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TRUMPETER SWANS - Preservationambience, Trumpeter SwansWe're listening to the sounds of Trumpeter Swans. Although they once inhabited virtually all of North America, today they exist in only a few isolated regions. I'm Jim Metzner and this is the Pulse of the Planet.If Trumpeter Swans continue to inhabit just a few areas, they run the risk of having their entire population wiped out by disease or harsh weather. So, in places like Henry's Fork River near Yellowstone National Park, concerned scientists are trying different methods of redistributing the birds.Shea: And the most successful method has been night-lighting, where the crews go out on the Henry's Fork River in a small air boat, come up quickly on a group of swans with a bright light. They become blinded, they can't see the horizon, they can't take off, and then as the driver maneuvers the boat toward the birds, the man in front reaches out with a salmon fishing net and captures a swan.Ruth Shea is a biologist with the Idaho Department of Fish and Wildlife.Shea: In the winter of 1991, we moved 353 swans. I've been monitoring those marked birds and we're very happy to see that somewhere between 15 to 20% of those swans have returned to those release sites, those target wintering areas and put to use the knowledge that they acquired the year before. The program won't be a success, however, until adequate numbers of these birds go back north, nest successfully, raise young, and then lead those young to the new wintering grounds. It's like rebuilding a web. The web had been reduced down to one strand and now we're adding a multitude of strands to it. And hopefully, it'll be a much stronger fabric when we're done.This archival program is part of our thirtieth anniversary celebration.