Natal down appears on the second day. Eyes begin to open by the fourth or fifth day. Mountain bluebird nestlings are fed by both parents but usually only brooded by the female. In Montana large flocks of mountain bluebirds gather from October to November. In western Montana mountain bluebirds use whitebark pine snags for nest sites at high elevations.
Preferred sites are open or semi-open.
In Wyoming mountain bluebirds used an abandoned American dipper nest on the underside of a bridge. Dead branches are preferred to living ones, presumably for greater prey visibility. Where natural vegetation is tall, mountain bluebirds prefer mowed to unmowed areas. Areas with dry, nonfertile soils, low vegetation, and much bare ground are preferred. In south-central Washington, beetle consumption decreased during the nestling period.