Here in the Yukon, we mainly hear the good news about trumpeter swans. Once listed as endangered, their numbers have been slowly and steadily increasing.

But down south on their winter range the picture is not quite as rosy. In January and February of 2001, almost 200 carcasses of dead trumpeter swans were collected in the Sumas Prairie area near Abbotsford, B.C. and in neighbouring Whatcom County in Washington State.

Autopsies showed that the birds were poisoned by lead shot, and this is the second year in a row that a large number of dead swans have been found in the area. A die-off occurred in 1992 as well.

While biologists do not consider this level of mortality to be an immediate threat to the species, it could become a concern if the die-offs continue. And that means that biologists have to figure out where the birds are picking up the lead shot.

Washington State banned the use of lead shot for hunting waterfowl in the mid-1980s, and B.C banned its use in the Sumas Prairie area in the early 1990s. In 1999, a Canadian ban on lead shot for hunting most migratory game birds was extended from certain wetland areas to all of the country.

But lead shot can still be used for hunting upland game such as pheasants and for target shooting. Also, the old shot can hang around where birds can find it for a very long time.

Most of the birds -- 160 out of 198 -- were found in Whatcom County, Washington, which is where most of the birds roost at night. Wildlife officials are not sure whether the bids are picking up the lead at their roosting sites, or where they feed during the day.

Wildlife officials on both sides of the border are working on the problem. Laurie Wilson, a wildlife biologist with the Canadian Wildlife Service in Delta, says that they are trying several different approaches to find the sources of the lead.

They have been taking sediment cores at roost sites and in surrounding agricultural fields where the birds forage, concentrating on areas with a history of hunting. But swans can range far and wide when they feed, so they could be foraging in a wetland or other spot that has not been identified as a lead hot spot.

"The strange thing about these die-offs is that lead shot has been banned for the years, but we are not getting mortality every year, so we think that the climate and water levels might be playing some sort of a role," says Wilson.

The theory is that in dry years when water levels are low, the long-necked birds can pick up lead shot from sediments that they would not be able to reach when water levels are higher.

The CWS plans to start tracking some of the birds in the fall when they have just returned from their northern breeding areas, and should be relatively lead-free. After taking blood samples to check lead levels in some of the birds, they will radio-collar them and follow them closely to see where they are feeding.

"If any swans die from ingesting lead shot next year, then we would know if the source of lead is here or if they are not picking it up en route," says Wilson. "One bird had 196 pieces of shot in its gizzard, so there have to be some areas that are just loaded with shot."

Alternatives shots, made of steel and bismuth, do exist but they are more expensive than lead. Lead shot is not the only problem; lead sinkers and jigs are also toxic, and are particularly dangerous for diving birds like loons. Their use is banned in national parks and National Wildlife Areas, but not in other places.

The Canadian Wildlife Service estimates that about 250,000 waterfowl are killed every year by lead poisoning, and millions more are poisoned. Also the toxins are passed up through the food chain when scavenger such as eagles and coyotes feed on the poisoned birds.

Countries like Denmark and the Netherlands have banned the use of lead shot for all hunting, and some people think that it is time that North American followed suit.

Martha Jordan, a Washington board member of the Trumpeter Swan Society, has been dealing with the lead shot issue for longer than she would like to remember. "I look at this as an issue of toxic pollution," she says. "We need to ban lead, period. It is a toxin. We know this, and the alternative shots are there."

"When I look at the data on the toxicity of lead in the environment, it is staggering. Just look at the ramifications. There are 17,500 swans in the Pacific Coast population. So you have one percent of the population killed in one lead issue."

More information on lead shot and its effects can be found on the Canadian Wildlife Service website at http://www.cws-scf.ec.gc.ca/.