed: Why some birds stand on 1 leg

Posted by JEFF KIDD on November 24, 2013 

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.

Sanderlings, semipalmated plovers and other small shorebirds display this hopping behavior often. Larger ones — willets, greater yellow legs and marbled godwits, for example — frequently stand on one leg but don’t hop as often, “for the same reason a 5-year-old child finds it easier to hop than an adult,” Marsh said. “They don’t weigh as much.”

One-legged posture is most prevalent on cold days, but because retaining heat isn’t the only reason birds do this, it can be observed in warm weather, too.

Herons, egrets and birds of prey — with their heavily muscled legs — often stand on leg. Occasionally, songbirds will, too, but because the unfeathered portions of their legs are relatively short, they have less need to do so, Marsh said. When they want to warm up, songbirds are more likely to fluff out their feathers to cover exposed parts.

And seldom will these species hop like shorebirds, Marsh said. In fact, their feet aren’t made to move along the ground much at all.

“Songbirds have feet adapted for perching,” Marsh said. “They have well-pronounced toes, and they’re opposable so that they can use them to grasp around a branch.”

Shorebirds have feet adapted for running — feet with stubby rear, fourth digits that leave three-toed prints in the sand. Turkeys and bobwhites have similarly constructed feet, which aren’t great for perching, Marsh said, but help ruddy turnstones, gulls and other birds you’re likely to see walking on the beach skitter across the sand.

“They do just like we do when we walk or run and land so that the middle part of their foot acts like a heel,” Marsh said. “They use that to push off.”

Note that this fish crow, photographed this weekend at The Sands in Port Royal, has a pronounced rear toe — great for perching but awkward for ambulation.

Birds do occasionally injure their feet and legs and are occasionally born with deformities, Marsh said. However, “injured legs actually droop — just the opposite” of the tucked posture that so often fools bird-watchers.

Still, some take pity. There’s even a a Facebook fan page devoted to birds on one leg (although it had a grand total of 20 fans after I clicked its “like” button.)

So for the unconvinced and inconsolable, there is this discussion at the iBird website about the ability of one-legged or gimp birds to survive. The crow described there seems to be doing just fine, and it really is missing a leg.

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