Bird populations suffer; regional increase expected

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Drastic population declines among several common species of North American birds have been recorded since the arrival of the West Nile virus in 1999. Some of those trends are beginning to be seen in the region and may become more apparent in Washington state in the future, according to a WSU scientist.

In a nationwide study, including 20 species, American crows were the hardest hit, declining about 45 percent overall from 1998 to 2005. Also dropping are populations of American robins, chickadees, eastern bluebirds, blue jays, tufted titmice and house wrens.

Data for the study came from a North American Breeding Bird survey, which is conducted by volunteer bird watchers annually at the same 19,000 locations. The results were analyzed by the National Zoo.

The West Nile virus is native to Uganda and is believed to have been transported to New York inside a bird or mosquito in 1999, probably on a plane or ship. Since then, it has spread rapidly, one mosquito bite at a time, leaving a sizeable but unknown number of birds dead in its wake — along with thousands of horses and, to date, 962 people.

Washington remains relatively unaffected by the virus with only 13 recorded bird cases and three human cases in 2006.
Dan Bradway, laboratory manager for the Washington Animal Disease Diagnostic Laboratory at Washington State University in Pullman, said some common bird species are just impacted more severely by West Nile.

WADDL conducts tests on suspected birds in an effort to track both the West Nile virus, and the avian or bird flu virus, known more properly as the Eurasian lineage strain of H5N1 influenza A.

Scientists worldwide are attempting to monitor the avian flu and share that information. Through mutations, the avian flu poses a potential threat of causing a pandemic. Currently, though, it is not easily transmittable between humans.

“The (West Nile) virus amplifies itself in crows, jays and magpies,” Bradway said. These birds belong to the corvidae family which carry a heavier load of the virus, he said.

Five horses in Yakima County also contracted the virus in 2006, Bradway said. Horses while not highly contagious when infected, are very susceptible to the virus, he said. Vaccines for horses are available, he said.  

Aanalysis of the national bird survey did not seek to document every effected species, focusing instead on just 20 for which annual data were available going back many years. 

Washington and North Idaho can expect a higher impact from the virus in 2007 though, Bradway said. However, it is too early in the season to know just how much, he said.

An up-to-date map of the migration of the West Nile Virus and case numbers can be accessed at

For more information on WSU’s work to monitor the West Nile virus and avian flu, go ONLINE @

Note: This article is a composite of a WSU Today interview with university staff and information from other media stories including “West Nile taking toll on birds,” at the Seattle Times,

For related article, go to:

* Tacoma News Tribune — Preventive measures aim to stop West Nile,