Mountain bluebirds 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 monogamous. After the couple decides together on an ideal nesting site, the female will typically build their nest themselves out of thin, dry material from the surrounding landscape while the male protects the area, defending against unwelcome visitors. It is true, though, that both males and females fiercely protect the nest. Once the nest is built, the female will lay an egg a day. Eggs are pale blue and unmarked, sometimes white. The clutch size is four or five eggs and she will incubate them for about two weeks. Young are naked and helpless at hatching and may have some down. The young will usually take about 21 days before they leave the nest, and it can take up to two months to raise fledglings to a stage of development at which they are able to fend and provide for themselves.