Watch those birdfeeders for rare northern finches visiting Western Pa.

Linda Croskey guessed it’s been about 30 years since she has seen the rare winter migrant, the evening grosbeak, show up at her birdfeeder at her West Deer home.

Then, after last week’s snowstorm, Croskey was elated to see at her feeder the rare visitor. It looks like an overgrown goldfinch with white patches punctuating shades of gold and yellow with an enormous conical beak known for its powerful crunching force — hence the name grosbeak.

It’s part of a “finch super flight” from the boreal forests in Canada. Known among scientists as an “irruption,” these northern birds dip down to the region intermittently when they are on the move looking for food.

“It’s the biggest irruption of evening grosbeaks in the region in more than 20 years,” said David Yeany, an avian ecologist with the Pennsylvania Natural Heritage Program and Western Pennsylvania Conservancy.

Yeany is in his third year of studying the migratory habits of the evening grosbeak with the Powdermill Avian Research Center in Cook Township, Westmoreland County, and the Finch Research Network.

He has been catching the birds in the Allegheny Forest in Marienville, his parents’ home, with a goal to outfit almost 50 grosbeaks with transmitters to learn more about migration and habitat use.

These rare northern finches are in steep decline. Population decreases have been estimated at 92% in the past 50 years, according to Yeany.

“We don’t know a lot about their ecology or winter irruptive movements,” he said.

In fact, Yeany contacted Croskey when he heard about about her grosbeak visitor: “Oh my gosh, I knew there was something different in my yard, and I was thrilled,” Croskey said.

Grosbeaks have been popping up in the region since October, with sightings in West Deer, North Park and other locations.

Other northern finches are irrupting, as well, including the pine siskin, redpoll, crossbill and purple finch, according to bird experts Brian Shema with the Audubon Society of Western Pennsylvania and Mike Fialkovich with Three Rivers Birding Club.

It’s a great year to watch a birdfeeder, Yeany said.

Irruptions occur when there’s a combination of lots of young birds hatched plus a bounty of meals to feed them. Yeany suspects outbreaks of spruce budworm, not treated with pesticides this year because of the pandemic, provided an ample food supply at first, then a decline in the seed production in conifers, maples and birches sent the birds packing for the south.

“When there are lots of birds and food shortages up north, they leave the boreal forests to find food,” he said. “And that’s how we get them in good numbers here in Pennsylvania.”

As the grosbeaks blow through town throughout the winter, they’ll feast on a smorgasbord of box elder, maple buds, crab apples, hawthorn berries and ivy berries.

One of the best ways to attract the birds to your feeder is to serve black oil sunflower seeds in a platform hanging tray or the ground, Yeany said.

Residents spotting a grosbeak with a colored leg band can alert Yeany via email at dyeany@paconserve.org.

To support the grosbeak research project, the conservancy is selling evening grosbeak T-shirts and hoodies via its website.