A ninth crane separated from the flock had to be retrieved by truck to join the others. Each bird carries a radio transmitter.

"They don't like to be alone, so maybe this experience will make him join closer to the flock," Guilfoyle said.

The full-grown but juvenile birds, hatched five months ago at a government farm in Maryland, are part of a carefully planned experiment to teach essentially wild birds how to migrate.

The whooping cranes, like a flock of sandhill cranes before them, have been trained to follow in the slipstream of ultra-light aircraft piloted by people disguised in bird-like suits. The suited handlers are careful never to speak in the birds' presence, or show skin, so that the normally cautious creatures do not grow accustomed to human contact.

Last year's test of the technique with sandhill cranes was successful when the birds returned on their own this spring to the Wisconsin preserve from their Florida wintering grounds.

The only other migratory flock of whooping cranes, which were decimated in the past century by hunters and the draining of their preferred swampy habitat, spends winters on Texas' Gulf Coast and summers in Canada. Scientists say that flock is vulnerable to hurricanes or oil spills.

In the 1940s the population of whooping cranes fell to just 15 birds, but they now number about 400. One flock lives year-round in Florida, and a private group called "Operation Migration" has received government aid to reestablish a migratory flock east of the Mississippi River.