The Mountain Bluebird Nesting Preferences
Mountain bluebirds are solitary nesters although they do know how to make do with another bird nest nearby when there is a lack of nesting site elsewhere. They make nests in cavities, whether natural or man-made. Cavities most often used are woodpecker holes, cliff holes, dirt banks, old swallow nests and nest boxes. Nest building usually takes several days up to a little more over a week to be finished. Popular nesting materials include stems, grass, weed stems, pine needles, rootlets, bark, lined with softer materials like wool, hair, or feathers and twigs.
One of the unusual things about Mountain Bluebirds is that they are known for reusing old nesting sites. They not only reuse it simply to raise the second batch of brood during the same breeding season but even do so during the next breeding season(s). This behavior is especially true for Mountain bluebird pairs that were able to raise a brood successfully in the nesting site. Even more interesting is that they do not only get attached to a specific nesting site but to the specific kind of nesting box they used. Though they do not always reuse the very same nest they have a tendency of choosing nesting boxes that were similar if not identical to the box they previously used. First time breeders also showed this bias for previously used nesting boxes by choosing nesting boxes that are identical to the nesting boxes wherein they were hatched and raised. Note though that observations to this end were on mountain bluebirds that used nesting boxes and not natural cavities.
Nest building starts during the beginning of breeding season. Breeding season start in April on the southern parts of the mountain bluebirds range and begins in late May on the northern parts of the birds range. It is the female mountain bluebird bird that chooses the nesting site and builds the nest. Throughout the entire process the male also keeps himself busy staying close by to guard the female mountain bluebird. They do help sometimes by bringing some nesting material to the female bird but they do not actually participate in the placement of the material on the nest itself.
Mountain bluebirds that are not successful in their attempt to nest are not easily daunted and simply re-nest during the same breeding season. A pair of mountain bluebirds usually is able to raise two broods each breeding season.