Hundreds of trumpeter swans could die in the Island Park-Harriman State Park area this winter if an ambitious plan to relocate the rare birds fails, an expert says.

"Basically, there is not enough food (in the area) for any large number of birds to survive the winter," said Ruth Shea, an Idaho Department of Fish and Game regional biologist.With the prospects of losing a major portion of the Rocky Mountain trumpeter swan population, 13 government and private agencies have agreed to trap and move as many of the birds as possible this fall from Harriman to more suitable wintering areas in southern Idaho, Utah and Wyoming.

The project - the largest swan transplant ever - will begin in earnest in the next two weeks. Led by the U.S. Fish and Wildlife Service, an unusual array of government agencies is contributing to the program. In addition to Fish and Game departments from Idaho, Montana and Wyoming, the Canadian Wildlife Service and the Shoshone-Bannock Indian Tribes also will help.

"It's a high priority activity for us," said Chuck Peck, project coordinator for the U.S. Fish and Wildlife Service. "The potential for problems this winter is very serious."

Of the 2,000 trumpeter swans that winter in the greater Yellowstone ecosystem, 700 traditionally stay in the Harriman-Last Chance area. About 450 swans winter at the Red Rock Lakes Wildlife Refuge in southwestern Montana.

Most of the wintering trumpeters in the greater Yellowstone population migrate from western Canada. Shea said about 600 swans remain in the Yellowstone area year-round.

Both she and Peck agree the transplant program is essential because there is not enough food in Harriman State Park for the swans.

Shea said aquatic vegetation, the main staple of trumpeter swans, has been "stressed" by three years of low water flows. It also was heavily grazed last year by the 700 swans that wintered in the park, and summer growth has been "very poor," she said.

Ironically, the total number of trumpeters is growing because of Canadian and U.S. programs to re-establish the swan population.

"In a way we are a victim of our own success," said Carl Mitchell, assistant manager of the Red Rocks Lakes Wildlife Refuge.

Peck said the goal of the transplant program is to move about 500 birds. He estimated that there is enough food in the Harriman area to successfully winter about 100 swans.

The first phase of the plan is to safely trap as many of the birds as possible, Shea said. Eight to 10 people will start work on the process, and more will be used if necessary. Trapping methods will include shooting a net at the birds, swim-in traps, drive netting and using spotlights to blind the birds and catch them.

Once trapped, the swans will be marked and transported to other areas. Most will be released along the Snake River between the Fort Hall Bottoms and the Glenns Ferry area, but some also will be released in southwestern Wyoming and northern Utah.

If trapping is unsuccessful, officials will try to haze the birds and make them fly out of the area. That is a less attractive option than trapping because program officials will not be able to control where the swans go, or if they go at all.

Shea said if a large number of trumpeters remain in the area in January, a feeding program could be instituted. But it probably would be ineffective and increase the birds' susceptibility to disease.