February 10, 2003
The Adelies' Long Farewell
Adelie penguins around Palmer Station are in trouble. Penguin researcher Bill Fraser, who has been visiting the region on and off for 30 years, has documented a dramatic reduction in their numbers. Overall, the number of breeding pairs has dropped to about one-quarter of its level when he first visited Antarctica in 1974. Many individual colonies have simply disappeared. Fraser predicts there will be no Adelies nesting there within a decade.
|The summit of the rocky ridge that bisects Cormorant Island
Adelies are superbly equipped to overcome some of the world's harshest conditions. They are one of only two penguin species that live exclusively in Antarctica (emperor penguins being the other). They spend 90% of their lives either in the water or on pack ice, masses of icebergs squeezed together. They can dive for food for hours at a time reaching depths exceeding 500 feet. During the breeding season they sometimes make foraging trips of more than 100 miles, swimming through waters below 32 degrees Fahrenheit. Ocean researchers have discovered that the friction, or drag, Adelies experience as they swim is considerably less than the drag on what they call the "ideal spindle" supposedly the most efficient shape for an object moving through water.
Bill Fraser says that the perfect adaptation Adelies have achieved to their Antarctic habitat has come at a price: a difficulty coping with change. Not long ago Fraser took me on a half-day island-hopping tour to show me why he thinks global warming is responsible for the decline of his Adelies. Our first stop is Cormorant Island. A small rocky outcrop with a high ridge in the center, the island is the home of a small colony of about three dozen cormorants as well as several colonies of Adelies. It was here that he came up with what he calls the "landscape" theory of the impact of climate change on Adelie penguins. Some of the best examples of how the theory works are here.
We tie up our zodiac and cross the island, passing several raucous Adelie colonies.
Adelie colonies are noisy places because adults are constantly marking their territory.
Moreover, when one adult returns from foraging it makes special calls that, like
gang handshakes, permit mates to recognize each other. Older chicks also contribute
to the clamor, noisily begging for food from their parents. Fraser leaps from
slippery stone to slippery stone till we reach the island's other side. This side
is separated from where we landed by a ridge of bare rock. In contrast to the
other side, there are no Adelies here. Fraser explains that the orientation of
Cormorant Island's rocky spine is east-west, perpendicular to the direction of
the prevailing winds which generally blow from the north. Snow that falls on the
northern (windward) side of the island is dispersed and melts quickly in spring.
But on this southern‹leeward‹side where we are standing, deep drifts build up.
When spring comes these drifts, get relatively little sunlight (southern exposures
are warmest in the northern hemisphere but in the southern hemisphere, southern
slopes are comparatively cool). So they melt relatively late. Sure enough, last
winter's drifts are still here on the south side even though the austral (southern
hemisphere) summer is nearly over and the rest of the island is snow-free.
Though Adelies live much of their lives on ice, they need bare ground to breed. That makes the leeward side of this island unsuitable for these birds; the snow doesn't melt in time for them to build nests and lay eggs.
That's why there are no birds here, says Fraser. The researcher thinks this part of Cormorant Island has probably been free of Adelies for hundreds of years. Now Fraser turns around and faces the land more favorable for Adelie colonies. Each colony, he points out, is close to the summit of one of the many low knolls on the isle. Surrounding every one is a broad band of stones about the size of silver dollars. These patio-like rings of pebbles are clean, unlike the colonies they encircle‹which are tinted the rusty-red of penguin guano. Fraser says these clean stones were covered by nesting penguins when he began his research three decades ago. The small, round stones were carried there by penguins, to line their nests. Close-up the pebbles are burnished to a smooth finish by the polishing effect of generations of penguin feet.
Fraser says today's colonies are the diminished remnants of those he saw when he arrived in 1974 as a graduate student. They have been declining ever since, he says, yet for years no one knew why. Fraser long suspected that climate warming was the culprit. The average summer temperature in the Antarctic Peninsula has risen by 9 degrees Fahrenheit in the last 50 years.
But he couldn't see how this warming affected the Adelies. After years of pondering what was going on Fraser had an insight. What Fraser realized was that warmer climate was causing heavier snowfall. It doesn't make sense at first, but warmer air holds more water. Also the Antarctic Peninsula has experienced less winter sea ice in recent years. Sea ice, which creates a solid shelf extending from land far into the ocean, acts like a lid on the ocean, reducing the amount of evaporation into the air. Less sea ice and warmer air both mean more precipitation, which in this area means more snow.
This additional snow, Fraser could see was making was making areas downwind from many hilltops unsuitable for Adelies. Although the area downwind from the small knolls on Cormorant Island sites were once snow-free early enough for penguins to nest, now the snow doesn't melt in time for the birds to raise healthy chicks. He says that Adelies wait for ground to be bare. But the greater snowfall created new areas where bare ground came too late for Adelies to raise healthy chicks; by the time rocks poke through snow drifts the optimal time for breeding has past.
When the adult birds are unable to reproduce or when their chicks are not healthy and don't survive, a colony wastes away. Older birds simply aren't replaced by the next generation. Adelies are so loyal to their colony they won't search more suitable land. The researcher says that other factors may also be having an impact on the Adelies. Whatever might be the cause,
Fraser says unless something dramatic changes it won't be long before Adelies are completely gone from the Palmer region. Fortunately as a species Adelie penguins are not in imminent danger: they are doing fine elsewhere in Antarctica. And when they have gone, the islands around Palmer will not be barren. Two other penguin species, chinstrap and gentoo penguins are slowly replacing the Adelies. Fraser says he'll miss his subjects. But the importance of this closing chapter of these colonies is that something is going wrong here in the Antarctic Peninsula.
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