From the Antarctic: Iceberg collapse saves penguin colonies

By SIMON COLLINS at Scott Base

Nature has finally come to the rescue of four colonies of Antarctica's Adelie penguins which have been blocked off by a huge iceberg for the past two summers.

The 300km-long iceberg B-15, which calved off the Ross ice shelf in March 2000, has now broken up enough to let open seawater in as far as the southernmost Adelie colony at Cape Royds, 35km northwest of New Zealand's Scott Base.

About 2000 breeding pairs of Adelies are now nesting on a barren headland partially exposed to bone-chilling southerlies, where they and their ancestors have returned to breed for hundreds of years.

American penguin scientist David Ainley, who is camping at the site, says the numbers are still only about half the normal rollcall of penguins who nested there before B-15.

He believes there is still so much sea ice north of Cape Royds that many of the penguins could not get back this year from the subantarctic islands, 1000km to the north, where they go to avoid Antarctica's frozen winter.

Some penguins that he tagged at Cape Royds in past years turned up last year at Cape Crozier, 75km away on the other side of Ross Island, where there is a much bigger colony of about 150,000 breeding pairs.

Those that made it to Royds produced a total of only 150 chicks from around 3000 breeding pairs, a success rate of only 5 per cent.

"Reproductive success was a total bust," Dr Ainley said.

The females laid the eggs but they didn't come back, or came back too late to an empty nest.

Male and female penguins job-share the long, cold task of sitting on their eggs until they hatch.

Dr John Cockrem of Massey University, who is studying the Adelie penguins' reactions to stress, says the males take the first 20-day shift while the females go away to find food.

Then the females take their turn for a week while the males go out for food.

After that they take turns every day or so.

In the past two years, most of the chicks died before they were ready to hatch because the males left to mind the eggs in those first 20 days had to abandon the nest in order to find food for themselves before the females returned.

Ironically, both males and females still came back to the colony later, even though their chicks had died.

At the end of last summer there were 4000 pairs of penguins sitting round doing nothing, Dr Ainley said.

"For failed breeders, the way they maintain the pair bond and territory is to come back later in the season and keep house. Then they go off north for winter.

"For a pair that is successful, they don't really see one another after the chick becomes independent, until the next season."

Now that the sea has finally come in to the edge of the colony, both parents this year should be able to find the fish they need to feed themselves and their chicks.

Dr Ainley said icebergs as big as B-15 which block the penguins' access to their colonies have broken off the ice shelf naturally, perhaps every 50 to 100 years. They may explain why all 3 million Adelie penguins, spread right around Antarctica, are genetically almost identical, indicating a lot of interbreeding despite the fact that in normal times they invariably return to their home colonies.

Apparently, big icebergs force them to shift house.

It was not until B-15 that we had an explanation of why the gene pool is so homogeneous, Dr Ainley said.

It would have to happen only once every 1000 years to maintain that homogeneity.