May 14, 2001 -- Emperor penguins, the tallest among the penguin family, can't take the heat, French scientists said.
In a study published Thursday in Nature, the scientists showed that over the past 50 years, during which unusually warm temperatures swept over Antarctica's Southern Ocean, populations of emperor penguins have been dying — their numbers dropping by more than 50 percent.
According to data recorded since 1952, numbers of the normally hardy penguins, which can reach 3 feet in height and more than 65 pounds in weight, were devastated by a long period of warming in the region in the late 1970s. Populations of the penguins have now stabilized, but scientists suggest if warming trends continue, the penguins could be facing another decline.
"If global anomalies become more common, which is a possible scenario in the event of global warming, then emperor penguins would decline again," wrote Henri Weimerskirch of the Centre d'Etudes Biologiques in an e-mail interview with ABCNEWS.com.
Penguin Cold-Weather Gear
Emperor penguins are designed for cold weather. They sport a thick layer of blubber under their skin, covered by a dense layer of woolly down. Over this insulation the penguins wear a coat of overlapping feathers, made waterproof by a greasy coating.
But studies suggest warmer temperatures don't affect the penguins directly. Instead it kills off their main food source — krill.
Krill are tiny crustaceans resembling small shrimp that populate the Southern Ocean in vast swarms and provide the main diet for whales, seals and penguins. Young krill feed on algae living in sea ice. Since warmer temperatures reduce sea ice covering, populations of sea ice algae drop, krill starve and food supplies for larger species, including the emperor penguin, dwindle.
Other scientists, including Bill Fraser of Montana State University, have shown that populations of other, smaller penguins like the Chinstrap and Adelie were also depleted by the warming trend in the 1970s. Fraser claims these populations are still dropping by a rate of up to 40 percent since 1989 due to recent warming.
Antarctica has lost a quarter of its sea ice over the past 100 years, according to recent studies. This past winter alone, satellites have recorded a spate of icebergs, some as vast as the state of Connecticut, calving from the continent. Many of the icebergs have broken from the Antarctic Peninsula where temperatures have risen by about 2 ½ degrees over the past 50 years.
But scientists are divided over whether the shrinking coverage of ice is due to global warming or to a natural fluctuation in temperatures and ice levels.
No matter the causes, Weimerskirch and his co-author, Christophe Barbraud caution in their paper that it's important to monitor the trend — since at least emperor penguins clearly feel the heat.
"Our results indicate that emperor penguins may be very susceptible to environmental variability," they wrote.