Happy feat: penguins swim fifteen thousand kilometres in six months

Call it a happy feat.

New Zealand scientists have been astounded to find that two species of subantarctic penguin were able to travel 15,000km - equivalent to the distance between Auckland and Boston - over a stretch of just six months.

The insight was revealed by a tagging project observing nearly 100 subantarctic rockhopper and Snares penguins over winter in the Southern Ocean.

"If they are constantly moving this averages out at about 100km a day but you also have to add on to that the distances covered vertically as the birds dive to capture food," said the study's leader, National Institute of Water and Atmosphere seabird ecologist Dr David Thompson.

While the Snares penguin population on their craggy namesake islands was relatively stable, Campbell Island's rockhoppers had dwindled by at least 21 per cent since 1984, leaving just over 33,000 breeding pairs there.

The island was once the world's largest breeding colony of the colourful rockhoppers - the smallest of all penguin species and featured on the movies Happy Feet and Surf's Up - but between 1942 and 1984 the population dropped by about 94 per cent.

Researchers have been trying to understand what has caused the sharp decline, with big changes in their diet a suspected cause.

Thompson said the penguins' led an extreme lifestyle, taking them out into the ocean for long periods of time.

"They come to land to breed and when they finish that, go back out to sea where they feed up for a month," he said.

"Then they come back to land to sit and moult their feathers. During that period they don't eat at all."

Having virtually starved themselves, they then headed back out to sea in poor condition.

"They've grown a whole new set of feathers so their plumage is fantastic but it's quite demanding so they're really scrawny.

"We think winter is pretty important and that there is almost certainly something going on in the ocean causing the population to decline."

The tags attached to the birds had to be modified from fitting the long, skinny leg of an albatross to the short, stubby leg of a penguin.

Thompson and his colleagues also had to time their arrival on Campbell Island, 620km south of Stewart Island, with the end of the moulting season, just as the penguins were ready to leave for the winter.

Then they had to clamber down rock faces and steep cliffs to reach them.

Of the 90 penguins tagged for the project, about 80 returned the following spring when the tags were retrieved and data processing began.

Tracking their movements was an eye-opening exercise.

The Snares penguin headed exclusively west towards Australia, while the rockhoppers went east and covered a wider section of the ocean.

Several birds covered more than 15,000km over the winter.

The tags were also able to determine when the penguins were stationary, indicating they had stopped to dive for food or rest.

Thompson said this first tracking project had provided just a snapshot, but the work had to be start somewhere.

"We don't know what they're feeding on when they're away; we don't know if the amount of food available was more or less comparable to five or 10 years ago so this is very preliminary."

He plans to repeat the project and include other species, such as the erect crested penguin of the Antipodes Islands.

"The extra species will give us more information on how they relate to each other when they go away. It may be that they use different space, or it may be that populations of different islands get together at sea.

"Research like this is important to better understand what's important for penguins. It is possible that particular parts of the ocean may help them get through from one year to the next so we need to be able to identify those places."

"Prior to this study we didn't have a clue where rockhoppers went in the winter but the spaces they use in the ocean might be really important - not only for them but for scientists to better understand what is causing the population decline."