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  National Geographic 16 May 07
West Nile Devastated U.S. Bird Species
Anne Minard for National Geographic News

Yahoo News 16 May 07
West Nile virus decimates suburban birds
By Seth Borenstein, AP Science Writer

Birds that once flourished in suburban skies, including robins, bluebirds and crows, have been devastated by West Nile virus, a study found.

Populations of seven species have had dramatic declines across the continent since West Nile emerged in the United States in 1999, according to a first-of-its-kind study. The research, to be published Thursday by the journal Nature, compared 26 years of bird breeding surveys to quantify what had been known anecdotally.

"We're seeing a serious impact," said study co-author Marm Kilpatrick, a senior research scientist at the Consortium of Conservation Medicine in New York.

West Nile virus, which is spread by mosquito bites, has infected 23,974 people in confirmed cases since 1999, killing 962, according to the Centers for Disease Control and Prevention.

But the disease, primarily an avian virus, has been far deadlier for birds. The death toll for crows and jays is easily in the hundreds of thousands, based on the number dead bodies found and extrapolated for what wasn't reported, Kilpatrick said.

It hit the seven species — American crow, blue jay, tufted titmouse, American robin, house wren, chickadee and Eastern bluebird — hard enough to be scientifically significant.

Only the blue jay and house wren bounced back, in 2005. The hardest-hit species has been the American crow.

Nationwide, about one-third of crows have been killed by West Nile, said study lead author Shannon LaDeau, a research scientist at the Smithsonian Migratory Bird Center in Washington.

The species was on the rise until 1999. In some places, such as Maryland, crow loss was at 45 percent, and around Baltimore and Washington, 90 percent was gone, LaDeau said.

While crows are scavengers and often disliked, they play a key role in nature by cleaning up animal carcasses, LaDeau noted.

Researchers will next look into what species benefit from the disappearance of crows. Researchers noted the die-offs came in patches, with many in some places and none in others. Maryland appeared to be the epicenter of bird deaths, though that was partly because the data were not as good from New York, where the virus first hit, LaDeau said.

Chickadees, Eastern bluebirds and robins in Maryland were 68 percent, 52 percent, and 32 percent below expected levels in 2005. Tufted titmouse populations in Illinois were one- third of what they were expected to be.

"It tends to be more suburban areas. Some of the common backyard species including the blue jays, the robins, the chickadees have suffered significant declines," LaDeau said. "That heavily packed urban corridor is a bad place to be a bird. The reason for that is that the mosquito prefers human landscape. They do very well in suburbia."

The birds act as an early warning system for humans, said Wesley Hochachka, assistant director of bird population studies at Cornell Lab of Ornithology.

"If you start seeing crows dying and dying in numbers, that means there could be a human outbreak," said Hochachka, who was not involved with the study.

The researchers looked at 20 species that were regularly counted each breeding season and found that populations of 13 species were not down because of West Nile.

Biologists say they have seen other species with many deaths, including owls, hawks, sage grouse and yellow-billed magpies, but there are no breeding surveys to quantify how bad the problem has been.

Although entire small clusters of crows were "wiped out by West Nile virus in a single season," Greg Butcher, director of bird conservation at the National Audubon Society, remained hopeful. "All of those (bird populations) have the capacity to rebound," he said.

On the Net: Nature: http://www.nature.com Centers for Disease Control and Prevention maps and figures on human cases of West Nile virus: http://www.cdc.gov/ncidod/dvbid/westnile/surv&control.htm surveillance

National Geographic 16 May 07
West Nile Devastated U.S. Bird Species
Anne Minard for National Geographic News

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.

Likewise, birds found to suffer the greatest West Nile death rates also do well around people. For crows, "the more dumps, the merrier," LaDeau pointed out. Not all of the 20 bird species studied in the paper showed the same response to the introduction of West Nile virus, though.

Crows, robins, chickadees, and bluebirds suffered steep, sometimes progressive, multi- year declines after the disease arrived.

Blue jays, tufted titmice, and house wrens, however, showed strong one- or two-year declines after intense West Nile virus epidemics, but little or no impacts at other times.

Blue jays and house wrens had rebounded by 2005, in fact. Other species seemed to do just fine in the face of West Nile. But that could be because the effects of the disease got lost in population fluctuations or long-term declines, the authors write.

Growing Problem

The study results raise new concerns about bird species that aren't included in backyard bird counts, LaDeau added. "We can't talk about impacts [of West Nile virus] to those species because we don't have the data," she said.

West Nile may be worst for bird populations when the disease is paired with other threats, the study authors point out.

In a May 12 press release commemorating International Migratory Bird Day, the American Bird Conservancy warned that migratory birds are still dying in large numbers from collisions with lighted buildings and communication towers, pesticide poisoning, and free-roaming cat predation.

New concerns, the organization said, include poorly placed wind farms and the spread of corn farming for biofuels, which may usurp vital bird habitats.

The conservancy organization estimates that more than a third of the 650 bird species that breed in the U.S. now have declining populations, are restricted to small ranges, or face serious threats.

Unanswered Questions

Leslie Dierauf is director of the National Wildlife Health Center in Madison, Wisconsin. She said the new Nature article is a good start because it's the first thorough look at the effects of West Nile virus on available bird numbers.

But it doesn't go far enough.

"I don't think they've brought enough of the complexities into the paper," she said. It's quite difficult to tease out all the interrelated factors that can impact bird populations, such as habitat, climate, and diet, Dierauf added.

The next steps include comparisons of how closely related bird species to the ones studied fared in the face of West Nile, along with other surveys, she said. Only then can experts make definitive conclusions about the West Nile's effects on U.S. birds.
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