Washington – Birds that once flourished in suburban skies, including robins, bluebirds and crows, have been devastated by West Nile virus, a new study has found.
Populations of seven species have had dramatic declines across the continent since West Nile emerged in the U.S. in 1999, according to a first-of-its-kind study. The research, to be published today in the journal Nature, compared 26 years of bird breeding surveys to quantify what was known anecdotally.
“We’re seeing a serious impact,” said study co-author Marm Kilpatrick, a senior research scientist at New York’s Consortium of Conservation Medicine.
West Nile virus, which is spread by mosquito bites, has infected 23,974 people in confirmed cases since 1999, killing 962, according to the Centers for Disease Control and Prevention.
But the disease, primarily an avian virus, has been far deadlier for birds. The death toll for crows and jays is easily in the hundreds of thousands, based on the number dead birds found and extrapolated for what wasn’t reported, Kilpatrick said.
It hit the seven species – American crow, blue jay, tufted titmouse, American robin, house wren, chickadee and Eastern bluebird – hard enough to be scientifically significant. Only the blue jay and house wren bounced back, in 2005.
The hardest-hit species has been the American crow. Nationwide, about one-third of crows have been killed by West Nile, said study lead author Shannon LaDeau, a research scientist at the Smithsonian Migratory Bird Center in Washington. The species was on the rise until 1999.
Colorado’s American crows fared slightly better than their eastern cousins, as did crows in Oregon, although crow populations in both states dipped.
West Nile invaded Colorado in 2002 and Oregon in 2004, after first appearing in New York in 1999. Researchers noted the die- offs came in patches, with many in some places and none in others. Maryland appeared to be the epicenter of bird deaths, though that was partly because the data from New York were not as good, LaDeau said.
Maryland’s chickadees, Eastern bluebirds and robins were 68 percent, 52 percent and 32 percent below expected levels in 2005.
“That heavily packed urban corridor is a bad place to be a bird,” LaDeau said. “The reason for that is that the mosquito prefers human landscape. They do very well in suburbia.”
Denver Post staff writer Katy Human contributed to this report.
