Birds that once flourished in suburban skies, including robins, bluebirds and crows, have been devastated by West Nile virus, a study found. Populations of seven species have had dramatic declines across the continent since West Nile emerged in the United States in 1999, according to a first-of-its-kind study. 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. In some places, such as Maryland, crow loss was at 45 percent, and around Baltimore and Washington, 90 percent was gone.