Note: Several readers have requested posts on topics that have already appeared here – this is one of those posts that has been updated and republished.
I think that bluebirds are my favorite wild bird, so I try to do a post each year on creating habitat for them. They live on our farm throughout the year; however, during the warmer months we generally see them around the edges of the farm fields – seldom do they make their way up to the house.
The trees surrounding the farm fields seem to give them an ideal habitat – old tree cavities for nesting and perches perfect for preying on insects in the field. We often see numerous bluebirds of varying ages while we’re out working the field or garden during the spring, summer, and fall.
However, in the winter, the bluebirds spend time around the house, providing us with a treat when we’re stuck inside during cold weather. We don’t see them on the bird feeders, so I don’t think that’s what’s motivating them – I think it may be sources of open water in the house gutters. Whatever, I’m always glad to see them; they seem like such cheerful little birds.
Before the farm, when we still lived in suburbia, we didn’t have ideal habitat for bluebirds, but always tried to provide one because bluebird populations have declined so severely. Up to six pairs of bluebirds will nest per acre and raise multiple clutches per season if proper habitat can be established. We found that understanding their habitat needs and issues is fundamental to building successful bluebird habitat.
Understanding Bluebird Issues
One of the primary causes of decline for bluebirds is lack of nesting cavities. Clearing trees (particularly dead and dying ones) and using metal fence posts removes the cavities bluebirds traditionally used for nests. Their beaks aren’t strong enough to excavate new nests, so they’re totally dependent on finding suitable nesting cavities. House cats have also proven to be lethal predators.
Another cause of decline is competition for the available nesting cavities. When house sparrows and European starlings were imported from Europe, it caused severe competition for available nesting sites. The house sparrows begin nesting very early and often take available cavities first, while the starlings (although they nest later) are so much larger than bluebirds that they forcefully evict nesting bluebirds.
So, placing bluebird nesting boxes in appropriate locations and preventing competition from sparrows and starlings can greatly promote successful bluebird habitat. Preventing starlings is easy, simply make the next box opening 1 ½” in diameter and the starling will be too big to enter the house. For sparrows, it’s necessary to inspect the houses on a regular basis and clean out any sparrow nests before they get established.
Constructing and Placing Bluebird Houses
The bluebird nesting box shown below was designed to meet bluebird requirements, provide easy access for cleaning, and should last many years. One inch thick boards and wood screws should be used for construction, and it’s unnecessary to paint the house. If painting is desired, don’t use dark colors as the house could overheat in hot weather and kill eggs or young birds.
The best places for bluebird houses are reasonably open areas with scattered trees and a good distance from buildings. Bluebirds will not nest in deep woods or shade. Pasture edges, fields, lawns with trees, cemeteries, and golf courses usually make good locations.
Houses should be placed facing south or southeast with a tree located 25 to 100 feet from the front for young birds to use for their first flight. Multiple houses should be spaced 100 yards apart with screening trees or shrubs between the houses. They should be mounted 5 to 7 feet above ground, and a smooth metal pole is better for mounting in areas where cats may be predators. The houses should be in place by February 15 each year.
A bluebird’s diet consists of approximately 80% insects and 20% plants; and should be considered when locating bluebird houses. Common insects are beetles, larvae, caterpillars, grasshoppers, and spiders. Common plants include raspberries, blackberries, and elderberries. All three of these grow naturally and abundantly on Bramblestone Farm and may be one reason we have lots of bluebirds. Bluebirds will eat from bird feeders if they’re stocked with currants, raisins, or other bits of fruit. Bluebird houses should not be placed in any area where insecticides or herbicides are used because this destroys the food supply and may harm the birds.
Once bluebirds have taken up residence, watching the houses and removing nests as soon as young birds have left may increase chances of a second clutch. As a minimum, the houses should be cleaned and repaired in early February each year. Nesting boxes constructed per the directions below and properly located are usually eagerly accepted by bluebirds – we were generally successful in attracting bluebirds even when we lived in the suburbs.