Not “eruption,” which is a violent bursting out, but “irruption” which is a bursting in, an invasion.
This winter is an irruption year for birds. Three of the invaders are pictured here by Mark McConaughy at Bushy Run Battlefield’s feeders. They are common redpolls, a very small finch with a red cap and black chin who normally lives in the boreal forest and taiga of Canada and Alaska. (The male has a rosy chest.)
Last Sunday I went to Bushy Run to see these tiny invaders because I hadn’t seen them for 10 years – not since the irruption of 1997-1998. That’s how infrequently they come this far south.
Why do they stay north most years but visit us occasionally in winter? Ron Pittaway of Ontario Field Ornithologists monitors food supplies in the northern forest and makes a winter finch prediction every year. This year the tree seed crops of birch, alder, spruce and fir are all quite low. The winter finches would find little to eat in Ontario. He predicted an irruption.
Redpolls, who thrive on birch and alder seeds, are not the only species to invade southwestern Pennsylvania this winter. Others include:
- Evening grosbeaks, a large yellow seed-eating finch with a very large beak (‘gros’ means large in French). Evening grosbeaks used to be abundant but are declining because their summer food, the spruce budworm, has declined in recent decades.
- Pine siskins, a small, brown, striped finch with a yellow splash on his wings and tail. Pine siskins eat spruce and fir seeds in winter. They also visit feeders.
- Northern shrikes, a predatory songbird who eats birds, insects and small mammals. The shrike doesn’t have sharp claws so he must impale his prey on spikes or barbed wire to eat it. This bird came south because his prey did.
I saw a northern shrike in November at Moraine State Park and redpolls last Sunday. I’m still hoping to see evening grosbeaks and pine siskins before the irruption ends. I almost want winter to last a little longer so I have more time. Can you believe it!
(photo by Mark McConaughy)
Thanks for explaining what “irruption” means in the bird world. I’d seen the word on the PA Bird List — now I know — and I also know why everyone is so excited about seeing redpolls this year. Back in the 60’s, we used to enjoy a big flock of evening grosbeaks — in the Springfield MA area. They’d land in a big elm (!!) — 50 or more — and come in to clean out my mother-in-law’s feeder of all the sunflower seeds. I’ve seen just one or two in recent years.