BALTIMORE (AP) _ Trumpeter swans vanished from the Chesapeake Bay nearly 200 years ago, their robust calls of ``ko-ho'' silenced by demand for quill pens, powder puffs and plumes for ladies' hats. Today they returned.

Scientists trying to restore America's largest waterfowl to the mid-Atlantic by re-teaching the majestic birds to migrate have their hopes riding on five young birds that have been tricked into thinking that a bright yellow ultralight plane with an overarching white wing is their parent.

The young trumpeter swans will spend the winter at a 255-acre farm on Maryland's Eastern Shore, where the three females birds arrived this morning after following the motorized hang glider 110 miles from the Environmental Studies at Airlie Center in Warrenton, Va. The two males will set out later.

``It was thrilling to see the swans fly into the farm for the landing because it was the culmination of a journey for all involved in the experiment and for the birds,'' said Bob Ferris, the owner of Lack Cove Farm and head of the restoration project.

On Thursday, the three females and the ultralight took off at 7:50 a.m. from a cornfield close to the Airlie Center and flew 65 miles with a rest stop. They finished the journey this morning.

Trumpeter swans ``are certainly most difficult, most individualistic,'' said Dr. William J.L. Sladen, the Airlie Center's director.

In 1989, Sladen teamed up with ultralight enthusiast William Lishman to teach the more compliant Canada geese to migrate. In 1993, they completed the first ultralight-led goose migration from Ontario, Canada, to the Airlie Center, a trip depicted in the 1996 movie ``Fly Away Home.''

As recently as October, an ultralight painted to look like a whooping crane guided three of the endangered white birds and six sandhill cranes on a nine-day, 800-mile trip from Idaho to a wildlife refuge in New Mexico.

The goal of this latest project is to re-establish a migration route between upstate New York and the Eastern Shore. Migration is considered important, because birds that don't fly south for the winter are more likely to exhaust their food supply, become a nuisance to people, get sick or freeze to death.

Trumpeter swans learn to migrate from their parents. But if the older birds in a flock are killed by hunters, the young don't know where to migrate and the knowledge is forever lost.

``We started training them before they came out of the egg,'' said Bob Ferris, director of species conservation for Defenders of Wildlife, a Washington-based group that has devoted $175,000 to the nearly $1 million project. ``We played a recording of an ultralight engine so they would get used to it.''

The group is hoping to raise the rest of the money from contributions.

Seven birds hatched at Airlie in late spring. Three females and two males were chosen for the mission.

To get the birds used to the ultralight, researchers carried tape recordings of the plane's engine noise. The baby birds followed the sound.

In late July, they were exposed to the real thing. When the plane rolled, they followed it. By mid-September, the birds were ready to start flying. When the ultralight rose into the air, the birds followed.

The next step was to train them to fly to the Defenders-staffed farm near Crapo, Md., as a flock _ more of a challenge than scientists expected. Trumpeter swans are more stubborn and unpredictable than Canada geese.

``The females were flying pretty well together, and when we mixed the males in there were some problems,'' Ferris said. ``They will fly a couple of miles in some direction and then one of the males says `I'm going to go back and sit on the pond,' and they'll peel off and the others birds will follow.''

Trumpeter swans once inhabited nearly all of North America. About 100,000 wintered in the Chesapeake Bay area about 200 years ago, but by 1932 overhunting had left only 69 in the lower 48 states.

Trumpeter swans once inhabited nearly all of North America. About 100,000 wintered in the Chesapeake Bay area about 200 years ago, but by 1932 overhunting had left only 69 in the lower 48 states.

There now are about 19,000 trumpeter swans in North America, 16,000 of them in a migratory flock that breeds in Alaska and winters in the Pacific Northwest. A group of about 2,500 breeds in Canada and winters in Idaho, Wyoming and Montana. And the remainder are in a few small, non-migratory flocks in Iowa and around the Great Lakes.

The birds, white with a black beak, weigh up to 30 pounds, have an 8-foot wing span and can stand 6 feet tall with neck outstretched. They have a long, convoluted trachea that produces the resonant trumpeting sound.