SUMAS, Wash. (AP) -- Years of collecting dead carcasses and examining lead-poisoned livers have convinced Mike Smith of this: to save Pacific Coast trumpeter swans, he has to haze them.
As the sun set behind Judson Lake - the likely source of the lead poisoning - the wildlife biologist kept vigil in a cramped watchtower with a night-vision scope, a noisemaker and a laser.
His mission is to scare the swans off the lake, away from the shotgun pellets that litter the lake bottom and have killed hundreds of the birds.
It wasn't long before Smith heard a distinctive swan honk and then spotted a snow-white bird gracefully land on the water. Smith fired his noisemaker, sending a red flare whistling into the sky. The swan didn't budge. He fired again. This time the bird flew away.
"It is bird harassment for a few moments of their life, but it certainly seems to extend their life," Smith said.
When trumpeter swans started dying by the hundreds in recent years, scientists traced the problem to this shallow 100-acre lake that straddles the U.S.-Canadian border.
Lead shots have been banned for waterfowl hunting since 1991. But wildlife scientists believe the swans were swallowing leftover pellets from the muddy bottoms of lakes and wetlands.
The lead enters the birds' bloodstream and paralyzes their internal organs, Smith said. They die within weeks.
"All indications are that this is a major source," Smith said of Judson Lake. "We know there's lead here. Since we've kept them off, the mortality has gone way down."
About 100 swans died of lead poisoning in each of those years, a 50 percent drop from the five-year average before hazing. About 1,600 swans have died of lead poisoning in the region since 1999.
The swans, North America's largest waterfowl, usually arrive in northwestern Washington and southwestern British Columbia in early November. One-sixth of the world's population spends the winter in the Pacific Northwest before migrating to central Alaska in April.
Native trumpeter swans have made a comeback in recent decades. About 8,000 swans were counted in the area, compared with about 100 in the early 1970s, according to the state department of fish and wildlife.
It takes only one or two pieces of shot to kill a swan, Smith said. Most of the birds that scientists tested had ingested an average of 20 whole pellets, he said.
"When you see one up close ... and get some idea of just how big and beautiful they are and then to go and see them succumb to as horrible a death as lead poisoning, it's quite heart-wrenching," Smith said.
In 2001, scientists with the University of Washington, Washington Department of Fish and Wildlife, U.S. Fish and Wildlife Service, Canadian Wildlife Service and Trumpeter Swan Society trapped and radio-collared about 300 swans to trace the source of lead.
They collected dead carcasses, took blood samples and tracked the birds' patterns. They also took hundreds of core samples from their forage and roost sites and found high lead density in areas that swans frequently used, including Judson.
"We feel really good about Judson Lake and what we've been doing there," said Jennifer Bohannon, a biologist with the state Department of Fish and Wildlife.
But "we need to come up with a long-term solution," she said. "I don't think hazing year to year is the answer. That's the challenge that lies ahead."
Local, federal, Canadian fish and wildlife officials and others are now trying to come up with a cleanup plan.
While swan hazing has led to an overall drop in deaths in the area, scientists discovered unexpected deaths last year in two counties, Skagit and Snohomish, north of Seattle.
It's unclear whether the swans pick up lead in the north and fly south to die, or have found new sources of lead. Scientists are starting to monitor other lakes.
"We went to nontoxic shot in 1991 and how many years later we're still losing these animals to lead shot," Jordan said. "You've got to know there are more lead from other sources."
She noted that lead shot is still legal for hunting upland birds such as pheasant or quail, and for skeet or trap shooting.
Smith and two other university colleagues will haze Judson Lake until January, when the water level is too deep for the swans to reach the lake bottom.
Smith usually hears the bugle-like honks before he sees them from his makeshift 6-by-6 foot tower. The swans try to roost on the lake at night, after foraging on corn stubble and winter wheat crops in nearby farms.
If the noisemaker doesn't work, Smith shines a red laser at the birds to scare them away. As a last resort, he gets into an airboat to physically chase them away. Starting up the roaring engine is usually enough to do the trick.
Within several hours, Smith recorded a total of 34 swans hazed from the lake.
"You learn patience," he said. "It's like fishing for birds."
On the Net:
University of Washington: http://depts.washington.edu/wacfwru/index.shtml
Washington Department of Fish and Wildlife: http://wdfw.wa.gov
Trumpeter Swan Society: http://www.trumpeterswansociety.org