Return of Bird of the Week: Mountain Bluebird


Mountain Bluebird Male, Bennett Mountains, Idaho

A final thrush before we move on to a different family of birds, and WC has saved one of the best for last. The state bird of Idaho – it’s available as an alternate license plate – as well as Nevada, the Mountain Bluebird’s electric blue coloration is always a delight. Which is probably why WC has just under a thousand photos of the species. And would happily take a thousand more.

Despite that exquisite color, Mountain Bluebirds are the hardiest of the Sialia bluebirds, breeding as far north as central Alaska and the Yukon Territory, all the way south to Northern Arizona. In more southerly latitudes, they are mostly found in the mountains that give them their name, but on their wintering grounds they are often lowland species.

They are secondary cavity nesters, using cavities excavated earlier by woodpeckers. That cavity requirement may explain why they are usually one of the first migrants to arrive in their breeding range, an evolved technique to get the choice cavities before other species arrive. Humans’ decision to build nest boxes, which Mountain Bluebird are happy to use, may be a kind of penance for introducing Eurasian Starlings and House Sparrows into Mountain Bluebirds’ range. The aliens compete with the bluebirds for nesting cavities.

Mountain Bluebird Female, Bennett Mountains, Idaho

Mountain Bluebirds are sexually dimorphic. In contrast to the near uniform blue body of the male, the female is grayish brown on the head and upper back, sometimes flecked with or tinged a light cerulean blue. The rump stands out as a patch of light cerulean. And the scapular, primary, and tail feathers are mostly a light cerulean blue. The wing coverts are largely grayish brown with distinct white edges. Females also have a modest white eye-ring. It’s a subtler beauty than the arresting blue of the males, but still very attractive.

Usually Mountain Bluebirds wait for slightly warmer weather before laying eggs. Clutch size ranges from 6-8 eggs. Only the female incubates the eggs, but the male feeds the female on eggs. Incubation lasts 12-16 days, longer in cooler environments. The hatchlings are brooded for about seven days. The young birds fledge after about 21 days. The parents continue to feed and care for the young for as long as three weeks after fledging. Double clutches are common in the southern half of Mountain Bluebirds’ range.

Mountain Bluebird Juvenile, McCall, Idaho

About two-thirds of Mountain Bluebirds survive from egg to independent fledgling. The oldest observed bird was nine years old; the average survival is about 5.5 years among birds reaching maturity.

The estimated population is 6 million birds. After a 20% decline from 1968-2015, populations appear to have stabilized, possibly as a consequence of the various Mountain Bluebird nest box programs, including the Larson Bluebird Trail.

Mountain Blue Bird male, worn plumage, Camas Prairie, Idaho

As a result of the comparatively stable population, wide breeding and winter ranges and recent breeding successes in the nest boxes, IUCN classifies Mountain Bluebird as a species of Least Concern.

For more bird photographs, please visit WC’s bird photo site, Frozen Feather Images