In Colorado, spring does not arrive all at once. It comes in pieces: a warmer afternoon, a longer evening, water where ice used to be. Snow still lingers in the shade of fence lines and north slopes, while exposed ground turns soft and dun under the first mild light. Then a mountain bluebird lands on a fence post or a bare branch above last year’s grass. For a moment it can seem almost too bright for the season, a clean piece of sky set down in the field.

The mountain bluebird, Sialia currucoides, is a small thrush, a little more than 7 inches long. The male is bright blue almost all over, vivid in full sun and powdery in colder light. The female is grayer, with blue in the wings and tail, her color easy to miss until she turns.

It nearly became the state bird in 1931 and, for a time, led the field. The male’s cerulean color fit Colorado’s image of itself: blue sky, clean light, open country. It lost to the striking black lark bunting.

Colorado has three bluebirds – mountain, western and eastern. The mountain bluebird is the one most closely tied to the state’s open country: meadows, foothills, mountain parks, pasture, sage flats, aspen openings and ranchland. It avoids thick cover and does best where the ground stays visible. From a fence post, snag or bare branch, it watches the grass below, then drops and returns to the same perch.

In warm months, mountain bluebirds feed mostly on grasshoppers, caterpillars, beetles and other small prey taken from the ground or caught in short flights. In winter they turn more to berries, especially where fruit hangs on through cold weather.

That pattern is easy to watch. A bluebird sits upright, studies the ground, drops fast, then rises back to the same perch. At times it hovers and dives after prey so neatly that it can look, for a moment, like a tiny kestrel.

Bluebirds are cavity nesters, using holes they did not excavate themselves: old woodpecker hobbits, natural cavities, crevices and nest boxes. In later seasons, bluebirds may return to a cavity or box they used before. In Colorado, nest-box trails and volunteer monitors now shape bluebird nesting from park edges to subdivisions and long stretches of pasture. The birds readily take a box if the surrounding habitat is open.

Bluebirds pair for the breeding season, and it begins at the cavity. The male claims a hole or box and returns to it again and again, singing nearby, pausing at the entrance, then flying back toward the female as if to draw her attention to that single spot. She approaches, studies the opening, goes in, comes out and looks once more. Sometimes she lingers at the lip before slipping inside again, while the male waits nearby, bright against weathered wood or gray wire, then drops to the ground and rises back to the same perch. If she accepts him, the pair is set.

Once she accepts her new home, the season begins in earnest. The female builds the nest, and a clutch of four to eight eggs follows. She incubates while the male stays close. After about two weeks, the eggs hatch, and the traffic starts – insects carried in, waste carried out, both adults working the grass around the nest hole.

From a fence wire or weathered post, an adult drops into the grass and comes back with something pale and soft in its beak, then disappears into the dark opening and is gone again. At the entrance, the young bunch shoulder-to-shoulder, heads lifting at every approach. But a cold snap, hard rain or a run of poor insect hunting can turn that busy nest quiet for the season.

Two to three weeks after hatching, the young leave the cavity, though the feeding doesn’t stop. Their first flights are short and uncertain.

For weeks, the fledglings cling to fence wires, posts and low branches, still calling for food, their wings not quite steady yet. They sidestep along the wire with their mouths open, waiting for one more delivery. If weather holds and insects stay plentiful, the pair may start again.

As summer goes on, those small family groups begin to spread out along fence lines and meadow edges. One bird perches, watches the grass, drops, then rises back to the wire while another follows a few yards off. A young bird misses its footing, regains the strand and tries again.

Another lands in the grass and pops back up to a lower branch, already falling into the pattern. By then, across much of Colorado’s open country, they are part of the landscape – busy, bright and exactly where they belong.