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The BirdSource North American Winter Finch Survey is Tracking the 1997-98 "Superflight"

The BirdSource North American Winter Finch Survey Helped Track the 1997-98 "Superflight" During certain years, several winter finch species simultaneously irrupt into southern Canada and the United States from their normal wintering areas in the far North. This phenomenon is called a "superflight" (Bock and Lepthien, 1976, "Synchronous Eruptions of Boreal Seed-eating Birds," American Naturalist Volume 110: 559-571). Through BirdSource, the North American Winter Finch Survey tracked a major invasion of winter finches into the United States, and the 1997-98 winter season revealed itself to be a superflight year. As BirdSource mapped the movements of all nine species on the survey form, six species in particular--Red-breasted Nuthatch, Red Crossbill, White-winged Crossbill, Pine Grosbeak, Common Redpoll, and Hoary Redpoll--were most dramatically associated with this superflight.

It is unknown precisely why superflights happen some years and not others, though they seem to be associated with food production on the wintering grounds of these finches. Crossbills and nuthatches extract seeds from cones; redpolls forage on catkins (the seed-bearing structures of birches and alders), and Pine Grosbeaks specialize in fruit seeds. Typically, the fruiting cycles of these different plants vary from species to species, so that not all finch species are affected at the same time. (There is speculation that this variation in food production is an evolutionary strategy that forces these birds south every few years, thereby reducing their long-term impact on the plants.) When the seed production of all or some of these plants are affected simultaneously, the birds' southward search for food may result in a superflight.

Although weather does not seem to directly trigger winter finch movements, it is certainly a factor in food seed production. Therefore, a broadscale weather event that has taken place months or even years prior to an irruption impacts the seed crop, which then may lead to a superflight. Since Evening Grosbeaks, Pine Siskins, and Purple Finches forage on many of the same plant species as the other winter finches, it is still unclear why the numbers of these birds were not as strong during as they were for the other species.

The 1993-94 winter season saw an irruption that involved primarily redpolls. This is likely the result of the catkin production cycle of birches (Betula sp.) on the wintering grounds. This two-year cycle has been directly correlated to redpoll invasions. During years of low catkin production, redpoll numbers increase in the U.S; likewise, a good year for catkins usually means fewer redpolls coming into the country. The 1993-94 redpoll irruption was almost certainly due to a major decline in catkins. This same year, crossbills and Pine Grosbeaks were scarcely reported, suggesting that cone and berry crops were plentiful enough to sustain them on their wintering grounds.

As indicated on the animated maps, some parts of the U.S. have experienced only brief visits from winter finches during the 1997-98 superflight. This may be due to a lack of sufficient food to keep the birds in those areas. For example, relatively few reports of White-winged Crossbill came in in from Central New York, where the cone supply was negligible. On the other hand, the White Pines (Pinus strobus) and Eastern Hemlocks (Tsuga canadensis) in portions of Pennsylvania, New Jersey, Maryland, and northern Washington offered a robust quantity of food seeds for winter finches, according to reports from observers in these states. An abundance of Pitch Pine (Pinus rigida) and Japanese Black Pine (Pinus thunbergiana) cones in Massachusetts, Rhode Island, and the Long Island shoreline, and high tree and plant seed availability in much of the northeast seemed to have kept winter finches in these regions. Fruits and berries in much of New York and New England sustained the superflight in this part of the country.

The last time a superflight occurred was in 1982-83. There was also a superflight in 1972-73, and before that, in 1968-69.
Thanks for your helping us gather data about the 1997-98 superflight!