Birds starve in warmer seas

By SIMON COLLINS science reporter

Seabirds on New Zealand's subantarctic islands are starving as warming waters drive away the tiny shrimp-like krill that they feed on.

Numbers of rockhopper penguins, a species with brilliant yellow eyebrows which nest on the rocks of windblown Campbell Island, 800km south of Stewart Island, have dropped by more than 95 per cent since the 1940s.

A breed of albatross called grey-headed mollymawks has declined by 84 per cent, muttonbirds are down by a third and elephant seals by about half.

A new study by the National Institute of Water and Atmospheric Research (Niwa) has found that the collapse of the rockhopper penguin population is due to the birds "being unable to find enough food in a less productive marine ecosystem".

"The cause is reduced productivity of the ocean where they are feeding," said Niwa scientist Paul Sagar.

"They eat mainly krill but they do also eat small fish and squid."

The research measured the amount of such penguin-food in the sea over the past 120 years by analysing feathers taken from rockhoppers alive today and from 45 museum specimens from the Antipodes and Campbell Island.

It found that the proportion of carbon atoms with one extra neutron - weighing slightly more than a standard carbon atom - dropped in the bird specimens taken between 1940 and today.

This showed that there must have been declining numbers of the phytoplankton, or algae, which extract the heavy carbon from the sea and pass it up the food chain to krill and eventually to the rockhoppers.

Mr Sagar said more research was needed to find out why the phytoplankton had declined, but some scientists believed it was due to the water becoming too warm for a species adapted to the subantarctic.

"It could be a long-run natural cycle, with the possibility that polar water coming up from the south may not be coming as far north as it used to," he said. "It could be that the position of the currents has changed so the productive areas have moved further south or north, away from where the penguins are feeding.

"If it's happening over such a long time, I wouldn't put it down specifically to global warming."

He said the study used the rockhoppers as an "indicator species", because it was likely that the same changes in climate and phytoplankton were also causing the decline in other birds.

A recent Otago University study had found that muttonbird numbers had dropped by a third on one of the main breeding islands.

Conservation Department scientist Peter Moore, who studied the rockhoppers on Campbell Island in 1996, said their numbers plunged from 1.6 million breeding pairs in 1942 to 103,000 pairs in 1985 and had continued to fall at a similar rate since.

Mr Sagar said there was evidence that some of the adult birds were feeding better quality food to their chicks, while their own diet declined. But Mr Moore said the orphaned chicks often died too.

In an Otago case in 1990, many surviving chicks from a yellow-eyed penguin colony were fed and reared by humans after their parents died. But after the chicks were released, 99 per cent of them were never seen again.

Mr Sagar is going back to the Antipodes next month and to Campbell Island in January to carry out further research, including an attempt to tag penguins to study where they feed and to check whether they really are feeding their chicks better than themselves.

The research will add to international studies which show declining rockhopper penguin numbers in other subantarctic islands in the Falklands off Argentina and the Kerguelen Islands south of India.

Australian studies have also shown a big drop in elephant seals on Macquarie Island south of New Zealand.

But Mr Moore said this might be an effect of the seal population "overshooting" its food supply in a dramatic recovery after commercial sealing ended early last century.

Penguins


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