The Mystery of the Migrating Swans
'FEW birds stir the imagination more than these," says Jay Sheppard. He's a biologist at the Washington, D.C.-based Wilderness Society. "If you see a migrating flock of them on a clear, cold night, they are like graceful ghosts against a full moon."
The sight of whistling swans in an autumn-night sky must have captivated people for centuries. But it wasn't until 30 years ago that anyone knew for sure where the migrating swans were coming from.
Whistling swans, also called tundra swans, are on the move again this month. Some 95,000 of them should land in Chesapeake Bay on America's East Coast by Halloween. A few weeks later, more will alight on the swamps of North Carolina. The birds will spend the winter feeding on grasses and small mollusks (spineless animals with shells, like snails and clams).
Among the migrating flocks are four-month-old youngsters making their first long flight. Their parents are teaching them the route: where to go, where to stop to rest and feed. Flocks may stay in one place for a time on their migration.
It took humans a long time to learn the mysteries of migration in general and tundra-swan migration in particular. Long ago, says Bill Reffalt, also of The Wilderness Society, "people used to think that every spring and fall birds went to the bottom of the ocean, into holes in the ground, or into trees."
By about 1900, people suspected that swans flew a long way every spring and fall. They wanted to find out how far and where. Small groups of bird-lovers got together and began "banding" birds. They put small colored rings around the birds' feet. By recording where the bird was banded and where it was next seen, they could track a particular bird's movement.
Famous bird artist John James Audubon was one of the first to band a bird. In the early 1800s, he wanted to know if a bird in his yard every year was the same one, coming back. (It was!)
By 1915, some 2,000 volunteers across North America were banding and watching birds. But the only thing the researchers could say for certain about the whistling swans was that they went south to Chesapeake Bay in the fall and north - somewhere - in the spring.
It would take half a century to solve this mystery.
But who wanted to know, and why? Curious scientists, for one, and farmers who wanted to keep their crops safe from hungry flocks of migrating birds. Later, airplane pilots needed to know. Flocks of birds - especially tundra swans weighing up to 20 pounds and with wingspans of up to six feet - can be dangerous to aircraft. The birds may hit the planes, damaging them, and even (on rare occasions) causing them to crash.
The swan that solved the puzzle
Finally, on an Alaskan summer day in 1970, pilot Jim King spotted a swan. He dipped a wing and set his float plane down on a lake. His passenger, scientist William Sladen, carefully checked the bird's coded neckband, and made a remarkable discovery. The seven-year-long project to find the spring-migration site of whistling swans was over. Dr. Sladen could tell, by the bird's neckband, that its name was Hope. Hope had been banded in the Chesapeake just six months earlier. She was the first banded swan ever sighted in Alaska! Alaska's North Slope was the northernmost summer nesting range for East Coast whistling swans.
Since that day, thousands more swans have been fitted with coded bands or radio transmitters. The swans are tracked along their 4,000-mile migration route by specially equipped airplanes and even by satellites. Today, traditional flight paths and stopovers have been mapped. (One of the biggest stopovers in the United States is the Devil's Lake Wildlife Refuge in North Dakota. Some 30,000 to 60,000 migrating swans stop off there about the second week in October.)
Migration routes are not precise. Sometimes storms blow a flock off course. In October 1971, police in Pittsburgh were alarmed by a loud, unfamiliar baying. It sounded like a riot! But it wasn't. Heavy clouds had forced a flock of 1,000 swans to land on the Allegheny River. The racket was just swans being swans.
Tundra swans usually fly several hundred miles a day on their migration flights. They fly about 18 to 30 miles per hour, though with a tailwind flocks have been clocked at 50 to 60 m.p.h.
They fly high, too: 6,000 to 8,000 feet. (Mallard ducks, though, have been spotted at 20,000 feet, and the migratory champion is the bar-headed goose, seen flying at 29,000 feet over the Himalayas.)
Like other migrating birds, swans fly in a slanted line or a "V" formation. The leader of the formation has the hardest job. He or she pushes through the air first. This makes flying easier for the birds following it. The birds take turns leading the flock. As one bird tires and drops back, another moves up to take its place.
With high-powered telescopes, scientists can identify a banded bird even if it's among thousands of others. Remember William Sladen, who found Hope in the Arctic? One of his early air chases in a plane includes this report: "One hour after the radio signal [from the birds], we were in the air and right over them. The swans and tracking plane played hopscotch over Ohio. The birds landed before dawn after flying nonstop for more than eight hours. The plane, only an imitation bird, had to land for refueling - a humbling thought!"
Poised for more discoveries
About 520 of the 650 bird species that nest in the United States (remember: tundra swans do not) fly south for the winter. They head south to avoid bad weather and find food. Some birds, like the tundra swan, migrate to the far north in the spring to nest. The 24-hour summer days near the Arctic Circle create an abundant source of food. The remoteness of the region also lends protection to their young. Safety and abundant food attract other birds and animals. Caribou also migrate north to bear their young.
By late September, the waterways up north begin to freeze over, and the swans and their offspring head south to milder climes.
Bird-banding solved the mystery of "Where do the swans go?" Today, researchers are poised to make more discoveries. Some 10 million North American birds now carry a metal leg band (in one of 14 sizes), neck tube, flag, or lightweight radio transmitter. Each one is numbered, and each number is entered in a master computer in Patuxent, Md.