Fall Focus on Finches

At ZNE’s Field Conservation department, we’re always paying close attention to the behavior of animals as the seasons shift. Every species has its own needs, and they have all evolved specialized behavioral strategies to meet those needs. Fall follows summer and in turn gives way to winter every year, and so the plants and animals change their rhythms to cope. Of course, not all years are created equal, and savvy species will show some flexibility in their behavior to take full advantage. For example, this year had a very wet summer and a mild fall, so many of the turtles we track have been taking advantage of higher water levels and warmer temperatures to remain active a little later in the year than they might otherwise manage. If you’re looking for a terrific example of behavioral flexibility (what scientists call plasticity) right in your own backyard, look no further than the visitors to your bird feeder – especially finches.

Two small, streaky brown-and-white birds, one with a cherry-red cap, forage alongside a larger, stockier bird with a heavy bill and greenish-yellow head and rump. All three birds are picking small black seeds off the snowy ground.
A pair of redpolls and a pine grosbeak dine on seeds scattered around the snow. Image credit: Per, via Wikimedia Commons. Licensed under a Creative Commons Attribution-Share Alike 2.0 Generic License.

Finches are small songbirds that eat mostly seeds and fruits in the fall and winter while foraging during the warmer months for protein-rich insects for themselves and their young. Conifer seeds especially are an important winter food source for finches of all kinds, but many conifer species have “mast year” seeding patterns – years when they produce a huge number of seeds, followed by several years of only producing a few. This unpredictable schedule is believed to evolve to control populations of seed predators like squirrels, preventing them from becoming so numerous that they eat all the seeds in a given area. This also makes the finches’ winter food supply unpredictable for them, but during a lean winter, birds can do something that squirrels can’t: fly somewhere else!

A red bird with black wings and tail uses a bill that crosses at the tip to pry seeds from conifer cones as it perches on a twig, needles and cones all around it.
Red crossbills specialize in eating the sees of conifer cones. When the cone crop fails, the crossbills move together en masse to a new location with better foraging opportunities. Photo credit: Mike Pennington. Licenses under a Creative Commons Attribution-Share Alike 2.0 Generic License.

When large numbers of some finch species come south into the United States from the boreal forests of Canada where they normally live, we call it an irruption. Distinct from annual migration, irruptions occur in response to local food conditions and don’t happen every year. 2020 was one such irruption year – the Covid-19 pandemic reduced Canada’s ability to spray for spruce budworm moths, which in turn produce huge numbers of larvae. Finches raised large broods of young on this abundant insect food, but once fall came, the spruce cone crop was a poor one. The combination of unusually high numbers of hungry birds and unusually little seed for them to eat caused a large-scale irruption. Backyard birdfeeders throughout the US welcomed record number of pine grosbeaks, evening grosbeaks, pine siskins, redpolls, and other winter finches. Then, when spring came, the birds returned north to their breeding grounds. 

What does 2021 have in store? It’s hard to say for certain, but the experts at the Winter Finch Forecast say that this year won’t be anything like last year, and many boreal finches will be staying in the far north. They do, however, note that there has already been significant movement of nomadic white-winged crossbills towards northern Maine and the Canadian Maritimes, so they may be present in southern New England this winter. Evening grosbeaks are also predicted to have a smaller “echo flight” southward after last year’s record-breaking irruption, and they may turn up at feeders – so keep your eyes peeled! 

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