The Chestnut-backed Chickadee (Poecile rufescens, formerly Parus rufescens) is a small passerine bird in the tit family Paridae.

It is found in the Pacific Northwest of the United States and western Canada, from southern Alaska to southwestern California. It is a permanent resident within its range, but they sometimes fly short distances in winter when their food supply gets low. They usually move to lower elevations in the same area when winter starts and move back up to higher elevations in late summer.

It is a small chickadee, 11.5–12.5 cm long with a weight of 8.5–12.6 g. The head is dark blackish-brown with white cheeks, the mantle is bright rufous-brown, the wing feathers are dark gray with paler fringes. The underparts are white to pale grayish-white, with rufous or pale gray flanks. They travel in mixed flocks. They are often seen in large groups with bushtits and warblers.

There are three subspecies, with the flanks being grayer and less rufous further south (del Hoyo et al. 2007):

* Poecile rufescens rufescens (Townsend, 1837). Alaska south to northwest California. Broad rufous band on flanks.
* Poecile rufescens neglectus (Ridgway, 1879). Coastal central California (Marin County). Narrow rufous band on flanks.
* Poecile rufescens barlowi (Grinnell, 1900). Coastal southwestern California (south of San Francisco Bay). Almost no rufous color on flanks.

Its habitat is low elevation coniferous and mixed coniferous/deciduous forests. It is a cavity-nester, usually utilizing an abandoned woodpecker hole, but sometimes excavating on its own. Chestnut-backed chickadees use lots of fur and hair to make their nests. Their nests are actually 50% fur and hair. The most common hair they use comes from deer, rabbits, and coyotes. The adult chickadees also make a layer of fur about a centimeter thick which is used to cover the eggs on the nest whenever they leave the nest. It lays 5-8 (sometimes 9) eggs per clutch.

Its food is largely insects and other invertebrates gleaned from foliage. Chestnut-backed Chickadees take some seeds, especially those of conifers, and fruit. It will visit bird feeders, including hummingbird feeders, and especially loves suet.

Often, it is still placed in the genus Parus with most other tits, but mtDNA cytochrome b sequence data and morphology suggest that separating Poecile more adequately expresses these birds' relationships (Gill et al., 2005). The American Ornithologists' Union has been treating Poecile as a distinct genus for some time already.