Five trumpeter swans found dead in January in the Dungeness Valley near Sequim (skwim) were all poisoned by lead shotgun pellets they ingested.
A veterinarian with the state Fish and Wildlife Department, Kristin Mansfield, told the Peninsula Daily News the birds' livers contained lethal levels of lead.
The swans pick up the pellets while feeding. They consume grit to help break up food in their gizzards.
Lead shot has been outlawed for hunting since 1991, but remaining pellets have killed hundreds of the federally protected swans in recent years, mostly on wintering grounds in northwestern Washington and southwestern British Columbia.