Eastern Bluebird Natural History

The Eastern Bluebird (Sialia sialis) is a small, charming, charismatic songbird in the Thrush family, which includes other common birds such as the American Robin (Turdus migratorius), Wood Thrush (Hylocichla mustelina), and Veery (Catharus fuscescens). Males are easily identifiable with their strikingly vivid, deep royal blue plumage above, rusty orange/red chest, and white belly. Females are paler overall with a grayish/blue coloration above and subdued rusty orange/brown chest.

Eastern Bluebirds prefer open habitats that have trees or nest boxes to provide cavities for nesting, but do not have a dominant shrub understory. Ideal habitats include open woodlands, meadows, prairies, and orchards. In Ohio, they can be found any time of the year. Although many migrate south for the winter, some will stick around and gather in large flocks. Flocking together is advantageous because singular birds do not have to work as hard searching for food, water, and shelter, as well as avoiding predators during harsh conditions. Eastern Bluebirds are secondary cavity nesters, meaning they are not capable of creating their own cavities, so they rely on other animals such as woodpeckers and other natural events to create cavities for them.

In the early 1900's, Bluebirds were one of Ohio's most commonly encountered rural birds. Then, between 1920 and 1970, Bluebird populations dwindled to alarmingly low numbers. A bird that once was so common became a rare sight to behold. There were many contributing factors, particularly imprudent anthropogenic events along with a series of severe winters, resulting in a population decline of up to 90%. Extensive land clearing for agriculture and expansive housing development due to the ever increasing urban sprawl into rural areas led to a decrease in trees and open areas resulting in a decrease in natural cavities and ideal habitat. Over time, wooden fence posts that used to provide cavities for Bluebirds and other cavity nesting species alike were replaced with metal posts. The introduction of herbicides and pesticides, forest management techniques/philosophies (removing dead trees/snags), and the increase in feral cat populations also all were significant factors that contributed to Bluebird population declines.

However, the biggest detriment to Bluebird population decline can be attributed to the introduction of two non-native bird species: House Sparrows (Passer domesticus) and European Starlings (Sturnus vulgaris). Both House Sparrows and European Starlings are cavity nesters and both species are highly adaptable, aggressive birds. These non-native birds outcompete native species for space. House Sparrows are small enough to fit into any size cavity that a Bluebird can, and they will always chase and attempt to kill young and adults. Starlings are larger than Bluebirds. When the right precautions are taken during the installation of artificial nest boxes for Bluebirds, ensuring the entrance hole is just the right size, Starlings can be deterred from intervening. Natural cavities present more opportunities for these non-native species to harass Bluebirds because Woodpeckers tend to create large cavities. 

There are many different designs that can be used to build your nest box. "One board" nest boxes are one of the easiest designs to construct and clean. A blueprint with step-by-step instructions can be found here. Bald Cypress, Pine, or Eastern Red Cedar are some of the best wood materials to use for building nest boxes.

It is important to follow these basic steps when deciding where to install your Bluebird Nest Box:

• Place your nest box in optimal habitat to attract Bluebirds
• Install boxes at least 100 yards apart
• Keep the box at least five feet off of the ground
• Make sure to install a baffle to deter predators
• Position your nest box with the entrance hole facing north, east, or north-east

- This avoids direct sun exposure, which runs a risk of overheating the nest box

More Info Coming Soon...