There are three distinct species of bluebirds in North America — Eastern, Western and Mountain — but only Eastern Bluebird, Sialia sialis, is a year-round resident and breeder in Florida. Bluebirds are insect eaters with small bills and naturally breed in established holes in trees, posts and poles. When homeowners and road crews remove dead and rotting trees, suitable nesting cavities become rarer. Eastern Bluebirds have adapted to nesting in human-made cavity nest boxes and are often seen perched on utility lines and fences along roadsides where they can readily spot insects in the grassy, mowed green spaces below.
Bright and beautiful bluebirds are in the thrush family in the order Passerine with other perching bird species. Eastern Bluebird is the state bird of Missouri and New York and expanded its range westward as settlers planted more trees in grasslands and dedicated homeowners provided nest boxes. It now ranges west of the Rocky Mountains from southeast Saskatchewan to Nova Scotia in southern Canada, south through the central and eastern U.S., and through Mexico as far south as Nicaragua in Central America.
American Robin, Tardus migratorius, is also a widespread perching thrush that breeds in northwestern Florida. It prefers an open but covered shelf platform to build a nest on. The flocks of American Robins seen in the rest of Florida are winter migrants that fly north to breed. Although Robins are commonly seen pulling earthworms from mowed spaces, they devour berries and insects too.
A third thrush species, Hermit Thrush, Catharus guttatus, is a winter resident throughout Florida and the Southeastern Coastal Plain. Five other thrush species pass through Florida during spring and fall migration. These migrants are the uncommon Gray-cheeked Thrush; the rare Bicknell’s Thrush close to the east coast; the fairly common Veery, which winters in South America; Wood Thrush, common in deciduous and mixed woods; and Swainson’s Thrush, a trans-Gulf migrant that winters in Central and South America. Wood Thrush breeds in north and northwest Florida
As flying squirrels have generally finished raising babies in cavity nest boxes by mid-February, now is the time to clean out old nest boxes, repair as needed and paint the outside to protect the wood and reflect sunlight. Use a light color.
Do not paint the insides or around the entry hole. To attract Eastern Bluebirds, nest boxes need to be at least 85 feet apart with a clear flight path and preferable over a mowed space (lawn) where there are insects. I recently planted eight boxes on steel poles along 660 feet of roadside fronting my property. Bluebirds perch on the overhead powerlines on my side of the limestone country road.
Below each nest box, I drilled a hole through the conduit pipe and slid a repurposed, clear juice bottle up the pipe, then put a long deck screw through the hole. The dangling bottle prevents predators like snakes and raccoons from climbing the smooth pipes. The last bottles discolored and went opaque after eight years in the hot Florida sunshine but did not harden, fracture of disintegrate.
Locally native cherry, redbud and plum trees have blossommed and new spring leaves have emerged. Tent caterpillars, Malacosoma americanum, emerge from their egg mass and build a protective tent for protection from predators. The caterpillars eat new leaves but do no serious harm to the hardwood tree hosts. However, tent caterpillars are a readily available food source for hatchling Eastern Bluebirds and other nestling species in the garden. After about six weeks of eating and growing bigger, any surviving tent caterpillars spin a cocoon, usually inside the tent, and pupate. After another two weeks, adult moths emerge to mate and repeat the life cycle, creating a sustainable source of bird food for second and third clutches of bluebird nestlings.
Bluebirds prefer a 6 x 6 inch floor size and a round 1.5 inch entry hole that is 9 inches above the floor. The roof should be sloped so rain and predators like feral cats and raccoons slide off and are not able to reach inside the entry hole. Vent holes — high in the sides but well covered by the roof — let out hot air to keep hatchlings cooler.
Smaller floor size and shorter nest boxes will attract Carolina Chickadees, Downy Woodpeckers and Tufted Titmice. Larger boxes may be used by Great-crested Flycatchers and Red-bellied Woodpeckers. Woodpeckers often peck and enlarge the entry hole. If that happens, fasten a 3 x 3 inch piece of wood with a 1.5” hole in it over the enlarged hole. The extra thickness will deter predators from reaching inside to snatch the babies.
Jane Weber is a professional gardener and consultant. Semi-retired, she grows thousands of native plants. Contact her at firstname.lastname@example.org or phone 352-249-6899.