The mountain chickadee, known scientifically as the poecile gambeli, inhabits mountain forests and conifers in the spring, summer and autumn, and lower levels in the winter.
Adults of both genders have a black cap joining a black postocular stripe behind their distinctive white eyebrows. Their backs and flanks are gray and they have paler gray underparts. They possess a short black bill, and a black bib. The typical adult wingspan is seven-and-a-half inches, and the overall length is five to six inches.
Their call is a throaty chick-adee-dee-dee, while their song is a three-or-four-note descending whistle fee-bee-bay or fee-bee-fee-bee. They travel in pairs or small groups, and may join multi-species feeding flocks after their breeding season.
The mountain chickadee forages actively in trees, often feeding very high in conifers. These birds forage by gleaning food from twigs, often hanging upside down. They work along the trunk or major branches, probing in bark crevices. Intelligent creatures, they have been seen using a wood splinter to probe in deep cracks. They will sometimes take food from available sources while hovering. In interacting with humans, they will come to bird feeders for seeds or suet.
They feed primarily on insects, seeds, and berries. Their taste in insects is varied, including many caterpillars, beetles, and others. They often feed on insect eggs and pupae, as well as spiders and their eggs. They are not particular about what kind of seeds they will eat, as long as they are accessible. They are less eclectic with regard to fruits and berries, eating generally whatever is available in their habitat but not straying beyond their habitable limits to seek fruit elsewhere.
In some areas, the numbers of chickadees may be limited by a scarcity of good nesting sites. A good nest site usually consists of a hole in a tree, either a natural cavity or old woodpecker hole, or a cavity enlarged or excavated by the chickadees. These are usually at least five feet above the ground, ranging up to 25 to 30 feet, although some birds will nest in stumps only a few inches up from the forest floor, or a hole in the ground or occasionally a nest box offered by humans. The same site may be used more than one year. In natural sites in trees, both genders help excavate the location. The nest itself, which is primarily constructed by the female with generally minimal assistance of the male, is a soft foundation of bark fibers, moss, hair and feathers.
They breed monogamously, in a variety of coniferous stands, including forests of pine, spruce, fir, or Douglas-fir, as well as groves of aspen in coniferous zones, less often in pine-oak or pinyon-juniper, and very rarely in cottonwood groves in lowlands, producing one to two broods per year. Most often seven to nine eggs, usually white and dotted with reddish brown and sometimes unmarked, are laid, sometimes as few as five or as many as 12. The incubation by the female is 14 days. An adult disturbed on the nest will give a loud hiss, sounding like a snake. The young are altricial, i.e., helpless and highly dependent upon parental care, and stay in the nest for 21 days. Initially the mother remains in the nest while the male brings food; later both parents feed the young. First flight takes place at about three weeks.
Though yet widespread and common, chickadees have shown a downscaling in population, according to some surveys.
From the Audubon Field Guide and Wikipedia