It’s official: We’ve just seen the largest movement of evening grosbeaks into Pennsylvania in 20 years Updated Feb 25, 2021; Facebook Share Winter 2020-21 brought the “largest irruption of evening grosbeaks in over 20 years, a massive movement out of the boreal forest,” according to David Yeany II, avian ecologist with the Western Pennsylvania Conservancy. That declaration during a recent WPC webinar on its developing study of evening grosbeaks will come as confirmation to backyard birders in many spots across Pennsylvania. They’ve seen flocks of the bright yellow birds with the outsized beaks at their backyard feeders in the past several weeks, often for the first time.