These incursions of boreal species into the northern and middle United States are known as irruptions. Irruptions are highly irregular mass movements of northern species thought to be precipitated by a shortage of food in the birds’ normal range. Some species thought of as “irrupters” include Bohemian waxwing, pine and evening grosbeaks, red and white-winged crossbills, common redpolls and pine siskins.
Of course, what’s an irrupter depends on where you are, too. I wouldn’t consider pine siskins irrupters here in Western North Carolina above 3,500 feet or so. I have them at my feeders every winter. However, pine siskins in the upstate might be considered irrupters.
If memory serves me correctly (and often it doesn’t), I believe 2001 was the last year I had evening grosbeaks at my feeders. But with early sightings in Catawba County and predictions of poor seed crops in northern boreal forests, the hordes may return. I would surely love to have evening grosbeaks at my feeders this winter, I just hope I can afford it — you would be amazed at how many black oil sunflower seeds a flock of these critters can go through.
You won’t be able to miss these large yellow, black and white finches. Juvenile common redpolls are small brown-streaked finches that could be confused with pine siskins and/or female house finches but with their late summer molt they take on the red cap and dark chin of the adult so birds here, in the winter, should be easy to distinguish if you get a view of the head. Common redpolls are similar to hoary redpolls in all plumages. But as the name “hoary” suggests, the latter is paler all over and the streaking on its flanks and rump are minimal or absent. Hoarys rarely make it this far south even in irruption years.
If you think you have a redpoll at your feeder it’s best to try and document it immediately. The birds are quite transient and that one stop at your feeder may be the only one.
It makes for pretty interesting reading.