Tom Stehn, who oversees whooping crane conservation efforts for the U.S. Fish and Wildlife Service, says 21 percent of a flock of whooping cranes that migrates between northern Canada and the Aransas National Wildlife Refuge in Texas each year died off last year. Typically about 10 percent of the flock dies off.
Stehn says including new births, this year's flock is expected to drop by about 20 birds from last year's 270 when counted in the fall.
The whooping crane numbered just 15 in 1941 but now numbers 539 and is considered a success story by conservationists.