West Nile killing off beloved US birds - study

CHICAGO, May 18 (Reuters) The West Nile Virus is taking a worse-than-expected toll on some favorite birds in North America such as robins and chickadees, US researchers said.

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 per cent 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 yesterday, whose work appears in journal Nature this week.

''When West Nile first showed up in '99, people knew that crows 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.

The researchers also found a correlation between the prevalence of the disease in birds and human infections.

''The birds are indicating what the intensity of the epidemic is that year,'' he said.

The seven hardest-hit species are all associated with cities and suburban areas, suggesting that people are creating breeding places for mosquitoes.

''We're providing the larval habitat for those mosquitoes,'' Kilpatrick said, noting the mosquito's affinity for breeding in stagnant, polluted water like that found in bird baths and catch basins.

Between 1999 and 2006, nearly 24,000 people were reported infected with West Nile virus in the United States, with 962 deaths, according to the US Centers for Disease Control and Prevention.

The virus is also common in Africa, southern Europe and the Middle East.

Most people who are infected with the virus, about 80 percent, show no symptoms.

But about one in 150 people infected with West Nile Virus will develop severe illness, with symptoms including high fever, disorientation, coma, tremors, convulsions, vision loss and paralysis, according to the CDC.

REUTERS RN HS0851