The Willamette Valley has been invaded by Mountain Chickadees this autumn. While more common at higher elevations, these chickadees are being seen regularly at feeders around the area.
As luck would have it, birder Craig Turner posted to OBOL that one was visiting his feeder at work in Wilsonville. Welcoming a rare sighting so close to home, I drove to the north side of town on December 1 and found it almost immediately.
There was some discussion as to whether this influx of Mountain Chickadees were of the Rocky Mountain or Pacific subspecies, with some leaning towards the less likely Rocky Mountain form in early discussions. Ultimately, I believe most settled on the Pacific subspecies.