It is that time of year again -- when the weather gets colder and many people become concerned about the wild birds in their yards and they begin bird feeding. This is also the time of year that people who feed birds can join the 15,000 other people who are a part of the largest and longest running citizen-science project.

Project FeederWatch, a winterlong survey of birds that visit feeders at backyards, nature centers, community areas and other locales, began in Ontario, Canada, in the mid-1970s. After running for 10 years, it was expanded to the United States with the help of the Cornell University Laboratory of Ornithology.

FeederWatch volunteers periodically count the highest numbers of each species they see at their feeders from November through April. The project helps scientists track movements of winter bird populations and long-term trends in bird distribution and abundance.

All you have to do is count all the birds in your yard at one time, then report the numbers to the lab. The data collected show which bird species visit feeders at thousands of locations across the continent every winter. The data also indicate how many individuals of each species are seen. This information can be used to measure changes in the distribution and abundance of bird species over time.

Each year, the population level and distribution of each species fluctuates. For example, this year in the western parts of the country, drought and forest fires have reduced natural food sources, so birds may be forced out of the mountains to lower elevations, where they can find more food, including at bird feeders.

If people do not keep track all over the country, we would not see the weekly changes in distribution and abundance. This data is important because it provides information about bird population biology that cannot be detected by any other easy method.

Some of the scientific information that can be collected by using citizen-scientists is not just in the short term; long-term trends in bird distribution and abundance, the timing and extent of winter irruptions or invasions of winter finches and other species also can be seen when the study is repeated each winter. Also, expansions or contractions in the winter ranges of feeder birds, the kinds of foods and environmental factors that attract birds and how disease is spread among birds that visit feeders can be determined. FeederWatch data is used to gauge the impact of West Nile virus on wild birds.

Help monitor the health of winter bird populations by joining in the 17th season of Project FeederWatch. Learn more about the project at www.birds.cornell.edu where you can see maps, trend graphs, and other results generated from FeederWatch data. FeederWatchers receive a research kit that includes a FeederWatch handbook, a guide to feeding birds; a full-color identification poster of common feeder birds (both Eastern and Western, painted by renowned artist Larry McQueen); a 14-month calendar featuring photographs taken by FeederWatch participants last season; instructions on how to participate; and paper data forms or access to the online data entry system. In addition, participants receive a subscription to the newsletter of the Cornell Lab of Ornithology.

A $15 annual participation fee ($12 for members of the Lab of Ornithology) covers materials, and staff and Web support. For more information, call (800) 843-2473.