Resident from extreme southwestern British Columbia, southern Idaho, southwestern Wyoming, and Colorado southward. Also found along the Pacific coast states and south into inland Mexico. The preferred habitats include coastal forests among second-growth alder thickets and edges of coniferous forests composed of maple, dogwood, and birch. Both the male and female will incubate the eggs, sometimes even at the same time. Bushtits travels in flocks of up to 60 birds until breeding season when they break off into pairs.
The nest is an impressive, woven, hanging basket with a hole high up on the side of the nest and a passageway to the nest chamber at the bottom. It can be up to a foot long, and is generally built of spider webs, moss, lichen, and other plant material. This bird often has helpers at the nest, birds other than the parental pair that feed nestlings. All family members sleep together in the complex nest during breeding, but they leave it after the young fledge, and sleep on branches.