That success has been repeated in many areas, due largely to a relatively abundant supply of eggs in Alaska. But transporting those eggs back to the "Lower 48" is a challenging feat indeed.
The eggs are collected when the embryos are 20 to 25 days old, Johnson says, because they are hardy enough to survive the rigors of transcontinental travel.
"We had special boxes that held the eggs in an upright position so the little embryos didn't get scrambled," Johnson says. The boxes were packed with hot water bottles and loaded aboard commercial aircraft for the 18-hour trip from Fairbanks to points south.
Johnson says his group has collected 869 eggs over the past few years, and 777 of them hatched. Of those, 661 survived, and 584 were released into the wilds.
"That's right around 90 percent success" at each step in the process, he says.
Some of the birds were held back for genetic testing, and that revealed the importance of collecting the eggs in Alaska. It turns out that the Alaskan swans have far greater genetic diversity than their cousins to the south, thus increasing their odds of survival.
But like many other species, trumpeter swans have to be taught some of the keys to survival. Not everything comes naturally.
Trumpeters need to move south for winter foraging, and without parents around to show them the way, some scientists have thought the transplants would surely perish. That has led some to take exotic measures, including sending ultra-light aircraft along with the flock to guide them to greener pastures.
But as it turned out, most swans that have been reared and released in the Great Lakes have managed to survive without traveling south.
"We thought migration was a prerequisite to the successful restoration of trumpeter swans to the Great Lakes region," Johnson says. "But we estimate that fewer than 20 percent are migrating into southern Illinois and Missouri" for the winter.
"What we didn't know is how adaptable these birds are," he adds. If their preferred aquatic plants aren't available in the winter, they just hop into the farming fields and feed on "waste grain," he adds.
Success Despite Hazards
However, the danger is far from over. Some trumpeters may fall victim to the good intentions of people who set out food for them, tempting them to hang around instead of heading south for more nutritious winter habitats. The birds are particularly susceptible to lead poisoning, and there's a lot of lead buckshot in the bottom of their feeding areas. They also tend to fly low, even in areas of high tension wires.
And although protected by law, there is the constant danger of a hunter mistaking the trumpeter for a game bird, or the vandal doing what vandals do best.
The statistics, however, are encouraging.
"The population is increasing at close to 25 percent per year," Johnson says. Of course, some of that increase is from the continued reintroduction of chicks from eggs collected in Alaska, but the mature birds are also reproducing.
"We're still putting a couple of hundred birds a year out, but we're producing 600 wild birds a year, and that's pretty impressive," he says.
Equally significant is the fact that the birth rates exceed the death rates, meaning the population is growing even without the introduction of new birds.
So listen, and perhaps you will hear the haunting sound of the trumpeter, playing a tune that hasn't been heard in some parts for more than a century.
Lee Dye’s column appears weekly on ABCNEWS.com. A former science writer for the Los Angeles Times, he now lives in Juneau, Alaska.