GUILDERLAND, N.Y. -- Liz Neill sprinkles a handful of sunflower and thistle seeds in her bird feeders and watches as a flock of birds circles her yard.
The veteran bird watcher says she has survived three bouts of cancer inspired by the appearance of cardinals, blue jays and chickadees outside her window. Now, she's returning the favor by helping scientists track changes in the bird population that could be associated with West Nile virus.
More than other creatures, birds act as reservoirs of the virus, which now is marching westward across the United States and has infected people or animals in all but four states - Oregon, Nevada, Utah and Arizona. Mosquitoes transmit the virus by first biting infected birds, then people.
According to the Centers for Disease Control and Prevention, more than 4,000 Americans, including about 3,900 last year, have contracted West Nile since it first surfaced in 1999. At least 252 people have died of the virus, most of them elderly.
From autumn's early frost to the first sprout of spring, Neill and a flock of volunteer bird watchers across the United States and Canada are helping track the virus by recording the number and species of birds that frequent their feeders.
"I'm concerned because birds are an integral part of our environment," Neill says. "They control the insect population and they're beautiful to look at."
West Nile is now carried by at least 100 species of birds, including the bald eagle and the endangered Mississippi sandhill crane. Crows and blue jays are the hardest hit but scientists believe smaller, uncounted birds also have succumbed to the virus.
"The primary victims of West Nile are birds, and we have basically no idea how important this is in terms of affecting bird population," says David Bonter, project leader for Project FeederWatch at Cornell University, which enlists 17,000 volunteers.
The watchers will record details on weather and length of time the birds stay, entering the information into a computer or on a tally sheet. Cornell ornithologists will then analyze the data to determine changes in population and distribution of more than 100 bird species.
If West Nile is killing off certain birds, Bonter says the scientists should be able to spot the trends in the data.
Neill, a 57-year-old social worker, is a devoted amateur scientist and particularly a fan of the chickadee for its "cheery, curious, fearless and energetic" behavior. Her rambling ranch-style home is a shrine to all things avian: bird and nature books fill bookshelves to the ceiling and bird figurines fashioned in stained glass seem to flutter in the windows. Her sweaters are decorated with bird designs.
On a chilly Saturday, Neill bundles up and waits for birds to perch on the dozen feeders dotting her quarter-acre of land six miles west of Albany.
Within minutes, a swarm of black-capped chickadees flock to a tree branch hung with a feeder. Brilliant red cardinals pop up on the fresh dusting of snow as hungry squirrels compete for food nearby. Finches, sparrows and even the predator Cooper's Hawk stop for a visit.
Neill spends eight hours every weekend counting birds for Cornell and can recognize 75 different species; her far-sightedness lets her spot them from 25 yards away. She even whistles some bird calls and is learning to train birds to sit in her hand.
It's not the first time these bird watchers have been tapped to help track an epidemic. In the 1990s, they chronicled signs of house finch eye disease, characterized by swollen, crusty eyes and blindness caused by a new strain of Mycoplasma gallisepticum - or MG - a bacterium that often causes respiratory infections in chickens.
Studies since the West Nile outbreak show that 77 percent of crows tested were found to carry the virus, and more than 95 percent of the infected crows died, says Robert G. McLean of the U.S. Department of Agriculture's National Wildlife Research Center in Fort Collins, Colo.
Results of the Project FeederWatch West Nile studies probably will not be published until later this year, Bonter said.
For Neill, taking part in the study is a way for her to give back to the birds.
When her mother and sister died less than three months apart in 1995, Neill got through her pain by listening to birds chirp. Last year, while undergoing radiation to treat a rare cancer invading her salivary glands, she found peace swinging in her backyard hammock surrounded by songbirds.
"I wish to be the steward of the land and take care of nature," she says. "My role is to be the eyes and ears for the scientists out in the field."
On the Net:
Project FeederWatch: http://www.birds.cornell.edu/pfw