West Nile Devastated U.S. Bird Species

May 16, 2007

West Nile virus or a similar disease could wipe out many of the U.S.'s backyard birds, profoundly changing some of the country's most familiar wildlife and ecosystems.

That's the finding of a new analysis of 26 years of data from the national Breeding Bird Survey—data that reveal the dramatic effects of the 1999 arrival of West Nile virus in the U.S.

Lead author Shannon LaDeau of the Smithsonian Migratory Bird Center and her colleagues found that species that thrive near humans suffered extremely high death rates from the disease.

Up to 45 percent of crows died after the virus arrived, with robins, chickadees, and eastern bluebirds not far behind.

Some of these populations had been increasing before the virus hit, which is a good indication that West Nile caused the declines, the authors write.

The disease may not completely wipe out bird populations on its own, the scientists add, but it is an alarming addition to existing population threats such as climate change and habitat loss.

"They're our backyard species, and we haven't been watching them as much as we're watching the other species, because people consider them safe," LaDeau told National Geographic News.

The study appears in this week's issue of the journal Nature.

Mosquito, Bird Link

Since West Nile Virus began its mosquito-borne spread across the U.S., the Centers for Disease Control and Prevention has logged more than 12,000 human West Nile cases and 960 deaths.

Spikes in bird deaths among some species—including crows, house wrens, and eastern bluebirds—were linked with numbers of human cases, which peaked in 2002 and 2003, the study found.

That's because mosquitoes that carry West Nile fare best around people, where sources of stagnant water used for breeding—including sewers, old tires, and forgotten watering cans—abound, LaDeau said.

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