Using population survey data of North American birds compiled since 1981, scientists at the Migratory Bird Center of the Smithsonian’s National Zoological Park in Washington, D.C., and the Wildlife Trust in New York have documented a significant population decline among several bird species following the introduction of the West Nile Virus in North America.

The affected species include some of America’s most familiar birds, including the American robin, American crow, blue jay, Eastern bluebird, house wren, tufted titmouse and black-capped chickadee.

Although it has long been been known that West Nile Virus—an introduced, invasive pathogen—does cause bird mortality, only recently have scientists been able to demonstrate the large-scale impact of the virus on the populations of a number of bird species.

“Our work demonstrates the broad and potentially devastating impacts that an invasive pathogen can have on our native wildlife,” says Shannon LaDeau, lead researcher of the survey and a Smithsonian postdoctoral fellow.

“Some species, like the American crow, showed population declines up to 45 percent regionally,” LaDeau continues. “It is also important to emphasize that we have only looked at a small subset of bird species in the United States. Most species, such as birds of prey and waterbirds, aren’t monitored at these scales, so we have no way of knowing how or if their populations are declining.”

Peter Marra, a National Zoo ornithologist and co-author of the survey study, emphasized that “with increasing globalization often come dire consequences for  native wildlife and their dependent ecosystems, including unprecedented movement of invasive pathogens around the world.

“The West Nile Virus serves as a clear example of how other pathogens, such as highly pathogenic avian influenza, might easily enter and affect our ecosystems,” Marra says. These results also emphasize the risks associated with global trade in wildlife. International wildlife trade, legal and illegal, is one of the primary ways pathogens move around the world. The United States and other countries in the Western Hemisphere should carefully consider banning future trade in wildlife, Marra says.