For some penguins, less ice means stark choices

It isn't life-as-usual on the Antarctic Peninsula. Particularly, if you're a penguin.

Winter pack ice - which sometimes extends halfway to South America - is tending to cover less and less area. In the 1950s, researchers could expect extensive pack ice in 4 out of 5 winters. Now, the rate is down to 1 or 2 every 5 years.

Adelie penguins rely on pack ice and are declining, while Chinstrap and Gentoo penguins (which prefer open water) are expanding their habitat range. "We're watching one ecosystem replace another," says William Fraser of Montana State University. "It's hard to say if that's good or bad, but it's very dramatic."

Warmer temperatures have also meant greater snowfall, and many Adelie colonies around Palmer Station have gone extinct for lack of dry land to nest on. Last year, the spring snow cover was so thick many penguins couldn't find pebbles with which to build their nests. Seals come ashore for naps, melting the snow underneath them. "As soon as the seals went back into the water, the Adelies rushed over across the ice to collect all the pebbles," says marine biologist Peter Duley, part of Fraser's team here.

Penguins are also plagued by an invasion of ticks, which are now able to survive the winter to hatch in the spring. Exponential increases in the number of fur and elephant seals in the area (both prefer open water) have caused many penguin nesting sites to be crushed by the napping beasts.

"We're changing the face of the Antarctic," says Beth Clark, director of the Washington-based Antarctica Project, who says the climate change is caused by human greenhouse emissions. "If you realize that this is a continent that's remained largely unchanged for millennia, you can begin to understand how dramatic the effects of climate change can be."