If you go birding in a coniferous forest in the Pacific NW of the U.S. it's hard not to find these Chestnut-backed Chickadees Poecile rufescens. They are easily distinguishable from our other common chickadee, the Black-capped Chickadee Poecile atricapillus and the Mountain Chickadee Poecile gambeli by their chestnut colored back. Their call is different too, and they are pretty specific to coniferous trees, though in a mixed forest can be seen on leafy deciduous trees too.
Their range is pretty restricted to the northwestern U.S. and nearby Canada. This is the eBird range map.
Though their range map extends down the coast of northern California, once you leave the redwood forests of the far northern CA it's much easier to find them in western Washington and Oregon.
