Posted on Fri, Jul. 09, 2004
LOS ANGELES - As West Nile virus spreads across California, bird watchers worry that the mosquito-borne infection could kill thousands of the region's birds and potentially devastate sensitive species.
Within San Bernardino, Los Angeles and Riverside counties, the virus has killed an estimated 660 crows and at least 26 other birds, including ravens, Western scrub jays, sparrows, mockingbirds, red-tailed hawks and mallard ducks.
The numbers are based on bird carcasses tested at the California Animal Health and Food Safety Lab in Davis, but officials estimate far more birds have succumbed to the virus. A state hotline dedicated to tracking dead birds has logged more than 14,000 reports this year.
"The disease is so new in California, nobody knows how it's going to affect the state," said Dean Kwasny with the California Department of Fish and Game.
"A lot of these birds are fairly secluded. They use wooded environments so we don't know if they're picking up the disease and going off to these wooded environments to die."
Five years after West Nile virus was detected in New York in 1999, scientists say they are still trying to figure it out. Birds are natural hosts for the blood-borne virus, which is spread when mosquitoes bite infected birds and then bite humans or other animals.
But experts cannot say why some infected birds die immediately and others seem unaffected. Nor can they say how endangered species, such as the least Bell's vireo at Hansen Dam in the San Fernando Valley or the southwestern willow flycatcher along the Santa Clara River, will be affected.
"We're all watching the threatened and endangered species because they are already fighting a battle to survive," said Emi Saito, West Nile virus coordinator with the U.S. Geological Survey's National Wildlife Health Center.
"Is it going to affect the recovery of those birds or lead to ... extinction of those species?"
Officials were so concerned about the endangered California condor population that they began using an experimental DNA vaccine.
"We only have 200 birds left and they're all sitting in the West. With the condors, we just don't have the space to lose them," said Dr. Cynthia Stringfield, senior veterinarian at the Los Angeles Zoo.
The zoo vaccinated its 32 California condors last year. Zoo veterinarians are vaccinating their flamingos this year because East Coast zoos found the long-legged pink birds were hard hit by the virus.
Mammals, too, can be susceptible, and the zoo vaccinated elephants, rhinos and tapirs last year.
Beyond the zoo, scientists wonder what, if any, impact the virus will have on wildlife.
While most of the bird deaths this year have been recorded in Southern California, bird species considered at highest risk of dying from West Nile virus are in the Central Valley, the coast and western Sierra Nevada, according to a recent report prepared for the state by UC Davis.
Other areas are likely to have local declines in raptor or crow populations because of the virus. In Oklahoma, 40 percent of the crows tracked by officials died.
Experts cannot say if those were only temporary population dips or if there will be long-term ramifications.
"Everything in nature is connected," Saito said. "Because these are birds of prey, will these deaths lead to an increase in the rodent population that will lead to more rodent-spread diseases? What kind of impact will it have on insect-eating birds and species in the area?"
While West Nile virus is a worry, others say the region's bird populations face far greater threats from fires, development and invasive exotic species.
"West Nile virus is scary because of its (being) a disease, but draining a wetland will do a lot more damage to a bird or ecological community," said Dan Cooper, director of bird conservation with Audubon California. "There is so much happening in the state that is threatening many more species of birds and their populations."
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