Bird of the Month: Mountain Bluebird

By Andy McCormick

Scientific Name: Sialia currucoides

Length 7.25 in

Wingspan 14 in

Weight 1 oz (29 g)

AOU Band code MOBL

The Mountain Bluebird, sometimes called the “prairie bluebird” (Dunne), is a bird of open grasslands. It is seen most frequently in Central and Eastern Washington. It enjoys a wide range of habitats including an altitudinal range from grasslands to open areas in forests, to alpine tundra (Alderfer).

Electric Blue – Structural Coloration

The serene cerulean blue of the breeding male Mountain Bluebird is what people love about this bird. It is captivating, and on sunny days, it is brilliant. The color results from the interaction of light with the structure of the feathers. This phenomenon is limited to the colors blue, violet, and indigo, which have short wave-lengths. When light is reflected from certain structures in the bird’s feathers only the short wave-length colors are reflected and the human eye sees blue. “No blue pigments have ever been discovered in the feathers or skin of birds” (Hill). Bluebirds are quite beautiful and “many people view bluebirds as an emblematic species representing all that is good in the world”

(Power and Lombardo).
This color of the male is also important in mate selection. Studies have shown that females prefer brighter blue males. Female Mountain Bluebirds will select additional males for extra-pair copulations. Researchers have observed that the most brilliant blue males will sire more extra-pair offspring, inferring that females choose brighter males to be their mates (Hill).

Cavity-nesting Thrush

The Mountain Bluebird is a cavity nester and will build a cup nest made of twigs, weed stems, grass and sometimes animal hair or feathers in a natural hollow, an old woodpecker hole, in crevices in rocks, and holes in the sides of buildings. Many nest boxes have been erected to support these and other bluebirds.
Typically 4-6 pale blue eggs are deposited. The female incubates them for about two weeks and hatchlings are ready to leave the nest in another three weeks. The young are cared for by the parents for another 3-4 weeks. Mountain Bluebirds often have two broods per year (Kaufman).

Kestrel-like Hovering

The diet of the Mountain Bluebird consists primarily of insects including beetles, grasshoppers, caterpillars, crickets, ants and bees (Kaufman). Foraging usually begins from a perch such as a fence, low branch, or rock. Frequently the Mountain Bluebird will hover in place as if to inspect an area before dropping to capture prey, in a manner that is very similar to a hunting American Kestrel. At other times it will attempt flycatching and hawking insects in flight (Power and Lombardo). You can see a video of a male Mountain Bluebird bringing food to a nest box at the Macaulay Library.

Mountain Bluebirds are migratory along the Pacific Flyway and breeding birds will arrive in Washington in late March or early April. However, many Mountain Bluebirds breed farther north and will be observed as migrants passing through the state. They begin southward migration in September as they gather in family flocks and later join larger flocks of a hundred or more on their way south. Many will associate with Western Bluebirds and sparrows in mixed migratory flocks (Power and Lombardo).
The Mountain Bluebird is in the genus Sialia, Greek for a bird, and shares it with the Western (S. Mexicana) and Eastern Bluebirds (S. sialis). There are no large-scale conservation measures in place and the population is considered stable or expanding. Breeding has been supported by human activities such as controlled burns and the introduction of nest boxes, which Mountain Bluebirds use more than other bluebirds. It is a species of least concern on the International Union for Conservation of Nature Red List.