"The Antarctic penguins already have a long march behind them," Anna Reynolds, deputy director of WWF's Global Climate Change Programme, said in a statement at the Bali climate talks.

"Now it seems these icons of the Antarctic will have to face an extremely tough battle to adapt to the unprecedented rate of climate change."

The report, "Antarctic Penguins and Climate Change", said sea ice covered 40 per cent less area than it did 26 years ago off the West Antarctic Peninsula, leading to a fall in stocks of krill, the main source of food for the chinstrap and gentoo penguins.

In the northwestern coast of the Antarctic peninsula, where warming has been fastest, populations of adelie penguins have dropped by 65 percent over the past 25 years, it said.

The number of chinstraps decreased by 30 to 66 percent in some colonies, as less food made it more difficult for the young to survive, while the emperor penguin has seen some of its colonies halve in size over the past half a century.

Warmer temperatures and stronger winds mean the penguins had to raise their chicks on increasingly thinner sea ice which tends to break off early while many eggs and chicks have been blown away before they were able to survive on their own.

Scientists have predicted that global temperatures could rise sharply this century, raising world sea levels and bringing more extreme weather.

A 2005 study showed that most glaciers on the Antarctic peninsular were in headlong retreat because of climate change -- and the speed was rising. Scientists say that most of the rest of the ice on the giant continent seems to be stable.

"The food web of Antarctica, and thus the survival of penguins and many other species, is bound up in the future of the sea ice," said James P. Leape, director general of WWF International.