I had three species of chickadees attending my feeder recently. The Black-capped Chickadees are year-round residents and visit every day.
The star attraction on this day was a Mountain Chickadee. While common along the crest of the Cascades and points east, they are a rare treat in the Willamette Valley. This bird is the seventh record for Washington County.
I believe the Pacific Northwest is the only place where you might find three species of chickadees in one flock. Range maps indicate that in southeastern Alaska, you might be able to find four species in the same area. That sounds like a worthy birding challenge.