Leaden swan song

From Montreal, at a meeting of the Society of Environmental Toxicology and Chemistry

Since 1999, more than 2,100 trumpeter swans in northwest Washington and southwest British Columbia have died—about 15 percent of the birds that winter in this region. Nearly 80 percent of the deaths occurred because the birds ate lead shotgun pellets, reports a U.S.–Canadian team of researchers.

Some 25,000 trumpeter swans breed in this region and other North American areas along the Pacific, notes team member Laurie Wilson, a wildlife biologist with Environment Canada in Delta, British Columbia. Over the past several decades, these swans have been climbing back from the brink of extinction, so the high death rate from lead poisoning is especially troubling.

To date, the team has autopsied more than 1,700 carcasses. “We’re recovering, on average, 22 lead pellets” per bird, says Wilson. However, she adds, more than 4 percent of the birds had gizzards containing at least 100 pellets; a few had 600 or more there.

Blood samples collected from 250 birds migrating to the region showed that the birds flew in carrying low amounts of lead. That suggests that the area contains lead hotspots that are poisoning foraging birds, say Wilson and her colleagues.

Although lead shot has been banned from waterfowl hunting in this region for more than a decade, the researchers have identified several foraging sites where old lead pellets are still abundant in soil.

“These birds need grit for digestion,” Wilson notes, “and the shot sizes we’re finding in them are very similar to other grit that these birds select.” If wildlife ecologists can identify more lead-shot hotspots, she says, the next goal will be to remove or bury the toxic shot in those locations.