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The penguin barometer

by Laura Durnford

10-11-2003

Two Adelies guard empty nests in a dying colony This report was featured in Research File. Listen to the programme in full.(29:30)

On a grey outcrop overlooking a small, gravelled valley, two Adelie penguins honk and wheeze. Thirty years ago this place resounded to the noise of around 600 birds, squabbling and working to build nests and raise their young. As occupants of one of the places most severely effected by global warming, this species is a barometer of nature's well-being worldwide; these two lone birds are the last remnants of their population.

"When they disappear, that's it for this entire colony," says Bill Fraser, a biologist who's been working here on the Antarctic Peninsula, 1000 km below the tip of South America, for about 30 years. "There were just so many of those birds around," he recalls, "you could not go anywhere without seeing hundreds to thousands of Adelies".

In the neighbourhood of Palmer Station, an American research base where Dr Fraser works, more than 30,000 adults and around 20,000 chicks used to fill the air with their clamour. But in this region, which has warmed more than almost anywhere else on Earth, barely 8,000 birds now survive.

Persistent beasts
The knee-high creatures spend most of the year on ice-floes, fishing for shrimp-like krill. But during the brief Antarctic summer they congregate on islands and build nests from gravel, ready to breed. They're so loyal to their customary sites, they keep going back even once conditions have become unsuitable for nesting. "Those two penguins return and make a nesting attempt every year," Dr Fraser gestures to the outcrop. "They'll continue until they die from over-winter conditions, or predators get them or – who knows – they die of old age."

Bill Fraser at work

Despite their best efforts, these birds have failed to rear young for the past few years because of flooding.

It's taken Dr Fraser and his colleagues decades of observation to spot the pattern of events causing the Adelies' decline; snow persisting on the ground later into the year prevents the birds from being able to make proper gravel nests on dry ground. Instead, they try building their stony homes on the snow.

But when the frozen surface melts, the water inundates the nests, dooming the unhatched chicks or, in cases where the eggs have already hatched, the young nestlings.

"They need the timing of conditions to occur in a precise sequence," explains Dr Fraser. "If the snow is too deep, their physiology doesn't allow them to wait out the melt."

Lifting lids
But how is global warming responsible for more snow? Well, normally the surface of the ocean surrounding Antarctica would freeze during the winter, literally keeping a lid on moisture, which would otherwise escape into the air.

The south side of Torgersen island where almost all Adelie colonies have disappeared. Now the only birds are at the high points where the snow melts first.

Higher temperatures inhibit the formation of this icy barrier so "during the winter and spring you have more open ocean exposed to the atmosphere. That ocean is obviously evaporating some amount of water vapour which then condenses and falls as snow."

Bill Fraser says that although Adelie penguins elsewhere in Antarctica are still doing fine, the birds in this warmed region serve as an ‘early warning system' for the rest of the natural world – and the prognosis isn't good: "We're saying that Adelies are likely to be locally extinct in the next 20 years."

photographs by Daniel Grossman
 

Links

NSF US Antarctic Program, 2002-2003 Adelie Penguin

Tags: adelie, adelies, antarctic, barometer, Penguin

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