This chickadee can be found above 12,000 feet, sometimes to timberline and beyond. It spends a lot of time in the postbreeding season caching conifer seeds for the winter. It forages higher in tall trees than most chickadee species, and it often spends the nonbreeding season foraging in flocks with chestnut-backed and black-capped chickadees, as well as migrating passerines, including warblers and vireos. Polytypic. Length 5.3".
The white supercilium, which consists of white-tipped feathers, is unique among chickadees. Black cap, usually fronted by a white forehead that connects to the supercilium; black bib; white cheeks; grayish, brownish, or olive upperparts, depending upon the subspecies; greater wing coverts, secondaries, and tertials indistinctly edged with pale gray; dull white breast and belly; pale buff to drab gray, sometimes washed olive, sides and flanks.
Four subspecies in North America, plus another in Mexico—only 2 are field-identifiable. Nominate gambeli in the Rocky Mountains, the most wide-ranging subspecies, is tinged with buff or brownish olive on the back, has buffy sides and flanks, and has a prominent white supercilium. California’s baileyae is entirely grayish on the back, sides, and flanks, sometimes with a slight olive tinge. It has a less distinct supercilium than gambeli. The other subspecies have various features intermediate between these two.
When the supercilium is less conspicuous, as in the western subspecies, or when the feather tips are worn, a mountain could be confused with its closest relative, the black-capped. The latter sometimes has a hint of white in its superciliary area, but this condition is very rare. The wing edgings offer the most helpful distinction between the two: pale gray and inconspicuous on the Mountain, prominently white on the black-capped. The Mountain’s small bib should distinguish it from a Mexican chickadee. A vagrant of the Rocky Mountain subspecies with a worn eyebrow might be troublesome in the westernmost Carolina chickadee range, but the Mountain is noticeably larger, and its upperparts are brownish or olive in contrast to the Carolina’s dull gray upperparts.
Call: a hoarse chick-dzee-dzee-dzee, as well as a variety of buzzes and chips. Song: typically a 3- or 4-note descending whistle, fee-bee-bay, or a fee-ee-bee-bee on 1 pitch, with many local dialects. The fee-bee-bay version has been compared to the melody of “Three Blind Mice.” Some of its vocalizations are very similar to those of the black-capped, and a good look may be necessary to ascertain the species.
Status and Distribution
Common. Breeding: primarily found in montane coniferous forests and mixed woodlands, but locally in pinyon-juniper and desert riparian woodlands. Sometimes use nest boxes. Winter: some descend to lower elevations in foothills, riparian woodlands in valleys, and suburban areas, where it sometimes visits feeders. More or less regular to coastal California; more rarely to southern Arizona. Vagrant: casual, mostly in winter, east to Saskatchewan, North Dakota, South Dakota, Kansas, Nebraska, Oklahoma, and the Texas Panhandle.
Breeding bird surveys show a long-term decline in many parts of the mountain’s range, but the causes have not been established.
—From the National Geographic book Complete Birds of North America, 2006