West Nile virus is killing many of America's favorite backyard warblers, along with crows, blue jays and other birds. The virus is the most important mosquito-borne illness reported in years. Although it primarily affects birds, it affects people too. Transmission of the disease in North America has resulted in an estimated 280,000 illnesses, over 26,000 reported cases and 996 human deaths.

Scientists at the Consortium for Conservation Medicine (CCM), based at Wildlife Trust, New York and the Smithsonian Institution's Migratory Bird Center found that many species of birds enjoyed by birders, including backyard favorites such as tufted titmice and chickadees are suffering significant declines in population because of the West Nile Virus.

Although none of the 20 bird species has gone extinct from the virus, it has reduced the population of American crows by about 50 percent in some regions so far.

In a report published Thursday in the journal Nature, the group said that along with tufted titmice and chickadees, American robins, Carolina and black-capped chickadees, blue jays, American crows, eastern bluebirds, and house wrens were being infected and killed with the virus.<

The group said that the spreading disease could make many varieties of once common backyard birds "uncommon,"

In addition, Dr. David Gibbons, Head of Conservation Science, Royal Society for the Protection of Birds, said, "Globalization is likely to spread infectious diseases further and faster, which can only add to the deleterious pressures already facing birds and other wildlife, such as climate change, habitat loss and introduced predators."