F/11.0, 1/500, ISO 320.
Imagine you are in a water tank with a roof. There are no objects in the tank to help you escape. How do you get out?
Interesting Fact: Males vying over territories chase each other at high speed, sometimes grappling with their feet, pulling at feathers with their beaks, and hitting with their wings. The boxes and tree cavities where bluebirds nest are a hot commodity among birds that require holes for nesting, and male bluebirds will attack other species they deem a threat, including House Sparrows, European Starlings, Tree Swallows, Great Crested Flycatchers, Carolina Chickadees, and Brown-headed Nuthatches, as well as non-cavity nesters such as robins, Blue Jays, mockingbirds, and cowbirds. ( https://www.allaboutbirds.org/guide/Eastern_Bluebird/lifehistory )