Where are the “winter finches” this winter? The common red polls, American goldfinches, purple finches, and pine siskins? And where are the pine grosbeaks and the evening grosbeaks? Indeed, if your backyard birdfeeders are anything like mine this winter, then you’ve no doubt noticed a seeming lack of these species of songbirds.
An irruption is simply an influx of a species of bird into a geographical region not normally occupied by said species. According to Webster, the definition of an irruption of a natural population is one that undergoes “...a sudden upsurge in numbers especially when natural ecological balances and checks are disturbed.”
We typically observe this phenomenon during the winter months when birds migrate from the north to the south. Those birds most generally associated with winter irruptions here in northwestern Minnesota are birds such as those previously mentioned, including red crossbills, white-winged crossbills, and species of raptors such as the snowy owl, northern hawk owl, and great gray owl.
And some species of birds that we observe the year ‘round will sometimes shift their preferred wintering ground locations are black-capped chickadees, blue jays, red-breasted nuthatches, Bohemian waxwings, and varied thrushes.
Sudden appearances of the northern-breeding "winter finches" reminds me of a winter nearly twenty years ago (2001/2002) when huge flocks of the not-always-so-common, common redpolls dominated my feeders when I lived and worked at the Wetlands, Pines, and Prairie Audubon Sanctuary southeast of Warren, Minnesota. Never before, or since, had I enjoyed so many common redpolls as that winter.
Some people believe that seeing large numbers of uncommon birds, or birds not ordinarily observed in a particular area, as a sure sign of a harsh winter to come. Although this really isn’t the case, what it does mean is that species of birds migrating to wintering grounds not usually occupied (by them) are probably having a tough time elsewhere and are searching for more favorable areas.
In other words, food is the driving force and birds go where the food is. Yet it may also indicate a very successful breeding season. The influx observed could therefore be because there are too many birds for a limited food supply. Hence, more birds are observed elsewhere due to massive dispersals or, sometimes, in what are called “super flights.”
Though rarer than normal irruptions of a species or two on any given year, super flights are events like no other. In August 2012, for example, observers at Hawks Ridge, Duluth, recorded incredible numbers of red crossbills that were soon followed by waves of other species, such as red-breasted nuthatches, pine siskins, common redpolls, and others.
Finch experts differentiate between regional irruptions and super flights, not because of numbers alone, but by recognizing distinct differences in dialects of species across their range.
Red crossbills of the Pacific Northwest might look like red crossbills of northern Minnesota, but they don’t sound the same. As such, researchers and observers have been able to document birds from one part of the continent making their way to another part of the continent because of these audible differences.
As researchers at Cornell Lab of Ornithology explain it, “...super flights offer clues about what causes fluctuations in bird numbers and distribution.” And in order to transcend anecdotal information toward data that can be used, researchers often “...compile citizen-science reports and employ technological aids such as “smart feeders and sound-analysis software” in order to better understand super flight irruptions.
Just this past autumn while recreating out west, I observed large numbers of Clark’s nutcrackers in Colorado and an abundance of red crossbills in Nebraska. Whether or not I was observing local irruptions I can’t be sure, but seeing so many of each of these two species was remarkable nonetheless.
Maybe an influx of winter finches will happen here yet this winter. If not this winter, maybe next. Even so, the mysteries of annual migrations — from local and regional irruptions to super flights across the continent — are truly fascinating avian wonders as we get out and enjoy the great outdoors.