A fungal disease is being blamed for the deaths of trumpeter swans spending the winter on Whatcom County's Wiser Lake.
Martha Jordan, wildlife biologist and chairwoman of Washington Swan Stewards, said the big white birds have been congregating on the lake by the thousands this winter. The birds prefer to spend the night afloat in the lake closest to their food supply, and this year, that appears to mean Wiser Lake.
Because of concern about swans dying from ingestion of lead shot deposited by hunting in and around local lakes, researchers have been keeping a close eye on swan populations in northwest Washington.
Jordan said 149 dead swans have been found in Whatcom County alone between Jan. 27, 2014, and the migratory birds' arrival in the area earlier in the winter. During the same period last year, fewer than 100 had been collected in the entire northwest Washington area.
"Whatcom County is off the charts for us this year," Jordan said.
Chris Danilson, district wildlife biologist in the Washington Department of Fish and Wildlife's La Conner office, said some of the dead swans have been sent to the U.S. Geological Survey's National Wildlife Health Center in Madison, Wis., for analysis. That analysis showed that lead poisoning is still killing some birds, but the lead death toll appears to be dropping thanks to efforts to shoo birds off heavily contaminated Judson Lake, which straddles the U.S.-Canada border just west of Sumas.
Fungus, not lead, appears to be the big killer this year. Danilson said some of the dead birds were infected with aspergillosis, a fungal disease that birds can contract from eating moldy grain in fields and farm yards.
Danilson doesn't think the upswing in aspergillosis is evidence of any other serious environmental problems afflicting the swan population. He noted that the swan population continues to rise, and now stands at about 14,000 in the northwest part of the state.
Aspergillosis outbreaks just seem to happen now and then in waterfowl populations, according to Danilson and online information on the National Wildlife Health Center's website. Danilson said a similar outbreak killed several hundred ducks in the region a few years ago.
Jordan said the change in agricultural use in northern Whatcom County has been dramatic in recent years. Fields in the Sumas area once used for dairy pastures or corn silage have been converted to raspberries and blueberries, which provide no food for wintering waterfowl. As a result, swans are doing more foraging to the west and south, making Wiser Lake a more popular overnight spot.
"All of that is really a loss of habitat for wildlife," Jordan said. "Where do we go from here? How do we support the birds?"
But she added, "Farming is better than a development."
Trumpeter swans have been wiped out of much of the eastern portion of their former North American range, because of both habitat loss and many years of heavy hunting for feathers as ornament and for quill pens. But in recent decades, with the birds no longer hunted, their population has been growing.