Bird Species Plummeted After West Nile

The analysis did not seek to document every affected species, focusing instead on just 20 for which annual data were available going back many years. The data came from the North American Breeding Bird Survey, conducted by volunteer bird-watchers at the same 19,000 locations every year.

Because the survey is largely a record of bird calls heard on certain rural roads during morning outings that take place each June, the new analysis does not capture the fates of waterfowl, nocturnal birds and birds other than songbirds, including the hawks and owls that are believed to be among the hardest-hit species.

"The declines we see are probably a signal of a more serious ecosystem challenge that is having much broader effects than we're currently able to detect," LaDeau said.

Given the interconnectedness of the food web, those broadened effects are almost certainly reaching beyond birds, she added.

For example, crows are important scavengers, clearing away roadkill and keeping competing pests at bay. And their penchant for eating other birds' young suppresses a wide range of other avian species.

"American crows are often considered a nuisance, but when the crows go, do we get more rats?" LaDeau asked. "What other scavengers come in, and what happens to the bird populations that are regulated in part by crows?"

Field studies suggest that the loss of seed-eating birds such as chickadees could also have ecological ripple effects by reducing the natural dispersal of seeds.

Also of concern: bird species that are weakened but not devastated by West Nile could collapse if a second challenge arises, such as an especially hot or dry summer or the loss of a crucial food source due to disease or pollution.

Beyond working to limit the unregulated transport of animals, the best thing people can do to stem West Nile's tide of destruction is to keep their yards clear of standing water, Marra and LaDeau said.

Even a bottle cap of water can be home to hundreds of mosquito larvae, LaDeau said -- a chastening thought for backyard beer drinkers.