- 6.3–7.9 in
- 1.1 oz
- Slightly larger than a Cassin’s Finch, considerably smaller than an American Robin.
- Merlebleu azuré (French)
- Azulejo pálido (Spanish)
- Historically, the Mountain Bluebird depended for nest sites on forest tree cavities excavated by woodpeckers. Today, many Mountain Bluebirds breed in artificial nest boxes, which tend to be situated in more open areas and have smaller openings to keep out marauders and bad weather. Most of what we know about Mountain Bluebirds comes from studies of these human-made nesting sites.
- A female Mountain Bluebird pays more attention to good nest sites than to attractive males. She chooses her mate solely on the basis of the location and quality of the nesting cavity he offers her—disregarding his attributes as a singer, a flier, or a looker.
- A male Mountain Bluebird frequently feeds his mate while she is incubating and brooding. As the male approaches with food, the female may beg fledgling-style—with open beak, quivering wings, and begging calls. More often, she waits until her mate perches nearby, then silently flicks the wing farthest from him—a signal that usually sends him off to find her a snack.
- Mountain Bluebirds compete fiercely with other cavity-nesters over nest sites. Early spring arrival at nesting grounds, for example, helps them take possession of choice cavities before Tree Swallows can appropriate them. Northern Flickers sometimes enlarge the entrance holes of nest boxes before discovering the box is too small for their own use—rendering the boxes permeable to weather and competitors such as European Starlings.
- The longest-lived Mountain Bluebird on record was nine years old when it was trapped and released during banding operations in June 2005.
During breeding season, Mountain Bluebirds seek out open areas with a mix of short grasses, shrubs, and trees, at elevations of up to 12,500 feet above sea level. They gravitate toward prairie and tundra edges, meadows, sagebrush flats, alpine hillsides, pastures, and recently burned or clearcut areas. Along roadsides, they seek out nest boxes or nesting cavities that face away from roads. Mountain Bluebirds winter at lower elevations—in meadows, hedgerows, prairies, and flat grasslands with few scattered trees and bushes, pinyon-juniper and oak-juniper woodlands, and agricultural areas. They avoid the most arid desert habitats.
Mountain Bluebirds eat mostly insects, especially during breeding season. Beetles, grasshoppers, and especially caterpillars top the menu. In winter they go after small fruits, seeds, and insects when available. Commonly eaten plant items include grapes, currants, elderberries, cedar berries, and the seeds of sumac, mistletoe, and hackberry. Spiders are also an important part of the adult diet. Nestlings are fed primarily beetles and grasshoppers.
- Clutch Size
- 4–8 eggs
- Number of Broods
- 1-2 broods
- Egg Length
- 0.7–1 in
- Egg Width
- 0.6–0.7 in
- Incubation Period
- 13 days
- Nestling Period
- 18–21 days
- Egg Description
- Pale blue to bluish white, rarely pure white, and paler than those laid by other bluebirds.
- Condition at Hatching
- Unfeathered, helpless.
Males sometimes enact a kind of symbolic nest-building—miming the act of bringing nesting material to the cavity, but actually carrying nothing, or else dropping their burdens en route. The female builds the insulated nest by herself, usually working hardest in the early morning. She entirely fills the cavity floor with coarse, dry grass stems and other vegetation, hollowing out a cup just large enough to allow her to cover her eggs snugly, with a maximum interior diameter of about 2 inches. The cup is usually greater than 2 inches deep, and placed as far as possible from the entrance hole. Cavity size determines the nest’s exact external dimensions. The female lines the cup with finer plant material, such as fine grass stems and narrow strips of soft bark, and also in some cases with wool or feathers. The whole process can take several days to more than a week. Mountain Bluebirds often reuse nest cavities with