What's the big deal? Consider this: These birds usually spend the winter in Canada and Alaska, and while they do appear in parts of the northern United States, they don't typically appear in places like Pennsylvania. Certainly not in gargantuan numbers. That is, typically.

When it comes to winter finches, the 1997-98 season has hardly been typical.

Since last fall, much of the United States has been experiencing a winter finch invasion of monumental proportions. During an invasion, one or more winter finch species moves south from their traditional wintering areas in what are called "irruptions." Evidence suggests that irruptions are associated with broad-scale changes in food supply in the species' traditional ranges.

Citizen scientists across the continent have been directly involved in monitoring this year's winter finch invasion by participating in the North American Winter Finch Survey, an online project that's part of the Cornell Lab of Ornithology-National Audubon web site, BirdSource <http://www.birdsource.org/>. Since mid-November, when the project first came online, more than 5,500 reports have come in, allowing BirdSource researchers to chart the whereabouts of Pine Grosbeaks, Purple Finches, Red Crossbills, White-winged Crossbills, Common Redpolls, Hoary Redpolls, Pine Siskins, and Evening Grosbeaks, as well as Red-breasted Nuthatches. Because of the state-of-the-art technology of BirdSource, Lab researchers were able to analyze these reports quickly and put findings up at the site in the form of animated maps illustrating the movements of each species throughout the winter. It didn't take long for the survey to show some interesting findings.

"It became apparent early on that the 1997-98 invasion was going to be extraordinary," says BirdSource project coordinator Steve Kelling, who developed the Winter Finch Survey. "By October 26, all of the winter finch species except Hoary Redpoll had been reported here in Ithaca. This hasn't happened in 20 years and never so early in the season." This prompted Kelling to devise the North American Winter Finch Survey. Before long, contributors were sending along some particularly noteworthy records.

In early November, more than 1,000 Pine Grosbeaks were observed at a hawkwatch in Duluth, Minnesota. Upwards of 800 have been reported in Maine. Hoary Redpolls were found in the Great Lakes area and into northern New England during the first 10 days of November--incredible when you bear in mind that during the massive Redpoll invasion of 1981-82, it took until mid-January for these arctic dwellers to show up in the States. And while Evening Grosbeaks do invade southerly regions like Tennessee, it's highly unusual for them to do so by mid-November, as they did this season.

There is a term for this phenomenon, when several winter finch species irrupt simultaneously. It's called a "superflight," a term coined by avian ecologist Carl Bock (Bock and Lepthien. 1976. Synchronous Eruptions of Boreal Seed-eating Birds. American Naturalist 110: 559-571). Little is known about why superflights happen some years and not others, though again, they seem to be associated with food availability. Crossbills and nuthatches feed on cone seeds; Redpolls forage on birch and alder catkins (the seed-bearing structures), and Pine Grosbeaks specialize in fruit seeds. The fruiting cycle of these different plants usually varies from species to species. This way, not all finch species are affected at the same time. At rare intervals, however, the seed crops of all or some of these plants are concurrently low. As a result, the birds' southward search for food may result in a superflight. According to Kelling, the last time a superflight took place was during the 1982-83 winter season. Before that, one occurred in 1968-69.

The North American Winter Finch Survey has shown that six species in particular have been dramatically associated with this year's superflight. These species--Red-breasted Nuthatch, Red Crossbill, White-winged Crossbill, Pine Grosbeak, Common Redpoll, and Hoary Redpoll--are particularly noteworthy because they're either appearing in unexpected locations across the country or are being reported in unusually high numbers--or both. For example, although Red-breasted Nuthatches sometimes move into parts of Texas during the winter, they're seldom reported as extensively and in such remarkable numbers as they have been this year.

The most exciting irruption is perhaps that of the White-winged Crossbill. This season has brought the species into areas that have not seen the bird since the 1970s, such as the mid-Atlantic states. An appearance of White-winged Crossbill in Tennessee is only the state's third record! But more remarkable than where the birds have been seen is in what numbers. One Pennsylvania locale observed more than 1,500 White-winged Crossbills! Huge flocks have also been reported in Washington State, New Jersey, Massachusetts--in all, there have been more than 40 reports of White-winged Crossbill flocks consisting of 100 birds or more.

Some of these vast numbers reflect an interesting metamorphosis that had taken place by midwinter. At the beginning of the season, winter finch observations were many but sightings were either of individual birds or relatively small flocks. As the season progressed, reports became fewer but flock sizes had drastically increased. (This, by the way, mirrors findings from Project FeederWatch published in the Winter 1996 issue of Birdscope.) In fact, many locations that reported winter finches near the beginning of the season observed few or none at all later on. Ithaca, New York, for example, saw early visits by both Red and White-winged Crossbills. But as the season moved along, these finches became exceedingly scarce in the region. Meanwhile, portions of Pennsylvania, New Jersey, Maryland, and Washington State were showing them in high numbers.

In light of this, Kelling added a simple question to the Winter Finch Survey form: What, if known, are the birds feeding on? The survey showed that areas hosting large numbers of Crossbills offered an abundance of food (White Pine and Eastern Hemlock in portions of Pennsylvania, New Jersey, Maryland, and Washington State; Pitch Pine and Japanese Black Pine in Massachusetts, Rhode Island, and the Long Island shoreline.) Conversely, the cone supply in central New York was negligible this winter. Regions rich with fruits and berries (much of New England) have maintained Pine Grosbeaks in high numbers; areas with scarce fruit and berry crops for the most part stopped reporting this species months ago.

Although day-to-day weather factors do not seem to trigger winter finch movements directly, large-scale weather events more than likely do, if only indirectly, through food-seed production. For example, El Niņo weather patterns may affect seed yield months or even years before the impact upon the birds is apparent.

Although the robins and blackbirds have returned here to Ithaca, New York, the North American Winter Finch Survey continues. Reports are still needed to learn more about the winter finches as they travel back to their breeding grounds. If you have observations of any winter finches or of Red-breasted Nuthatches, you're invited to report them to the survey at <http://www.birdsource.org>. Just click on "Winter Finch Survey" and follow the easy-to-use, scroll-down form. Also, view the animated maps and colorful graphs and enjoy the sounds and images of each of these distinctive species.