Are they coming this winter or not? One hears this question a lot in birding circles at this time of year.

The question centers on the group of birds called the northern finches or winter finches – higher-latitude birds that grace us with their presence in some winters but not all. The only predictable feature of northern finch abundance is unpredictability.

The northern finches include the purple finch, pine siskin, evening grosbeak, pine grosbeak, white-winged crossbill, red crossbill and common redpoll. Although some of these species nest in Maine, most individuals nest well to our north.

All of these species depend on the seeds from trees for their sustenance, particularly during the winter. Redpolls are fond of birch seeds and the rest specialize on conifer seeds (firs, hemlocks, spruces, larches and pines). Pine grosbeaks have a taste for fruit as well.

When seed is abundant enough on the breeding grounds, these finches will forgo a southern migration and spend the winter on their breeding grounds. The birds spare themselves from the significant cost of migration. However, seed production by the trees the finches depend on varies dramatically from year to year. In a year of low seed production, the northern finches are forced to be nomads, wandering south until they encounter the seeds they need.

These southern migrations are called irruptions. The birds irrupt or move into areas away from their breeding grounds.

In our neck of the woods, three conditions have to arise for us to see an irruption of common redpolls, white-winged crossbills or other irruptive species. First, seed production on the finches’ breeding areas has to fail. Second, seed production of those trees has to be high in Maine. Third, the irruptive finches have to happen upon our abundant seeds in their wanderings.

For the past 20 years or so, Ron Pittaway in Ontario has been putting out a winter finch forecast. He gathers data on the cone production of various conifers, birch and fruit trees. He has been remarkably good at predicting flights of irruptive finches. His data for southern Ontario mirror those in neighboring provinces and states.

According to Pittaway, this winter will likely be poor in Maine for pine grosbeaks. Mountain ash in the boreal forest produced many berries this summer. Pine grosbeaks will have no need to irrupt.

On the other hand, cone production by several species of conifers across the boreal forest was modest at best. Pittaway expects white-winged crossbills, red crossbills and pine siskins to stage irruptions. Purple finches have already started to appear in Maine in good numbers at feeders.

The evening grosbeak has had a couple of excellent breeding years so its population seems to be on a bit of an upswing after several decades of decline. Pittaway thinks these birds are likely to be seen at feeders in southern Ontario and northern New England.

So far he seems right on the money. In the past week or so, I have heard reports of evening grosbeaks in Machias (100 birds), Newcastle, Bangor, Wells, Skowhegan, Gardiner, Milbridge, Pittsfield, Biddeford and Yarmouth. You get the picture: It is an irruption. I am not alone in hoping we have an abundance of these beautiful finches here all winter. Keep those sunflower feeders filled.

Red-breasted nuthatches depend on conifer seeds during the winter as well. Unsurprisingly, their irruptions tend to coincide with those of purple finches, pine siskins and white-winged crossbills. I’ve seen more red-breasted nuthatches this fall than I have in the past few years.

Blue jays also show irruptive behavior, responding to the abundance of their preferred winter food, acorns. Acorn production has been low this year in central Maine, perhaps because of the dry summer we had. Many of our blue jays will move south for the winter.

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

whwilson@colby.edu

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