Despite their pot-bellied profile and waddling gait, Antarctic penguins have weathered the challenges of one of the harshest climates on Earth for millennia. Three of those species—the Adélie, chinstrap, and gentoo—were also able to tolerate, if not flourish under, a warming event that came as ice sheets began to shrink, says a new study.

They were climate change "winners," the authors write. About 15,000 to 20,000 years ago, the retreating ice exposed expanses of bare ground that the penguins could build nests on, allowing them to expand their populations.

This historical perspective is helping researchers to understand the penguins' current situation in western Antarctica. (See "West Antarctic Glaciers Collapsing, Adding to Sea-Level Rise.")

The warming that researchers are now measuring on the Antarctic Peninsula is approaching the limits of what these penguin species experienced in the past, says Gemma Clucas, a doctoral student at the University of Southampton in the United Kingdom and lead author of the new paper. "We're seeing a very different response [from them now.]"

Genetic analysis of 249 gentoo, 166 chinstrap, and 122 Adélie penguins showed that all three populations expanded after the last glacial maximum—when the ice sheets were at their greatest extent—the researchers report today in the journal Scientific Reports. But only gentoo penguins seem to be holding their own against current warming trends in the western Antarctic. The other two species are in decline.

Too Much and Not Enough

"You can have too little ice and too much ice, and both of these are bad," says Jefferson Hinke, an ecologist with the U.S. National Oceanic and Atmospheric Administration's Southwest Fisheries Science Center in La Jolla, California.

In the past, the problem was a lack of real estate. During the last glacial maximum, there was 100 percent more ice in the sea surrounding Antarctica, severely restricting access to the ocean, which penguins depend on for food. Glaciers also covered the bare ground, where they lay their eggs and raise their young. It wasn't until the ice started melting that the penguin populations began to do better.

"Now we have too little ice," says Hinke, who was not involved in the study, "and the ecological consequences of that are that species like Adélie and chinstraps aren't doing too well." However, unlike the past, the problem for penguins now is a dwindling food supply.

Adélie and chinstrap penguins rely mainly on krill, which has been declining due to retreating sea ice, which the shrimplike animals need to grow. Commercial fishing for krill, along with a resurgence of whales that prey on the tiny animals, have further reduced krill populations. Gentoo penguins are likely doing better because they have a more flexible diet, which includes fish and some squid, in addition to krill. (See also "Penguin Numbers Plummeting—Whales Partly to Blame?")

Nothing Lasts Forever

"These species are a lot more robust than we sometimes give them credit for," says Heather Lynch, a population ecologist at Stony Brook University in New York who contributed data to the study. Researchers worry when species are forced to shift their ranges, she says, but this paper shows that these penguin species can come through those changes.

However, "there have been reversals of fortune in the past," Lynch says. The Adélie and chinstrap penguins are evidence of that. Even though the gentoo penguins seem to be doing OK now, "there's no guarantee that that will last forever."