Common redpolls are one of my favorite birds. To have dozens of these delightful sprites fighting over the nyger seed (marketed as thistle seed) at our feeder is always a joy.

But, alas, redpolls do not visit us every winter. Every November, I start to wonder if the coming winter will be filled with redpolls here in Maine.

Common redpolls belong to a group of finches called the northern finches or the irruptive finches. This group of birds includes the common redpoll, along with the less common hoary redpoll, pine siskins, pine grosbeaks, evening grosbeaks, red crossbills and white-winged crossbills. Most individuals of these species nest north of us. In some years, these birds will spend the winter on their breeding grounds, but in other years they move south to places like Maine or even further south. The birds erupt from their northerly breeding grounds and irrupt, or move into, more areas to the south with more moderate winters.

It’s not the cold, per se, that drives these irruptions. Rather it is the availability of food. If sufficient food is available, common redpolls can pass the winter above the Arctic Circle. Those metabolic challenges cannot be met when birds cannot acquire enough food to stoke their internal furnaces.

In the case of irruptive finches, the food required is seeds. Redpolls are fond of birch seeds, pine siskins and purple finches use the seeds from conifers with smaller cones (spruce, firs, hemlocks, larch), while evening grosbeaks and crossbills can handle large cones of pines. Pine grosbeaks are a bit unusual in that they depend on fruits.

We know that seed production varies greatly from year to year. Trees of a particular species are synchronized in their reproduction. So, over broad swaths of forest, red spruce may produce prodigious amounts of cones in one year, followed by several years of modest to low production. A year of plenty is called a mast year.

This variability of seed production is thought to be an adaptation against seed predators (insects, birds, squirrels). Low seed production keeps the seed predator populations low, and then a mast year overwhelms the capacity of the seed predators, giving many of the seeds a chance to germinate.

During mast years for the tree of choice, northern finches do not need to migrate south for the winter. In years of moderate production, some finches will irrupt. It is only when seed production is poor that we see massive influxes of northern finches.

What will the winter of 2018-19 bring for northern finch abundance? Ron Pittaway, a birder in Ontario, offers a prognostication every fall for the strength of the irruption of northern finches. He bases his predictions on reports of cone and seed production. Although his predictions are specifically geared to Ontario, the patterns he describes are applicable to northern New England and the Maritime Provinces.

Pittaway reports that birch and cone crops are poor to low in most of Ontario and northeastern North America with the exception of Newfoundland, which has a bounteous spruce crop. We can expect an irruption of winter finches into southern Ontario, southern Quebec, the Maritime provinces, upstate New York and New England. Yippee!

The first common redpolls should be arriving soon. Look for them in weedy fields. Once they discover nyger seeds at people’s feeders, feeding frenzies can ensue. Let the chaos begin.

Pine siskins are on the move already, and some may continue farther south or west. The same pattern may occur in purple finches.

Evening grosbeaks are expected to stage a moderate flight south this year. I have already heard of several sighting of these gluttonous beauties at feeding stations in Maine.

Mountain ash berries are scarce to the north of us, so the dearth of food should push pine grosbeaks into Maine this winter.

Herb Wilson teaches ornithology and other biology courses at Colby College. He welcomes reader comments and questions at

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