McMURDO, ANTARCTICA — With the aplomb of a slapstick comedian, the penguin waddled across the Ross Ice Shelf, moving toward open water in a series of determined slips, slides and belly flops.
Dressed in formal featherwear, the black-and-white bird struggled over the hard ridges of wind-rippled snow. But each step forward seemed more exhausting than the last. Finally, the penguin plopped down on its stomach, arched back its head and kicked its paddle-like feet in a flurry of frustration.
To all appearances, this worn-out waddler--so graceful underwater--was just out of its element on the surface.
No other bird dives deeper than the emperor penguin--as much as 1,500 feet for as long as 18 minutes. No creature seems so at home in two of Earth's most inhospitable environments--the frigid depths of the Southern Ocean that isolates Antarctica and the vast sea ice that surrounds it.
And no other creature seems to do so much work putting one foot in front of the other.
Penguins expend twice as much energy in walking a given distance as any other animal of the same weight, bobbing from side to side while also rocking back and forth as they move, researchers at UC Berkeley have determined. In this way, emperor penguins often travel 100 miles across the ice in conditions that would doom almost any other animal, from temperatures that drop to 100 degrees below zero to winds that top 200 mph.
But the creature's awkward amble is far more energy-efficient than anyone suspected.
Biologist Timothy M. Griffin at the UC Berkeley Locomotion Laboratory recently discovered that, as a matter of biomechanics, the penguin's distinctive gait is one of the most efficient among all creatures that walk the Earth--far more efficient than human walking.
The penguin does work harder walking, but not because it waddles. Waddling actually conserves energy. The penguin's problem is that its legs are just too short for easy walking. As a result, its leg muscles must generate extra force very quickly when it walks, compared with those of other birds of similar size, and waddling helps compensate for that extra effort, Griffin and his colleagues found.
This new insight into the unexpected ergonomics of the penguin design for living illustrates how little scientists have been able to learn of this most unusual flightless bird.
So much of the emperor penguin's life takes place behind the curtain of fierce blizzards and midwinter darkness on the isolation of the Antarctic sea ice that many details of how they and other penguins walk, feed, behave, develop and breed still are unknown.
To study the biomechanics of the emperor penguin's walk, the UC Berkeley researchers worked in the penguin exhibit at SeaWorld in San Diego. There, the team enticed the curious birds across a special force platform that measured the side-to-side and fore-and-aft forces that the penguins exert while walking, plus the vertical forces for supporting their weight.
Evidently, Griffin said, the emperor penguins have made an evolutionary trade-off between the extremes of the deep sea and the surface ice that they call home. Their short legs make them streamlined swimmers and divers, even if those same legs also make them ungainly walkers. The short legs may also help reduce heat loss, especially while the emperors are incubating their eggs on the sea ice in winter.
Adapted for the Ocean
Waddling is just one way the biology of the penguin embodies one of nature's most sophisticated balancing acts.
In all, there are 18 species of penguin, but only the emperors and their slightly more diminutive cousins, the Adelie penguins, make their homes in colonies around the coast of the Ross Sea, where McMurdo, the largest U.S. National Science Foundation research station in Antarctica, is located.
Here, penguins are revealed as a collection of unexpected adaptations, from their streamlined, waterproof swimsuits of interlocked feathers to their solid, dense bones that help them overcome a more conventional bird's natural buoyancy.
So sleek has nature made these birds that they have among the most streamlined body shapes ever gauged.
A swimming chinstrap penguin measuring more than seven inches wide, for instance, slips through the water with less resistance than a pebble the size of a quarter, according to biologist Gerald Kooyman at UC San Diego's Scripps Institution of Oceanography, who has studied penguins in Antarctica for decades.
Some species spend so much time at sea that they have been found with barnacles on their tails.
The king penguin feeds only at sea, yet must somehow support itself and its young when it comes onto the ice to breed. Researchers at the Centre National de la Recherche Scientifique in Strasbourg, France, recently discovered that the male king penguin can preserve undigested food in its stomach for as long as three weeks, so that it can serve as a living larder for the chicks.