Why do some birds spend so much time standing on one leg?

Brainerd – Last week a friend and I were looking at some of my images of waterfowl. I had taken the images earlier this spring on a sunny, warm morning from a blind I had placed on shoreline of wetland.

"That duck [a male blue-winged teal] has only one leg," my friend said. "What do suppose happened to its right leg?"

"If you look closely," I replied, "you'll see its right leg is actually tucked up into its feathers. You can just barely see its foot and toe nails."

"Why is the duck doing that?"

It was a good question.

The behavior is commonplace, often times on frigid winter days when it's obvious the bird is attempting to keep its foot warm. Observe the bird for a few minutes and you'll likely notice it often alternates from one leg to another. Usually the bird also has its feathers fluffed to increase insulation, just as we would add an additional layer of clothing for warmth.

In addition, on those icy days, birds often hunker down on a limb, which places the legs and feet into the relative warmth of the feathers.

Why did the teal do this in balmy weather? The bird didn't need to keep the foot warm.

Some research was necessary, and what I found was interesting.

I often spend hours just standing as a wildlife photographer. Somewhere, years ago, I read that when humans stand for a lengthy time, it is advantageous to shift our weight from foot to another to conserve energy. But, of course, our other foot must retain contact with the ground to maintain our balance.

Take a moment to stand on just one leg and you'll quickly discover you'll expend energy — from your ankles all the way up to your buttocks — to keep balance. It's much more energy-efficient to have both feet on the ground.

Physiologists recently employed a device that can measure off-balance sway, or muscular adjustments to maintain stability. The apparatus resembles a glorified bathroom scale, but of course it's much more complicated. Researchers use the device to study flamingos, a bird that commonly stands on one leg. The study results suggested that during a one-legged rest, the flamingos didn't rely at all on their muscles to maintain balance.

What is unanswered is why some species of birds go one-legged more than others. I've noticed blue-winged teal perch on one leg far more than other ducks. Why, I don't know. One guess: In nature, energy conservation in any form can and often is a big factor in survival.

While on the subject of birds' feet, have you ever wondered why they don't freeze during winter?

Basically, birds' feet don't freeze because of a unique circulatory system. Arteries carry warm blood to the foot, but as the blood returns to the heart via veins, those veins are interwoven with the arteries. The blood is kept warm, or relatively so, owing to contact with the arteries during the return to the heart.

Again, fascinating.