Mountain Bluebird

Overview

The Mountain Bluebird (Sialia currucoides) is a dazzling Medium-sized thrush that acts as a symbol of the vast, open spaces of western North America. Often described as a 'breath of sky' on the wing, this species is highly regarded by birdwatchers for its vibrant turquoise plumage. While it shares its nesting habits with other bluebird species, the Mountain Bluebird is uniquely adapted to high-altitude and rugged landscapes, often breeding in subalpine and alpine zones well above the range of its counterparts.

Breeding populations are highly migratory, navigating elevations as much as geographic coordinates to find optimal weather and food sources. Because they rely heavily on pre-existing cavities for nesting, they are a primary beneficiary of community nest-box trails across western pastures and open lands.

Identification

Identifying the Mountain Bluebird is relatively straightforward due to its distinctive coloration and structural profile, which sets it apart from related bluebird species.

• Adult Males: Draped in a brilliant, uniform sky-blue or cerulean color. Unlike the Eastern and Western Bluebirds, the male Mountain Bluebird has no warm rufous or orange breast; its plumage transitions from deep turquoise-blue on the back and head to a lighter, soft blue on the breast, fading into a clean white belly.
• Adult Females: Subdued and elegant, mostly grayish-brown above with soft washings of pale blue on the wings, tail, and rump. The breast is a dull buffy-grey, occasionally showing a very faint orange tint, but lacks the rich rust color of other female bluebirds. They also have a white eye-ring.
• Shape and Structure: Compared to other bluebirds, this species has longer wings and a more slender, slightly longer bill. Their silhouette when perched is upright and long-winged, giving them a sleek, elegant appearance.
• Similar Species: The lack of any reddish-orange plumage on the breast is the primary field mark distinguishing male Mountain Bluebirds from both Western Bluebirds and Eastern Bluebirds. Female Mountain Bluebirds are distinguished from other female bluebirds by their overall paler, greyer appearance, longer wingtips, and lack of conspicuous orange on the breast.

Habitat and Range

Breeding Habitat

During the spring and summer breeding seasons, Mountain Bluebirds occupy open country. They are commonly found in pastures, rangelands, clear-cuts, sagebrush flats, and high-altitude alpine meadows up to 12,000 feet. They require open terrain with low ground cover to hunt effectively, alongside scattered trees, snags, or fence posts for nesting and perching.

Range and Migration

While breeding occurs throughout western North America, extending from Alaska and western Canada down through the mountainous western United States, they migrate south to winter in the southwestern United States and Mexico. They are altitudinal migrants, moving down to low-elevation grasslands, brushy deserts, and agricultural fields once snow covers their high-altitude breeding grounds.

Behavior and Ecology

Foraging and Diet

During the breeding season, Mountain Bluebirds are exclusively insectivorous. They employ a specialized hunting technique rarely seen in other bluebird species: hover-foraging. They can hover stationary in mid-air over grasslands (similar to a small American Kestrel) before dropping down to the ground to capture beetles, grasshoppers, caterpillars, and spiders. In transition periods and during winter, they switch to eating small berries, particularly juniper berries, mistletoe, and elderberries.

Vocalizations

They are generally quiet birds. The song is a soft, clear, warbling series of notes delivered at dawn by the male, which sounds like 'tew' or 'chur-chur.' Their call is a simple, thin, high-pitched 'phew' or 'tew' sound, often emitted when in flight or when disturbed near the nest.

Nesting and Reproduction

As secondary cavity nesters, they cannot excavate their own nesting holes. Instead, they rely heavily on old woodpecker cavities, natural tree hollows, and crevices in sandstone cliffs and clay banks. They have also adapted exceptionally well to wooden nest boxes. The female constructs a loose cup nest of dry grass, pine needles, and bark strips, laying a clutch of 4 to 8 pale blue (or occasionally white) eggs, which she incubates for approximately 13 to 14 days.