West Nile killing off beloved U.S. birds: study

By Julie Steenhuysen

CHICAGO (Reuters) - The West Nile Virus is taking a worse-than-expected toll on some favorite birds in North America such as robins and chickadees, U.S. researchers said on Thursday.

They studied 20 North American birds and found declines in seven species from four families as a result of the virus, which lives in birds and other animals and can be transmitted by mosquitoes to humans.

The impact was especially strong among the American crow population, which has been cut by 45 percent since West Nile first appeared in the United States in 1999.

"Seven out of 20 is a substantial number," said A. Marm Kilpatrick, senior research scientist for the Consortium for Conservation Medicine at the Wildlife Trust, whose work appears in journal Nature this week.

"When West Nile first showed up in '99, people knew that crows were dying and jays were dying, but no one knew if there were any population level impacts," Kilpatrick said in a telephone interview.

Kilpatrick and colleagues analyzed 26 years of survey data on 20 bird species to evaluate the impact of West Nile. Besides the American crow, robin, Carolina and black-capped chickadee, and blue jay, other significantly impacted birds were tufted titmice, eastern bluebirds and house wrens.

Only two of the seven species -- blue jays and house wrens -- had recovered to pre-West Nile Virus levels by 2005.

"What our study also suggests is there are other species that are impacted," Kilpatrick said.