The number of bluebirds is increasing, thanks to birdwatching groups, bird societies and individuals who share the desire to protect this bird. Once on the decline as a result of habitat loss and other competing bird species, bluebirds are now seen in abundance in rural and suburban gardens. .
Bluebirds will generally begin their nesting season in March and continue through August. Nesting may occasionally begin as early as February or as late as the end of April for some bluebirds, especially the first-timers.
When building their nest, bluebirds tend to stick to clean materials found in nature. Examples include pine needles, hay, straw, plant fibers and grasses. The nest is lined with bits of hair, fur or feathers. Bluebirds don't use junk as material, and if you notice a nest containing strings, sticks, cigarette butts or other debris, it's likely that the nest belongs to a different species.
Bluebirds are cavity nesters and will seek out birdhouses or abandoned woodpecker holes in trees or poles to build their nest. They're not very selective with height and will use holes or birdhouses anywhere from 3 to 20 feet from the ground. When installing a birdhouse for bluebirds it's best for it to be a minimum of 5 feet above the ground to discourage predators from attacking the nest.
Once the male and female have chosen a location, they work together to construct the nest. It takes an average of 11 days to build the nest. Once it's complete, and the eggs are laid, the incubation period is anywhere from 13 to 16 days.