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February 2003

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Field Dispatch

Field Dispatch

Research and Exploration

Birds That Go to Extremes

When shorebirds called knots fly south for the winter, they face an epic migration from their Arctic breeding grounds. Different populations of these far-flung members of the sandpiper clan disperse to distant havens such as Great Britain, West Africa, even Tierra del Fuego.

Most shorebirds must travel far to find suitable winter feeding grounds. But knots are marathoners, overflying vast stretches of unsuitable terrain while seeking coastal tidal flats that they need for food.

One group of knots wings 7,500 miles (12,000 kilometers) from the Siberian Arctic to Roebuck Bay on Australia's northwestern coast. Theunis Piersma, an evolutionary biologist with the Netherlands Institute for Sea Research, investigates how the knots cope with the oppressive austral summer, a hemisphere away from Siberia.

About 170,000 shorebirds a year migrate to Roebuck Bay, including the two species studied by Piersma and his colleagues: red knots and great knots.

"From February through April the bay is distressingly hot and humid," says Piersma. "We think that Arctic-breeding shorebirds must find these conditions extremely difficult."

How hot are the knots? Their body temperatures can reach well above 100°F (38°C). They'll pant and raise feathers on their backs, exposing skin so heat can dissipate. The birds often wade in shallow water to shed heat. But nothing is cool at Roebuck Bay.

"When the tide comes in, you expect the water to give you relief when it flows around your ankles," says Piersma. "Quite the contrary—it's as if somebody poured warm coffee around your feet." The water can exceed 90°F (32°C).

Paradoxically, the knots make things worse by simply fulfilling their purpose: to get fat. When they depart for the Arctic, they first fly 3,400 miles (5,500 kilometers) in a few days to lay over on the coast of China. So in Australia they must fill their energy tanks to the brim by gorging on mollusks and other invertebrates. That means building up muscle and putting on fat, which makes it even harder to lose heat.

In Roebuck Bay, Piersma and his team studied how knots prepared for their return trip to the Arctic. They attached color bands to the legs of more than a hundred birds for visual tracking. They also tagged the birds with numbered metal rings to identify them if recaptured later at Roebuck Bay. With birds in hand they used ultrasound to measure stomach and flight muscles. They examined the birds as they changed from winter plumage to their reddish summer breeding coats, which indicates migration readiness.

The team attached radio transmitters to 25 great knots and 23 red knots, then tracked the birds with handheld receivers and with 14 automatic radiotracking stations around the bay. The receivers collected more than 5.5 million bits of data.

In some cases they recorded virtual electronic diaries of individual knots. One great knot was captured on March 4 in fine condition, already showing 90 percent of breeding plumage. Upon release he stayed near the beach where he was caught. "He left on March 29, one of the first radio-tagged birds to migrate," says Piersma.

But red knots—slightly smaller than their cousins—were stragglers. "One was with us a long time," Piersma recalls. It departed on May 7. "Such a late migration leaves the red knots only four to five weeks to arrive in the Arctic for their short breeding season. Great knots take about eight weeks to make the journey."

Knots can't build up their reserves for the trip without Roebuck Bay's bouillabaisse. But its marine life is threatened by Broome, a center for tourism on the bay's edge. Beachgoers already disturb roosting shorebirds. Piersma and his colleagues have recommended ecological management rules for the bay—"to help people and their avian fellow travelers coexist for a long time to come."

—John L. Eliot

Web Links

WBK English
Read about the knots of South Korea, and what this organization is doing to help conserve them.

Birds Australia
Hear bird calls and learn about threatened Australian bird species. This site provides links to other bird resources on the Internet. Birds Australia is part of a global partnership called BirdLife International.

BirdLife International
Learn about threatened bird species and habitats on a global scale, read recent bird news from around the world, and find out about international conservation events.

Netherlands Institute for Sea Research
Find more in-depth sources about research on shorebirds and other types of marine life.

Broome Bird Observatory
Theunis Piersma's team used the Broome Bird Observatory as a base for their research on knots in Roebuck Bay, Australia. It is a public facility, managed by Birds Australia, where visitors can learn about local birds and their habitats.

Department of Conservation and Land Management, Government of Western Australia
The Department of Conservation and Land Management is the local partner and supporter of Piersma's work in Roebuck Bay. It manages Western Australia's parks, state forests, and reserves. Learn about the region's plants and animals, find out about recreation opportunities, and catch up on the latest news and events related to conservation in the region.

Free World Map

Del Hoyo, Josep, and others, eds. Handbook of the Birds of the World, vol. 3. Lynx Edicions, 1996.

Piersma, Theunis. "Waders in winter: blowing hot and cold," Birds (Autumn 1994), 64-6.

Piersma, Theunis. "Wader flyways: realm of the long journeys," Birds (Summer 1994), 53-7.

Piersma, Theunis, and A. J. Baker. "Life history characteristics and the conservation of migratory shorebirds." In Behaviour and Conservation, eds. L. M. Gosling and W. J. Sutherland. Cambridge University Press, 2000.


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