Mountain bluebird

A sky-blue thrush of high, open country, the only bluebird seen regularly above 5,000 feet, nesting in lava-rock crevices at Craters of the Moon.

Mountain bluebird at a glance

Sialia currucoides Sialia currucoides is sy-AL-ee-uh kur-oo-KOY-deez

Type
Bird · songbird
Diet
Insectivore
Size
About as long as a crayon (6.3 to 7.9 inches / 16 to 20 cm), with a wingspan close to a school ruler (12 to 14 inches / 30 to 36 cm) and a weight lighter than a handful of coins (0.8 to 1.3 ounces / 24 to 37 g).
Lifespan
Most live only a few years in the wild; the oldest Mountain Bluebird on record, banded in Alberta, had reached at least 9 years when recaptured.
Conservation
Least concern

Eats insects, tent caterpillars, berries, fruit

In summer it hunts almost entirely by hovering over open ground or shrubs and dropping on insects, including tent caterpillars. In fall and winter, when insects are scarce, it switches to berries and other fruit.

Should you worry?

None. It is a small, harmless insect-eater. It will not bother people, though it can be territorial toward other bluebirds near its nest hole.

Under a flat gray sky along the Loop Road at Craters of the Moon, the bluebird on the sagebrush looks more slate than sky-blue — dull enough that a first glance might write it off as something else entirely. Turn up on a clear day and the same bird reads as pure blue, no gray about it at all.

That’s not a trick of memory. A mountain bluebird carries no blue pigment anywhere in its body. The color comes from the microscopic structure of the feather itself, which scatters light exactly the way the atmosphere does to make the sky look blue — brilliant blue needs bright, direct light to work with, and clouds take that light away. The same bird, the same feathers, and the color changes with the weather. It’s the reason two people describing the “same” bluebird on different afternoons can sound like they saw two different birds.

The lava field gives this particular blue nowhere to hide. Mountain bluebirds nest in cavities, but here there are no trees to speak of — instead they squeeze through openings barely two inches wide into cracks and pockets in the black rock itself, arriving by the flock as early as March and gone again by October. A patch of black lava with a blue bird perched on it, gray or brilliant depending on the clouds, is about as far from camouflage as a bird can get.

Did you know?

  • A mountain bluebird's blue comes from the physical structure of its feathers scattering light, the same optical trick that makes the sky look blue — there is no blue pigment in the feather at all.
  • At Craters of the Moon, large flocks of mountain bluebirds arrive as early as March and leave by October, following the insect supply.
  • It is Idaho's state bird, easy to pick out against the black lava rock at Craters of the Moon.

Common questions

Why do mountain bluebirds look less blue on a cloudy day?

Their blue isn't a pigment — it's tiny feather structures scattering light the way the sky does. Less direct light means less blue to see.

Where do mountain bluebirds nest?

In a cavity — usually a hole in a dead tree, but at Craters of the Moon they squeeze into cracks and pockets in the lava rock itself.

What do mountain bluebirds eat?

Mostly insects, caught by hovering over open ground and dropping down. In fall and winter they eat berries and other fruit instead.

Are mountain bluebirds dangerous to kids?

No. They're small insect-eaters that keep to themselves, though a pair will chase off other bluebirds that get too close to their nest hole.

What eats a mountain bluebird?

Sharp-shinned and Cooper's hawks, falcons, great horned owls, and pet cats catch adults. Raccoons, climbing snakes, chipmunks, squirrels, mice, and weasels raid nests.

Where it lives

Where we got this