Iceberg Was an Early Test for Adelies

Seven years ago, the largest iceberg in recorded history broke off Antarctica’s Ross Ice Shelf, a chunk of ice slightly larger than the island of Jamaica. For the Adelie penguins of Cape Royds, the iceberg soon would present a test of their ability to adapt to a changed environment.

After calving from the shelf, the iceberg broke in two and the larger piece slowly floated hundreds of miles west, reaching Cape Royds in early 2001. It lodged itself on the sea floor just north of the cape, next to a smaller chunk of ice that had arrived earlier.

The Adelie colony had just left on its annual nine-month winter migration. When the birds returned for the breeding season in October, they found their way blocked by the icebergs while still far out at sea. To get to their nesting ground, the penguins had to walk 50 miles or more around the bergs on jammed-up sea ice.

Slow and clumsy on their feet, the birds arrived exhausted, said biologist David Ainley. When the females left the nests to seek food in open water, leaving the males to incubate the eggs, they had to traverse the 50 miles all over again.

“The females walked out and never came back,” said Ainley. “They didn’t want to make the trip again.”

The males stayed with the eggs for weeks, he said, but when the females failed to return, the males “abandoned the eggs in the nests.”

The icebergs remained for four years before floating off, giving Ainley a chance to observe how the penguins reacted in subsequent breeding seasons.

Older Adelie pairs, he found, stubbornly kept returning to familiar ground even though fewer chicks hatched because of the difficult conditions. The colony, which had 4,000 breeding pairs in 2002 and was one of the fastest growing in Antarctica, now has barely half that number.

But many younger penguins abandoned Royds to join colonies miles away that were not blocked by the icebergs.

Ainley said he sees a lesson in this for the future. If global warming melts the ice around the Adelies’ traditional territories so severely that it can no longer support them, some will simply perish.

But young pairs may head south, finding new territories in places that used to be too cold for penguins. That, Ainley said, may extend the species’ survival _ at least for a time.

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