Emperor Penguins Are Teeming in Antarctica

Using satellites, researchers counted Antarctica's emperor penguins at 46 colonies like this one near the Halley Research Station, finding numbers twice as high as previously thought.

By ROBERT LEE HOTZ

Antarctica has twice as many emperor penguins as scientists had thought, according to a new study using satellite imagery in the first comprehensive survey of one of the world's most iconic birds.

British and U.S. geospatial mapping experts reported Friday in the journal PLoS One that they had counted 595,000 emperor penguins living in 46 colonies along the coast of Antarctica, compared with previous estimates of 270,000 to 350,000 penguins based on surveys of just five colonies. The researchers also discovered four previously unknown emperor-penguin colonies and confirmed the location of three others.

"It is good news from a conservation point of view," said geographer Peter Fretwell at the British Antarctic Survey in Cambridge, England, who led the penguin satellite census. "This is the first comprehensive census of a species taken from space."

Although all of Antarctica's wildlife is protected by international treaty, the emperor penguins are not an officially endangered species. But they are considered a bellwether of any future climate changes in Antarctica because their icy habitat is so sensitive to rising temperatures.

To track these elusive penguins from space, Mr. Fretwell and his colleagues used high-resolution commercial imagery from the Quickbird and WorldView-2 satellites operated by DigitalGlobe Inc. in Longmont, Colo. The combined satellite sensors could detect the birds, dressed by nature in formal black-and-white feather-wear, against the backdrop of 5.4 million square miles of ice.

Hampered by Antarctica's forbidding conditions, field biologists have tried and failed for more than 50 years to get an accurate count of these curious, 90-pound birds who make themselves at home in one of Earth's most inhospitable places. They dive more deeply than any other bird, as deep as 1,800 feet, and breed on ice shelves during the long night of the Antarctic winter, when temperatures plunge to minus 58 degrees Fahrenheit.

Viewed from orbit 300 miles or more above Earth, each four-foot-high penguin takes up just about one pixel in a precision satellite image.


In the new study, scientists first located the emperor-penguin breeding colonies by scanning satellite images for telltale patches of reddish-brown penguin guano on the ice, which are readily spotted from space. By combining monochromatic and color images to sharpen the focus of the satellite imagery, the science teams were able to then differentiate between birds, guano and shadow.

"From outer space, all you can see at first is ice and a little brown stain," said research fellow Michelle LaRue at the University of Minnesota's Polar Geospatial Center. "Then we are able to zoom right in. The penguins are these itty-bitty black dots that pepper the ice."

Previous attempts to count emperor penguins systematically have been thrown off because field biologists could survey the penguin rookeries only during the extended daylight of the Antarctic summer, when conditions are relatively balmy and the penguins usually are scattered, feeding at sea. Some colonies had not been counted for decades and many more had never been surveyed at all, the researchers said.

By using satellites, the researchers were able to conduct their census when the emperor penguins were still gathered at their breeding grounds to tend their young.

"The beauty of the satellites is that you can count all the colonies around the Antarctic coastline at one go in one breeding season," said Mr. Fretwell.

The researchers hope that their census, funded by the U.S. National Science Foundation, will become the benchmark against which the future health of the species can be measured.

"For penguins, it is particularly important, because there are predictions that we might lose emperor-penguin colonies due to changing environmental conditions," Mr. Fretwell said. "We hope to continue monitoring the emperor population over the coming seasons to see if it is stable or if it declines."

Write to Robert Lee Hotz at sciencejournal@wsj.com

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