Western Bluebird

Sialia mexicana
Western Bluebird
Western bluebirds are members of the Thrush family which also includes mountain bluebirds, American robins and Townsend’s solitaires.  As its name indicates, it is found west of the Rocky Mountains from British Columbia to Mexico.  A portion of Western bluebirds are considered resident throughout their range while others are considered medium-distance migrants who either move to lower elevations or fly south to the American Southwest and Mexico. Although chiefly insect eaters during the breeding season, they will add fruit to their diet in winter which might explain the variety of migratory habitats.   
Associated with forested habitats especially ponderosa pine and aspen, they are found most commonly in open woodlands or at the forest edge.  The western bluebird is one of 29 species of birds on the refuge that nest in cavities in live trees or snags. Bluebirds are considered secondary cavity users since they use natural cavities or those excavated by other species for nesting. This species has experienced dramatic declines in the past as a result of habitat loss through logging and fire suppression and competition for cavities from non-native competitors such as English house sparrows and European starlings.  Bluebirds readily utilize artificial nest boxes which can substitute for natural cavities and be built to exclude non-native competitors.  This characteristic has greatly assisted in the recovery of bluebirds throughout their range.


Both the male and female build the nest which consists of mostly of grass and pine needles in a cavity.  The female lays a clutch of 4-6 eggs over a 5-7 day period.  Eggs are incubated only by the female for 2 weeks. Nestlings are cared for by both the male and female and sometimes other bluebird helpers. Young can leave the nest on average at the age of 19 days.  Once fledged the pair will lay another clutch and depending on the season possibly a third.  Bluebirds are very loyal to a successful nest site often returning to the same box for several years.

Bluebirds are very social and will often congregate in large flocks in September and October. Refuge bluebirds migrate south by mid-November to currently unknown locations but often return to the refuge by mid-February.

The refuge has been monitoring bluebirds with the assistance of many volunteers both through the use of nest boxes and bird counts in aspen and pine forest.  Currently the refuge has 137 nest boxes of which 80% are typically inhabited by bluebirds. Tree swallows, house wrens, white-breasted nuthatches, and black-capped chickadees and northern flying squirrels also use these boxes. Annually the nest boxes have fledged an average of 400 young bluebirds. Our bird counts have shown that as a result of thinning to create more open pine woodlands and the use of prescribed fire that creates snags, bluebirds are increasing in areas of the refuge without the help of nest boxes. Bluebirds are excellent indicators of healthy pine forest.   

Facts About Western Bluebird

Males are brilliant blue with rusty breast, back, and sides

A secondary cavity user commonly found at forest edges and open pine woodlands

May have 2-3 broods in one season

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