When the birds arrived at their wintering grounds in Florida's Chasshowitzka National Wildlife Refuge, volunteers put the younger cranes in enclosures to protect them from older birds in the area.
Older birds now make the migration on their own, Duff explained.
"The older generations come down, they harass the chicks, they take the food," he said.
Volunteers checked the birds on Thursday evening. Severe storms rolled in that night and early the next morning, making it impossible for the birds to be safely checked until Friday afternoon.
Initially the group believed all 18 cranes had died.
Yesterday workers picked up the signal of a radio transmitter worn by one of the juvenile cranes. A team of trackers found the young crane with a pair of sandhill cranes in a nearby area with good habitat.
Flooding or a lightning strike may have killed the rest of the birds, Duff said. The group is awaiting necrology reports to confirm the cause of death.
A Successful Journey
Duff called last year's journey the most successful of Operation Migration's six years, with the team taking 18 cranes from Wisconsin to Florida without one injury, illness, or loss among the birds.
The journey from Necedah National Wildlife Refuge in Wisconsin to Chasshowitzka National Wildlife Refuge took 76 days, making it the longest migration in six years. Poor flying conditions kept both cranes and ultralights grounded for several days at many of the stopovers.
(Watch video: "Cranes, Planes Take off on 2006 Winged Migration" [October 6, 2006].)
Along the way, crane supporters turned out at several flyovers, including a December 19 flyover at Florida's Dunnellon/Marion County Airport—the last leg of the migration—that drew hundreds of observers.
Genetic Diversity Lost
Many of the cranes released during the project's early years were the offspring of only a handful of parents.
The Class of 2006 had greater genetic diversity, which would have broadened the flock's breeding stock had they lived to reach breeding age.
"That was all lost," Duff said, before the lone crane was found alive.
While little is known about the birds that have flown with Operation Migration during past years, there's still reason for hope.
One critical group of cranes is safe, workers say.
In 2006 a pair of cranes that learned to migrate in 2002 hatched a wild-born chick, the first in the eastern population in more than a century.
The crane family reached Florida on December 9, indicating that the migration route can be passed on from generation to generation in the wild.
Last week this family remained in an inland marsh area, protected by trees, and weathered the storm, Duff said.
While the cranes' loss represents a blow to the program and its future funding, as well as to the crane population, efforts to re-establish this population will continue, Duff said.
"We have to progress," Duff said, "and I think everyone is just more determined to plow ahead."
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