By Helen Briggs BBC News Online science reporter

Descendants of Emperor penguins visited by members of Scott's doomed South Pole expedition are facing a grave danger.

Two scientists who visited the Antarctic site last month say the birds are struggling to cope with the effects of two giant icebergs.

Emperor penguins nest in a very harsh and a very dynamic environment

Dr Keith Reid, British Antarctic Survey

The shore where they live and breed has been broken up by the impact of the ice.

The colony of thousands of penguins has split up into at least five groups and numbers are declining.

"It's certain that the number of breeding birds is way down [from previous years]," said Gerald Kooyman of the Scripps Institution of Oceanography in La Jolla, California, US.

Food shortage

When he visited Cape Crozier in October he found that the penguins' habitat had been disturbed by the drift of two icebergs known as B-15 and C-19.

Penguins have relatively few chicks compared with other species

The adults were running out of food for their chicks and some birds may have been crushed by the ice.

"We could not find one group," said Dr Kooyman. "It looks like they were in an ice canyon that was eliminated by two ice plates running together."

Kooyman, and colleague Paul Ponganis, will compare notes on the fate of the colony with other researchers studying Adelie penguins facing similar hazards.

However, the risk appears to be receding because the icebergs seem to be moving elsewhere.

According to Dr Keith Reid of the British Antarctic survey in Cambridge, UK, the bird is well adapted to surviving changes to the extreme environment in which it lives.

He told BBC News Online: "Emperor penguins nest in a very harsh and a very dynamic environment.

"The changes in the ice distribution around this colony and the changes in the birds is just an example of the nature of that environment."

Perilous journey

The Emperor penguins are descendants of those visited by Antarctic explorers early in the 20th Century.

Apsley Cherry-Garrard was one of three members of Robert Falcon Scott's team who visited Cape Crozier in 1911.

He recorded the experience in a classic travel book, The Worst Journey In The World.

Cherry-Garrard, Bill Wilson and Henry "Birdie" Bowers hauled a sledge 100 kilometres (60 miles) in complete darkness and sub-zero temperatures to collect penguin eggs from Cape Crozier.

They almost died during the journey, when they were trapped in their tent for three days during a mighty winter storm.

Cherry-Garrard's two colleagues later perished along with Robert Falcon Scott in the return journey from the South Pole.

Some say Cherry-Garrard never fully recovered from the ordeal of discovering the bodies of Scott's polar party.

His scientific quest went unrecognised for many years, as museums refused to put the eggs on display.