Will they come or not? With winter approaching, it’s time to think about northern finches. A suite of finch species breeds mostly to our north in the expansive boreal forests of Canada and Alaska. Like other finches, these northern finches depend on seeds from conifers and other trees for their sustenance.
We know that seed production by trees varies greatly from year to year as well as place to place. When seed production is high on the breeding grounds of northern finches, they forsake migration and tough out the extreme northern winter. No problem if food is adequate.
But in years when seed production is poor, those birds are forced to migrate south in search of food. We call these movements irruptions.
Seeing an irruption of crossbills, redpolls or Evening Grosbeaks depends on low seed availability in the north and high seed production in our area. Abundant seed crops here are not guarantee that we will see northern finches. They might find sufficient elsewhere and our productive seed crop may be untapped. Good for the trees but not for seeing northern finches.
For years, Jean Irons and Ron Pittaway, and now Tyler Hoar, in Ontario have been examining the spatial distribution of seed crops in northeastern North America to lend insight into the likelihood of good finch irruptions.
Let’s start with the crossbills. Our two crossbill species are among the most specialized foragers in North America. Their peculiar, crossed bill is perfect for inserting between two overlapping scales of a conifer cone. They then use their spear-like tongue to extract the seed at the base of the lower scale. Their bills are do their single job well but function poorly in feeding on other types of food. So, crossbills must find adequate cone crops.
White-winged Crossbills have smaller bills and weaker jaw muscles than Red Crossbills and hence specialize on smaller cones. Black spruce are the favored cones with hemlocks providing a second choice. Other cones are used only in desperate times.
Hoar reports that spruce cone availability in western North America is high and relatively poor in our part of North America. Expect few white-wings this winter.
Red Crossbills can accommodate bigger cones with their sturdier bills. They use a wider diversity of cones than white-winged crossbills and even the toughest, largest cones can have their seeds stripped by red crossbills.
However, the situation is quite complicated with Red Crossbills. Researchers have identified ten distinct types of red crossbills, based on morphological differences as well as distinctive call notes. See the Finch Research Network to find information on identifying the types of Red Crossbills.
Here in New England, we expect to see the Northeastern Red Crossbill and occasionally Appalachian Red Crossbill with medium-sized bills. But, in some years, we see an influx of mainly western morphs like Ponderosa Pine Red Crossbills with their massive bills and Western Hemlock Red Crossbills with small bills.
Red spruce and white pine cone production was strong this summer in Maine so we expect good numbers of northeastern Red Crossbill types this summer although they may migrate further down the eastern seaboard as our cone supplies are depleted.
Pine Siskins prefer the cones of eastern white cedars. In the northeast, we have a strong crop of these cones so siskins should be around for at least the first part of the winter. Many will move south as cones are depleted here.
Common Redpolls specialize on birch seeds. Birch seed crops in the boreal forest were poor this year so look for a moderate flight of these delightful birds into Maine.
Evening Grosbeaks are enigmatic, but Tyler Hoar believes we will entertain these charismatic birds this fall and winter. Fingers crossed!
Purple Finches will likely winter south of this year. Pine Grosbeaks, a fruit-eating finch, will likely appear this winter because of our great mountain ash berry crop.