Look who's coming to the feeder

If you don't know the difference between a mourning dove and a common ground dove; if you've never heard of the Sibley Guide to Birds; and if you've never thought of packing a pair of binoculars, a telescope, and a bird checklist and taking to the woods for a weekend - listen up: The Great Backyard Bird Count (GBBC), a four-day event that kicks off at dawn tomorrow, is the great leveler of bird-watching.

All you need is a patch of sky and a small interest in birds. More than 100,000 people have participated in the annual count, now being held for the fifth year. It is a joint project of the National Audubon Society and the Cornell University Lab of Ornithology, and an offshoot of the 102-year-old Christmas Birdwatch.

For ornithologists, it's the ultimate in what some call "citizen science."

On the one hand, the project seeks to further cultivate a burgeoning interest in bird-watching. The Cornell lab credits the famous Hedwig, Harry Potter's pet snowy owl, with increasing public recognition of a bird that has been making rare appearances in places such as Maine and New Hampshire. But, according to the February 2002 issue of Birding magazine, the popularity of bird-watching took off much earlier: by the early 1990s. Currently, some 70 million Americans call themselves bird-watchers - even if it means only putting out a feeder.

On the other hand, because the findings can be shared almost instantly over the Internet, the reports become the stuff of science: data points and percentages about bird populations in the winter.

How does it work? Anyone in North America can take part. Participants are asked to count and identify birds spotted in the backyard, schoolyard, local park, or other green space and to report their findings at www.birdsource.org. The website features ZIP code-based guidelines for what birds to look for, as well as tips for when and where to look. A map of the findings is refreshed hourly.

"It's a great thrill," says John Fitzpatrick, director of the Cornell lab, for people in a remote part of the country to see their dot appear on the map representing their findings. It's like being a voter in a small bellwether precinct during a close election.

For more serious birders, Mr. Fitzpatrick provides assurance that even with amateurs participating, the findings are turned into reliable statistics. Less than 10 percent of the findings that come in are suspicious or inaccurate, he says. Audubon and the Cornell Lab follow up those reports with phone calls to participants. Sometimes, when scientists are surprised by a report, it's not that the spotter has it wrong; it's that the bird is far out of its normal range. Among the most important findings of previous GBBCs is that some bird species, like the American robin, tend to avoid areas with lots of snow cover.

In the long term, Fitzpatrick hopes cumulative findings from the count will provide broader information about bird population trends in North America - ones that may reflect the effects of global warming. Already, he says, evidence exists that bird populations are drifting northward.