The year 2020 will be remembered for a lot of reasons, but for birders across the country, one of them will actually be good: the biggest irruption of northern finches in recent history. This year has seen huge movements of these birds southward, and many have reached astonishing places far from where you’d expect to find them.
Finch researchers are calling this year a “superflight,” where every species of boreal finch is irrupting, or moving southward in search of food. A perfect storm of feast and famine appear to be driving this banner finch year, affecting Common and Hoary Redpolls, Evening Grosbeaks, Pine Grosbeaks, Pine Siskins, Red and White-winged Crossbills, and Purple Finches. Other irruptive passerines, like Blue Jays, Bohemian Waxwings, and Red-breasted Nuthatches, are also on the move. "There's not enough food to support them, so they’re just spilling out of the boreal forest.” says Matt Young, ornithologist and founder of the Finch Research Network.
Many of North America’s finches live in the forests of Canada (and in northern parts and higher elevations of the United States), where they rely on a selection of conifer or other boreal trees for food—especially their fruits and seeds in the winter. However, many of these trees produce food in cycles, supplying an abundance of seeds in “mast years” and very little to no sustenance in other years. Birds dependent on these trees undergo movements in response to these cycles, staying and breeding in areas where seeds and fruits are plentiful and heading elsewhere when crops fail. In a meager year for seed stocks, birds will dip southward in search of food, and during a widespread crop failure, they venture far into the United States to find sustenance. This is one of those years.
Scientists think the trees evolved these synchronous mast-crop cycles in order to limit the food supply for seed-eating squirrels, preventing their populations from growing too large and eating all of the seeds, explains Jamie Cornelius, an assistant professor at Oregon State University who studies crossbills and is a member of the Finch Research Network. But unlike the squirrels, “birds are mobile, and can find cone crops somewhere else,” she says. In some cases, these birds have evolved strategies to cope with the occasional crop failures; crossbills molt slowly, for example, so they can be ready to fly at any moment should food run out.