This video from the USA says about itself:
26 May 2013
This film is condensed from about a three hour fledging experience of Western Bluebirds being coaxed from their nest box. Both parents are seen feeding the nestlings but in between the feedings they perch nearby, sometimes with food and sometimes not, and try to coax the nestlings to leave the safety of the only home they know. You will hear the parents call to the nestlings and see they nestlings chirping back. You will also hear many other bird species in the background including Ash-throated Flycatcher, California Quail, Mourning Dove and Acorn Woodpecker.
There were also Violet-green Swallows checking out the nest cavity before the first nestling ever fledged. Once it leaves the nest, you will see the young bluebird perching for the first time in a nearby oak tree, the second nestling soon to follow. I watched three of the five nestlings fledge but had to leave before the last two left the nest box.
From the Cornell Lab of Ornithology in the USA:
Nest Box Occupancy Indicates Good Habitat Quality in California
The state motto of California is “Eureka! I have found it!” Perhaps that’s what a Western Bluebird thinks when it finds that perfect nest box in a good habitat. New research from the Cornell Lab of Ornithology, conducted in California’s oak woodlands, reveals that five species of cavity-nesting birds—Western Bluebird, House Wren, Oak Titmouse, Ash-throated Flycatcher, and Violet-green Swallow—divvy up the nesting habitat according to their specific vegetation preferences and, in the process, improve nesting success.
The researchers found that nest box occupancy rates were a good indicator of nesting success, which has management implications for the declining Oak Titmouse population. This work furthers our understanding of habitat preferences and the role that humans can play in the distribution of nest boxes. Read a brief summary of the research here.