"When a whooping crane stands up, you notice. At 5 feet in height, it's America's tallest bird. Its wingspan is more than 7 feet, its body snowy white, its wingtips jet black.
By the 1940s, the birds had nearly gone extinct. Biologists have worked hard to bring them back, by breeding whoopers in captivity and releasing them in the wild. There are now several small wild populations in the U.S.
Perhaps the most remarkable is the eastern group. For 15 years, biologists have been teaching some of the young cranes to migrate between Wisconsin and Florida by leading them with an ultralight, one-person aircraft.
Now, however, biologists have discovered that teaching the cranes to migrate seems to have created serious problems for the birds — they rarely reproduce successfully. The Federal Fish & Wildlife Service has halted the flights and is now trying to figure out what went wrong."