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The Mountain Bluebird (Sialia currucoides) is a medium-sized bird weighing about 30 g (1.1 oz) with a length from 16–20 cm (6.3–7.9 in). They have light underbellies and black eyes. Adult males have thin bills that are bright turquoise-blue and somewhat lighter beneath. Adult females have duller blue wings and tail, grey breast, grey crown, throat and back. In fresh fall plumage, the female's throat and breast are tinged with red-orange; brownish near the flank contrasting with white tail underparts. Their call is a thin few; while their song is warbled high chur chur.
These birds hover over the ground and fly down to catch insects, also flying from a perch to catch them. They mainly eat insects and berries. They may forage in flocks in winter, when they mainly eat grasshoppers. Mountain Bluebirds will come to a platform feeder with live meal worms, berries, or peanuts.
Their breeding habitat is open country across western North America, including mountain areas, as far north as Alaska. They nest in pre-existing cavities or in nest boxes. In remote areas, these birds are less affected by competition for natural nesting locations than other bluebirds. Mountain Bluebirds are a monogamous breed. The male can be seen singing from bare branches. The singing takes place right at dawn, just when the sun rises. Females usually build the nests themselves. Eggs are pale blue and unmarked, sometimes white. The clutch size is 4–5 eggs. Young are naked and helpless at hatching and may have some down. Incubation normally last 14 days and the young will take about 21 days before they leave the nest. Both males and females fiercely protect the nest.
Mountain Bluebirds are cavity nesters and can become very partial to a nest box, especially if they have successfully raised a clutch. They may even re-use the same nest, though not always. Providing nest boxes is a great way to observe these beautiful birds. Mountain Bluebirds will not abandon a nest if human activity is detected close by or at the nest. Because of this, Mountain Bluebirds can be easily banded while they are still in the nest.
- All About Birds: Mountain Bluebird, Cornell Lab of Ornithology
- The Condor, Vol. 83, No. 3 (Aug., 1981), pp. 252–255