AUSTRALIA: Mutton birds or puffins

Giant tiger snakes as long as a man's arm and with heads the size of a closed fist live on Great Dog Island. So it is always with some trepidation that La Trobe University researcher Mark Carey pushes his arm down the burrows where the mutton birds nest - in case a tiger is there as well.

"I have a fear of snakes," Carey says. "And if students are with me on the island, the one rule is that the 's' word is not to be spoken unless there's one of them about..."

When he puts his arm down a burrow, he wears a leather glove on his 'catching hand' and two big long-sleeved shirts that he tapes the cuffs to because once a snake went up the sleeve of a field worker.

"That was before my time and although I've been there for six seasons catching birds, I've never met a snake down a burrow. They are on the rookery and I've seen them go down the burrows but never seen one come out..."

As a teacher and researcher in La Trobe's department of environmental management & ecology since 2006, Carey spends up to four months every year on Great Dog Island. He estimates that in the past six years, he has spent more than 12 months of his life down there.

Carey is completing his PhD into aspects of the life of the mutton bird, more correctly known as short-tailed shearwaters but which also go under the wonderful Latin name of Puffinus tenuirostris.

Great Dog Island is in the Furneaux Group, off the north-east coast of Tasmania. It covers almost 400 hectares and is uninhabited apart from the big tiger and copperhead snakes and the small white-lipped snake.

Of course there are also millions of mutton birds whose young the tiger snakes feed on. The island is Tasmania's third largest mutton bird rookery and they arrive late each year to breed and lay their one egg in the burrows.

"Their laying is extraordinarily synchronous, with 85% of eggs laid within three days around 25-26 November," Carey says. "Chicks hatch from 10 January onwards after a 53 day incubation period and they fledge in the last half of April to the first week of May."

He says the chicks remain in their burrows for three and half months and "try not to get eaten by the tigers which have to get them young because they grow fast and after two weeks are too big for the snake to swallow".

"There is always a glut of these beautiful chicks and the snakes go crazy trying to eat as many as they can. Although the great majority survive, they are abandoned by their parents and have to learn to feed and to fly by themselves, yet somehow they know how to migrate to the northern hemisphere."

In one experiment, Carey attached tiny 'data loggers' to the legs of 27 mutton birds before they began their migration. The 1.8 gram loggers were developed by researchers at the British Antarctic Survey headquarters in Britain's Cambridge University and record the times of sunset and sunrise each day (to enable latitude and longitude to be calculated) as well as how long the bird was in the air or on the water.

A year later after recapturing 20 of the birds, Carey went to Cambridge to download the data and begin his analysis. This revealed that after breeding, the birds left the Furneaux Group and headed south below the Antarctic Convergence - a region rich in Antarctic krill the shearwaters feed on - to build up enough reserves to undertake the long-haul flight.

They began their long journey south of New Zealand, then flew north in great flocks up the western side of the Pacific Ocean to the coast of Japan and into the Bering Sea. Travelling at 800 kilometres a day, these small 600-gram birds covered the distance in about 12 days - "an incredible feat", as Carey says.

In fact, biologists have calculated a shearwater makes a round-trip of about 20,000 kilometres on its migration journey. And, because they live up to 30 years, an older shearwater might have travelled some 600,000 kilometres - or the distance to the moon and nearly halfway back again.

"The birds spend much of the time in the northern hemisphere summer in the Bering Sea or off the coast of Japan," Carey says. "On their return migration, they come down the central part of the Pacific, hit the Australian coast around Queensland and travel along the coast back to the colony."

Although they are shearwaters, the mutton bird name stems from their exploitation for food and oil since the 19th century. At its peak in the early 1900s, at least a million birds were taken each year but today perhaps 300,000 young are killed.

Part of Carey's research is to discover what impact his work with the birds has on their hatching success. An estimated 23 million short-tailed shearwaters breed around the coast of Australia but other species in the same family are in serious decline.

"Many populations are declining because their island breeding habitat is being lost or degraded as a result of human development and the introduction of mammalian predators," he says.

"They are also threatened by high levels of mortality caused by long-line fisheries and so disturbance by researchers that reduce their reproductive success could exacerbate the problem."

So after six years' close study of the mutton birds, what does he think of them? "I love them, I think they're amazing birds. They are long-lived, they form long-term pair bonds, they migrate extraordinary distances every year - they are an incredible species."

geoff.maslen@uw-news.com