CNN.com - Nature - Why penguins waddle


An Antarctic penguin waddles as he walks

By Don Knapp
CNN Correspondent

SAN FRANCISCO, California (CNN) -- Penguins may do some things with grace and ease, but that funny waddling walk of theirs isn't one of them.

Still, it appears nature gave penguins their waddle for good reason: To conserve energy.

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CNN's Don Knapp reports on the bird's side-to-side gait

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Researchers have known the Antarctic birds used lots of calories when they walked about -- about double the calories of other animals of the same weight walking the same distance.

And researchers assumed it was the waddle that was using up the energy. But a group of University of California, Berkeley, scientists studying five selected Emperor penguins at San Diego's Sea World made a surprising discovery: Waddling appears to help penguins conserve the kinetic energy they generate with calories when they walk.

Researcher Tim Griffin said, "We found that waddling didn't actually require increased work. Instead, walking is costly for penguins because they have such short limbs, which requires their legs to generate muscular force very rapidly."

Think of a bowling pin

So why is the waddle efficient? Griffin calls it the "inverted pendulum" effect, and he compares it to a wobbling bowling pin. Kinetic energy and gravity combine to keep it rocking back and forth over its center of gravity.


An Antarctic penguin waddles as he walks along the snow

Griffin demonstrates with his own legs, showing how his center of gravity rides up and over the leg.

"So when the penguin takes a step, its center of mass is low, so when he stops coming up over his leg, the mass moves to the side," Griffin says. "And it's high now, and as it starts rocking backward, it starts falling to the side, it's also falling forward."

An energy-efficient approach

The side-to-side waddle is obvious. But penguins -- as well as other animals and people, for that matter -- also waddle forward and backward.

"We can't look at just the side-to-side movement," says Griffin, "but in terms of the combined side-to-side and forward movement, penguins conserved up to 80 percent of the mechanical energy required for walking. This was quite high, because other measurements for humans and other birds have found that they recovered only up to 70 percent of the mechanical energy."

People may find it amusing, but Griffin says a penguin's waddle is more efficient than a human's walk.