Grass, twigs and moss and other materials suitable for a nest.
Some Bluebirds come from their Hushabye Mountain winter nesting grounds.
Bluebirds and woodpeckers exhibit a symbiotic relationship primarily through the use of nesting sites. Woodpeckers create cavities in trees for their nests, which can later be used by bluebirds for shelter and breeding. This relationship benefits bluebirds by providing them with safe nesting locations, while woodpeckers benefit from the activity of bluebirds, which can help deter potential predators around their nesting sites. Overall, both species gain advantages from their interactions, showcasing a mutualistic aspect of their relationship.
Generally house sparrows and house wrens. Both are cavity nesters and will compete with bluebirds for nesting spots.
Many died in communal roosts during winter nesting in areas where carbon monoxide was present. Clearing of dead trees removed nesting places. Now, bird nesting boxes have expanded by people, and bluebirds have returned to former numbers.
Sometimes bluebirds face competition with other birds over nesting sites. Another problem bluebirds have is a lack of natural habitat. In areas that are more developed there are less natural cavities for them to nest in.
By protected habitat areas, and by providing nesting boxes.
Probably because your home as everything they need to survive and make nests. If you want to get rid you them take down a birdhouse or two as bluebirds like nesting in birdhouse.
They may have moved to a different nesting site. Also they may have not had enough fresh food/water.
Bluebirds do sometimes just go in half way. They may be arranging nesting materials or doing something else. Entrance holes for bluebirds should be 1.5 inches.
Bluebird have adapted to use man made boxes for nesting. Their ready acceptance of the man made home has lead to a very successful conservation effort.
The bluebird's favorite flower is often considered to be the bluebell, as its vibrant blue color attracts these birds. Bluebirds are also drawn to flowering plants that provide insects for food and nesting materials. Additionally, native wildflowers that bloom in open fields can create a suitable habitat for bluebirds.
You can put nest boxes out with bird feeders and hay. The birds will feel safe within a nest box.