Blue bird houses

Bluebirds are territorial, prefer open grassland with scattered trees and are cavity nesters. Bluebirds can typically produce between two and four broods during the spring and summer (March through August). Males identify potential nest sites and try to attract prospective female mates to those nesting sites with special behaviors that include singing and flapping wings, and then placing some material in a nesting box or cavity. If the female accepts the male and the nesting site, she alone builds the nest and incubates the eggs. Ladies does that sound familiar.
Predators of young bluebirds in the nests can include snakes, cats and raccoons. Non-native and native bird species competing with bluebirds for nesting locations include the Common Starling, American Crow, and House Sparrow, which take over the nesting sites of bluebirds, killing young and smashing eggs and probably killing adult bluebirds.
Bluebirds are attracted to platform bird feeders, filled with grubs of the darkling beetle, sold by many online bird product wholesalers as mealworms. Bluebirds will also eat raisins soaked in water.
By the 1970s, bluebird numbers had declined by estimates ranging to 70% due to unsuccessful competition with house sparrows and starlings, both introduced species, for nesting cavities, coupled with a decline in habitat.
Of all the birds a gardener could choose to attract, the bluebird is the quintessential helpful garden bird. Gardeners go to extreme lengths to attract and keep them in the garden for their beneficial properties. Bluebirds are voracious insect consumers, quickly ridding a garden of insect pests.

I just finished cleaning out the old nests in my two bluebird houses.  Hopefully there are several males that are successful in attaching females to build  nests this year.  When I moved back to Bemidji and purchased my house, I knew nothing about care of the nest or bluebird habits.  I found that it is easy.