Searching For Sources of Lead Poisoning in Swans
Doug Williams

While it has been banned in the United States for more than a decade, the toxic legacy of lead birdshot continues to take a grim toll on visiting northern trumpeter and tundra swans in Skagit and Whatcom counties. "Research has shown that from the day a swan picks up lead shot, it will take about three weeks for that bird to die," said Mike Davison, WDFW wildlife biologist who is spearheading the Department's efforts to end the poisoning of swans.

The winter of 2001-02 was the deadliest on record, with an estimated 247 swans - 95 percent of them trumpeters - dying from lead poisoning in the two counties and adjacent portions of British Columbia. About 4,000 swans over-winter in Skagit County, with another 1,000 or so in Whatcom County.

The birds aren't being shot. Instead, the long-necked swans are ingesting spent lead shot that has settled onto the bottom of shallow lakes and ponds where the birds feed. The lead shot ends up in the bird's gizzard where the soft metal is ground up and slowly leaches into the swan's bloodstream.

The Department has teamed with Canadian fish and wildlife biologists, the U.S. Fish and Wildlife Service, the Trumpeter Swan Society, the Bellingham Chapter of the Audubon Society, and the Pilchuck Valley Rehabilitation Clinic to identify the places where swans are ingesting spent lead shot, and finding ways of removing the poisonous material from the environment.

The main thrust of the work has been to collect more data on the birds' movements. A total of 26 swans - 19 in Whatcom County, plus seven in British Columbia - have been fitted with radio-transmitting collars that allow biologists and volunteers to track the birds' movements throughout the region, and possibly pinpoint the places where they're picking up spent shot.

Davison said the 26 collared birds were tracked to 50 different sites. Two of the collared birds died from lead poisoning, and their deaths led the biologists and volunteers to focus in on about 12 specific locations. The team has done preliminary core sampling at some of the sites of interest, and early analysis is beginning to reveal lead shot sources, Davison said.

"Based on our early analysis, there appears to be a window of time when the birds are becoming exposed to the lead shot, so we'll focus our future research on the locations that the birds are visiting earlier during the time frame that they're in the area," he said. "Our goal for this coming winter is to try to get more collars on birds earlier in the season."

Davison said an intensive sampling effort of suspected lead-poisoning sites is outside WDFW's ability, given current budget and staffing levels. "We're looking to take the lead on all of the research work, while another agency or group could come in and facilitate the more-intensive core sampling effort," he said.

Non-toxic shot requirements were phased in over time, beginning in 1986, and ending in 1991 throughout the United States. Non-toxic shot has been required for all waterfowl hunting in Canada since 1999 but has been required in parts of BC for almost 10 years. Non-toxic shot is also required for public hunting areas that are used for both pheasant and waterfowl hunting, and includes all of the pheasant release sites in northern Puget Sound. Hunters are encouraged to convert to non-toxic shot for all upland bird hunting.

Lead-poisoned swans pose a health threat to other wildlife, including bald eagles, which feed on swan carcasses and can get secondary lead poisoning. Davison said two dead eagles found this year in the area are being tested for lead poisoning. "Potential secondary mortalities point out the importance of collecting sick or dead swans as soon as possible," Davison said. "The value of the rescue and recovery work that our partners do is immense."