During the breeding season, they build their nests in cavities, such as holes in trees, birdhouses, or natural crevices in cliffs. Mountain bluebirds are known for their preference for open habitats and will often build their nests in areas with a clear view of their surroundings. The female bird is responsible for building the nest using materials such as grass, moss, and feathers. Once the nest is complete, the female will lay a clutch of 4-6 small blue eggs, which she will incubate for about 12-14 days. Both parents will help feed the chicks, which will leave the nest about three weeks after hatching. Mountain bluebirds are known for their strong family bonds and will often return to the same nesting site from year to year.

Tree swallows are known for their strong nesting habits and will fiercely defend their nests from predators and competitors. The female bird typically builds the nest using soft materials such as feathers and grass, while the male bird helps to gather materials and protect the nest site. Once the nest is complete, the female will lay a clutch of 4-7 small white eggs, which both parents will take turns incubating. After the eggs hatch, both parents will work together to feed and care for the young until they are ready to leave the nest and fledge.

Chickadees are known for their ability to excavate their own nesting holes, although they will also use natural cavities or birdhouses if they are available. The female black-capped chickadee builds the nest using soft materials such as moss, grass, and feathers, and she lines the nest with hair and feathers to keep the eggs warm. Once the nest is complete, the female will lay a clutch of 6-8 eggs, which she will incubate for about 12-13 days. Both parents will help feed the chicks, which will leave the nest about two weeks after hatching. Chickadees are known for their strong family bonds and will often reuse the same nesting site from year to year.

House wrens are small birds that are found throughout North and Central America. They are known for their active and energetic behavior, as well as their complex and interesting nesting habits. During the breeding season, house wrens build multiple nests in a variety of locations, such as cavities in trees, birdhouses, or even hanging baskets. The female bird is responsible for building the nests using materials such as grass, moss, twigs, and feathers. Once the nests are complete, the female will lay a clutch of 5-8 eggs in each nest. Although both parents will help care for the chicks, the female will do the majority of the incubating and feeding. After the chicks have fledged, the male and female will continue to feed them until they are able to care for themselves. House wrens are known for their territorial behavior and will fiercely defend their nests from predators and competitors.

The House Sparrow is a small bird that is native to Europe and Asia but has been introduced as an invasive species in several countries including the United States. These birds are known for their adaptability and ability to thrive in a variety of habitats, including urban areas. During the breeding season, House Sparrows build their nests in cavities, such as holes in trees, birdhouses, and even in buildings. The female bird is responsible for building the nest using materials such as grass, feathers, and twigs. Once the nest is complete, the female will lay a clutch of 4-7 eggs, which she will incubate for about 12-14 days. Both parents will help feed the chicks, which will leave the nest about three weeks after hatching. As an invasive species, House Sparrows can have negative impacts on native bird populations by competing for resources such as food and nesting sites. This highlights the importance of monitoring and managing invasive species to ensure that they do not cause harm to the ecosystems in which they are introduced.

Northern flying squirrels are small, nocturnal mammals that are native to North America. They are known for their ability to glide through the air using a membrane of skin that extends between their front and hind legs. In some cases, northern flying squirrels have been known to use bluebird nesting boxes as a place to sleep and stay warm during the winter months. This can pose a problem for bluebirds, as the squirrels can occupy the boxes and make it difficult for bluebirds to find suitable places to build their nests. To prevent this, bluebird nesting boxes should be designed with baffles or other deterrents to keep flying squirrels out. Alternatively, nest boxes specifically designed for flying squirrels can be provided in nearby trees to give the squirrels a place to sleep while protecting bluebird nesting boxes. This can help to conserve populations of both bluebirds and flying squirrels by providing suitable habitat for each species.