Western Bluebird

Sialia mexicana

The Male Western Bluebird, his head, throat and upperparts bright, are a deep cobalt blue. Breast chestnut. Blue on belly and undertail coverts.

Varying amounts of chestnut on back. Eyes are dark and legs are dark.

Female Bluebirds are duller and not extensively blue. Head and throat gray. Back gray-brown. Abdomen and undertail coverts grayish. Blue wings and tail. Chest duller chestnut.

Juveniles have a spotted chest and back, blue in wings and tail.

Immature are similar to adults, but duller.

Western Bluebird

Length: 6.3–7.5 in (16–19 cm)

Weight: 0.8–1.1 oz (24–31 g)


The Western Bluebird is a common sight in parklands of the West. Unlike the other species of bluebirds, it does not like large meadows, preferring open forests instead.

These Bluebirds are found in open coniferous forests, farmlands, and steppe habitats, often at the edges where the forest meets the steppe zone. Forest openings and clearings and agricultural areas are also good habitat for the Western Bluebird.

In winter, they inhabit a wider variety of open and semi-open terrain, especially piñon-juniper forests, farmlands, and deserts.


Western Bluebirds are often seen perching alone on fence wires, posts, snags, or tree branches by open meadows, pouncing on the ground to catch insects. They also fly out to catch aerial prey and grab insects from twigs and leaves.


In summer, Bluebirds eat primarily insects. In winter, berries and small fruits become more important parts of the diet, with mistletoe, juniper, and elderberry all important food items.


The male arrives on the breeding grounds before the female, and defends the nesting territory by singing. They are cavity-nesters, finding a natural hollow in a tree, an old woodpecker hole, a hole in a building, or a man-made nest box. Preferred nest-holes are fairly low, less than 50 feet from the ground.

The female builds the nest, although the male may help. The nest is a loose cup of twigs and weeds, lined with finer plant materials. The female incubates the 4 to 6 eggs, while the male brings her food.

Once the eggs hatch, she broods the young while he continues to bring food.

Western Bluebird

They both feed the young, which fledge at 2 to 3 weeks, The adults then have a second brood.

Genetic studies showed that 45% of nests had young that were not fathered by the defending male, and that 19% of all the young were fathered outside the pair bond.


The Western Bluebird is the least migratory of the bluebirds, and much of its migration is alatitudinal rather than latitudinal. Some bluebirds migrate south in the fall to locations throughout the southwestern United States and central Mexico.

Small flocks occasionally remain through the winter in valleys, especially in mild winters. Most of the population retreats to lower elevations in the winter. On both sides of the mountains, the winter range varies with food sources. In any case, they are very uncommon in winter.


In recent decades, bluebirds have declined over much of its range. This decline is well documented and is attributed to a combination of competition with House Sparrows and European Starlings for nesting cavities, a reduction of natural cavities.

An intense nest box program has helped the population to rebound, and helped with the re-establishment of breeding pairs where Bluebirds once were present.

Eastern Bluebird

Mountain Bluebird

Western Bluebird and other Backyard Birds

Nest Boxes

Create a Bird Garden

Birds, Butterflies, Gardens and more. For your weekly 'Gardening For Wildlife' newsletter, sign up below.

Enter your E-mail Address
Enter your First Name (optional)

Don't worry — your e-mail address is totally secure.
I promise to use it only to send you Gardening For Wildlife.