Finch Irruption and Superflight
When Grosbeaks, Redpolls, Crossbills, and Siskins Migrate
Winter finches and seed eaters sometimes move in large numbers in search of food. Depending on bird numbers and geography, the movement is an irruption or a superflight.
Winter Finches
The winter finches of North America include Red and White-winged Crossbills, Pine and Evening Grosbeaks, Common and Hoary Redpolls, Pine Siskins, and Purple Finches. These birds, which frequent northern coniferous forests, are typically seen farther south only during the winter months when they move out of their summer range in search of food. A certain amount of movement is normal; however, in some years the birds move in unusually large numbers, and all of the species may move together.
Finch Migration
Movement of large numbers of winter finches is triggered by a poor seed crop in their normal range. For example, the summer of 2007 saw poor crops of rowan berries, hemlock cones, white pine cones, white and yellow birch catkins and alder catkins in large areas of central Canada. Meanwhile, spruce and fir trees produced an abundant crop on both the west and east coasts. This prompted predictions that grosbeaks, purple finches, and redpolls would move south, Red Crossbills would move west, and White-winged Crossbills and Pine Siskins would be seen in large numbers in both eastern and western Canada during the winter of 2007/2008.
Winter Finch Irruption
When large numbers of one species of bird move together to a new region, it is called an irruption. This isn’t a true migration; it’s more of a nomadic type of travel—going where the food is. Irruption is somewhat unpredictable though it does tend to coincide with years when seed crops are poor. And winter finches won’t necessarily return to their normal range to breed: some of these opportunists will breed wherever the food supply is good, at any time of year.
Finch irruptions are primarily of interest to bird watchers, but they are occasionally of economic importance when finches invade an area and target a commercial crop as a food source.
Winter Finch Superflight
A superflight occurs when all of the winter finches move out of their normal range in search of better seed crops. In these years, much larger numbers of birds move and travel farther than at other times. Some will be seen as far south as Texas, and other seed eating species, such as nuthatches, are involved as well.
Superflights, like irruptions, are unpredictable and often occur many years apart. Documented superflights occurred during the fall and winter of 1968/1969, 1972/1973, 1982/1983, and 1997/1998.
Data obtained from bird counts such as the Christmas Bird Count are useful in confirming both irruptions and superflights.
Sources:
Firefly Encyclopedia of Birds. Perrins, Christopher ed. Buffalo: Firefly Books, 2003
Superflight – Winter Migration of Finches. Cynthia Berger. National Wildlife: Dec/Jan 1998
Winter Finches. Audubon
Winter Finch Forecast 2007-2008. Pittaway, Ron. Northern Michigan Birding.
