In the 1930s the snow-white, regal-necked trumpeter swan became the first symbol of endangered species preservation in America. In the succeeding years, the trumpeter made a strong comeback. But now one of the major remaining groups that winters in the Montana-Wyoming-Idaho area is experiencing mysterious problems.
There are four more trumpeters in the United States today than there were in 1931, when only 50 were counted. A core group in Yellowstone National Park escaped devastation by hunters, who sold the feathers and skin of the birds they killed.
Establishment of the Red Rock Lakes National Wildlife Refuge in Montana and transplantation of cygnets to Grand Teton National Park, Wyo., started the trumpeters on the road to recovery.
Then it was discovered that some 4,000 trumpeters, which breed in Alaska and winter on the Oregon coast, had been misidentified as whistler swans. This development eased concern about the birds' survival, and the plight of the swans slipped from public consciousness.
Gradually, the Rocky Mountain population built up until it was surveyed at 800 in 1968. At that time, the US Fish and Wildlife Service removed the trumpeter from its list of "rare species."
At about the same time, however, surveys began indicating that the trumpeter swans in this area were having mysterious problems. The overall population leveled off. The number of adults actually declined. Throughout the 1970s, winter surveys showed a gradual decline in the trumpeter population to a low of 550.
Concern over this trend prompted the Wildlife Service to conduct an intensive survey of the trumpeters last winter. At this time, 743 adults and 123 cygnets were counted, about the same as a decade ago.
This increase, rather than indicating renewed population growth, is partially due to the increased efforts on the part of surveyors, cautions US Forest Service biologist Ruth Shea. She has studied the trumpeter swans intensively and found the first clue to the problem.
The Rocky Mountain population of trumpeter swans remains at high risk because of its concentration. The birds winter in only two locations: Red Rock Lakes and Henry's Fork River near Last Chance, Idaho.
"This makes them extremely vulnerable," explains Miss Shea. She monitored the swans for three years as part of her master's thesis, studying 72 trumpeters' nests in the Yellowstone area from 1977 through 1979.
She found that only one-fourth of the cygnets made it from hatching to fledging. And of those that fledged, 15 percent appeared stunted or to be growing at an abnormally slow rate.
Despite these symptoms, autopsies of baby swans did not reveal anything unusual.
Meanwhile, the biologists sent egg shells to the University of Wyoming for testing. The results showed that all the shell samples were more radioactive than normal.
"This is the first thing we have that's out of line," says Miss Shea. "And no one is absolutely sure that the radioactivity is the cause of the high cygnet mortality or, if it is, where it is coming from."
Because the trumpeters are no longer on the endangered species list -- nor are they game animals -- the Fish and Wildlife Service has given them relatively low priority.
But now, because of this problem, government managers are paying more attention to these, the largest of swans and one of the oldest species of bird on earth.