Female common redpoll eating alder seeds at Northwestern University. (Photo: Fran Morel)

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The redpolls are here! There’s excitement in the air, literally. Redpolls are adorable, active, gregarious little finches with heavily streaked sides, forked tails, yellow bills, a black chin and, most importantly, a red forehead, or “poll” as it is called. The males have a beautiful rose blush on their upper chests, giving them a jewel-like appearance.

During a typical winter in Evanston, small birds that can be seen are resident American goldfinches, house finches, house sparrows, northern cardinals, black-capped chickadees, white-breasted nuthatches and the dark-eyed juncos that come south for the season. All visit feeders.

But 2021-2022 has not been a typical winter. By early December, common redpolls, carduelis flammea, birds in the finch family, began to enliven our winter scene and sometimes displaced the usual suspects at feeders. One or two or a flock of more than two dozen might descend, seemingly out of nowhere. Redpolls are constantly in motion, often chattering away. They are so approachable that one can stand quietly only a foot or two away without disturbing them.

Finches are small songbirds with beaks capable of crushing seeds. As seedeaters, redpolls are dependent on seed production in their native habitat, although they do feed their nestlings protein-rich insects. They make their home in the worldwide subarctic edge of the tundra and boreal forest. They prefer open habitats with scattered scrubby thickets of dwarf birch, spruce, willow and alder that provide nesting grounds and food.

As residents of the subarctic, redpolls are particularly well adapted to cold and can survive temperatures of -65F degrees. They add plumage for the winter months, and they have a throat pouch for temporary storage of seeds so they can digest them throughout the night in a quiet sheltered spot away from predators. In the recent mid-February drop in temperatures and blowing snow in Evanston, the redpolls were still at a swaying feeder at 4:50 p.m., presumably tanking up for the chilly hours ahead.

Predicting a year of ‘irruptions’

In a typical year, a few redpolls, or none, may be seen in the Chicago area. “Irruptions,” as we are seeing now, with hundreds of redpolls reported in our area, occur when demand for food outpaces the supply in the normal habitat of a species. The irruption of snowy owls several years ago followed a bumper crop of food supply, which led to a bumper crop of young, which led to a need for the young to spread out to find a reliable food source during the winter. The redpoll irruption is not caused by too much breeding success. It is, instead, caused by the failure of its food supply of seeds on their usual wintering grounds.

Ron Pittaway, a Canadian naturalist, began predicting winter finch irruptions, or lack thereof, in 1999. His prediction was based on reports from a vast network of observers who communicated the conditions of the summer seed supply where the birds would typically remain for winter. As The Cornell Lab of Ornithology’s All About Birds writes: “Pittaway claimed his forecast is an art rooted in science.

“When the conifer trees are bumper [crops] and the cones open, the birds just need to reach into them and pull the seeds out. There’s food everywhere,” said Pittaway. “When there is so much food of a bunch of varieties, the birds stay north. But if there’s a drought, or a frost in June, or other disruption that interferes with seed production, the seed crops fall below normal, and thousands of finches burst from the boreal forest and move south into the U.S. to search for food.

Male redpoll (Photo: Creative Commons)

“My forecasts try to make sense of what might happen based on tree seed crops and knowledge of past irruptions,” he continued. “Last year [a big irruption year] was easy, because there was no food. This year [a non-irruption year] was easy, because there was a superabundance of food. But there are lots of years that are in between. Those are the hardest years to predict.” 

The Cornell Lab explains further: “Different tree species produce bumper crops at varying frequencies. Eastern white pine, for example, will produce a bumper crop every three to five years, but rarely churn out two good years in a row. Eastern hemlock, on the other hand, will furnish a good crop every couple of years. The quality of the crop – good or bad – tends to be stretched out over hundreds or even thousands of miles of forest, forcing the birds to travel long distances to keep pace with the boom–bust cycle of food.”

Pittaway retired last year, handing the job over to a colleague, who predicted that 2021-2022 would not be an irruption year. Perhaps this was a year that was in between. To the delight of many, and despite the prediction, redpolls have come to winter in Evanston. Feeders filled with fresh thistle or nyjer seed or sunflower chips are most productive for attracting them. 

Judging from Evanston North Shore Bird Club Christmas Bird Count data, recent irruptions here were in 2015 and 2017, with 2021 substantially exceeding the number from earlier years. This winter, observers have reported redpolls at Northwestern University’s south parking lot where there are stands of seed-bearing alder trees (see photo), at the Chicago Botanic Garden among the catkin-bearing birches outside the visitor center, and at LaBagh Woods Forest Preserve in Chicago. The redpolls should be here until mid-March, though there is no predicting exactly where they will be.no

Libby Hill

Libby Hill is the author of "The Chicago River: a Natural and Unnatural History. She has been writing about birds and trees and Evanston's natural history for the Roundtable since 2004.

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