In the past the Eastern Bluebird, Sialia sialis, population has been on the decline. This has been attributed to the introduction of invasive species such as the house sparrow and the loss of suitable habitat. Currently, their population is on the rise and estimated to be more than 20 million strong (Eastern Bluebird). This positive turn in their population trend is largely due to efforts made by conservation minded individuals and organizations. In order to properly manage bluebirds, there is some information that will prove valuable in your efforts.
Eastern Bluebirds prefer open areas such as pastures and clearings that are surrounded by timber. This allows them access to their hunting grounds as they primarily feed on the insects found in these open areas. Timbered areas are necessary as bluebirds are a cavity nesting species, inhabiting old wood pecker hollows and other such cavities found within trees.
The nesting season ranges from February - July (The Texas Breeding Bird Atlas). They will lay multiple eggs, typically 4-7, that are pale blue. On rare occasions their eggs can be white. Incubation is approximately 15 days, after which fledglings will stay in the nest for about 18 days. A breeding pair will produce 2-3 broods per year (Eastern Bluebird - Audubon).
Using this information, we can make some determinations on the best way to make improvements for the species. The quickest way to provide supplemental nesting opportunities for the bluebird is through the installment of nesting boxes. Nesting boxes should be made from wood, preferably from species that will withstand the elements well: cedar, cypress, redwood. They should be unpainted, as the raw wood finish will best replicate the natural cavities in which bluebirds take up residence. The optimum entrance hole will be 1.5 inches in diameter as this will reduce predation while allowing ease of entrance for the bluebird. Lastly, the box should be built in a way that allows it to be opened for easy cleaning.
The nesting box should be installed with the entrance facing east, as this will help with temperature regulation. The entrance should also be facing an open area that provides them forage opportunities. Nesting boxes should also be installed in close proximity to a timbered area where they would naturally find cavities. Most boxes are mounted on a pole (landscape timber, T-post, fence post) at a height of at least 6 feet. The pole should be outfitted with a baffle to provide additional protection from predators.
Routine maintenance is crucial to the continuing success of your nesting boxes. Over time, boxes will accumulate residual waste, old nesting materials, and become a home for wasps and ants. The buildup of waste/debris can contribute to the spread of diseases and parasites from one breeding pair to another. As such, it is important that waste is removed and the box decontaminated through the use of non-toxic cleaners such as thymol oil. A proper box maintenance kit should include a scraper, brush, cleaning solution, and tools to make minor repairs such as a screwdriver and additional screws.
Cleaning your boxes is also the perfect opportunity to monitor the brood patterns of your local bird populations. Creating records of which boxes are being utilized and making egg counts can be valuable in the future when making management decisions. Egg counts can also be listed as a qualifying wildlife management practice if you are seeking a 1-d-1 wildlife management exemption.
If you have installed nesting boxes on your property it is likely that undesirable species will eventually take up residence in some of them. The most likely culprits will be house sparrows and European starlings. These species compete directly with the native bluebirds. They will destroy bluebird eggs and kill the adults inside. They also compete through their habitation of suitable nesting cavities, both natural and artificial.
Invasive species can be legally eradicated in most jurisdictions by a variety of methods. When checking the nesting boxes, it is important that the nests of these birds be removed and their eggs destroyed. A house sparrow has a distinct nest that resembles an upside down stocking. The nest will be built up to the entrance hole with a tunnel leading down to the eggs. The eggs of a house sparrow will typically be white with gray flecks. There are also traps available such as the Van Ert trap which you can find at https://vanerttraps.com/. These traps must be installed in a bluebird nesting box as they are intended to capture invasives that will utilize the boxes. They must be monitored daily while the trap is activated in order to prevent accidental kills of desirable species.
A Continual Effort
As the landscape is continually “beautified” and cavity providing trees are removed, it is important that landowners remain diligent in their efforts to promote conservation of the Eastern Bluebird. The species will only continue to face hardship as habitat is destroyed, invasive species increase in number, and dead standing trees are removed due to safety or aesthetic reasons. Despite the odds, the Eastern Bluebird has bounced back and is enjoying a much stronger population than that of previous decades.
"Eastern Bluebird." American Bird Conservancy. 21 Apr. 2021. Web. 17 May 2021.
"The Texas Breeding Bird Atlas." The Texas Breeding Bird Atlas. Web. 17 May 2021.
"Eastern Bluebird." Audubon. 30 Apr. 2020. Web. 17 May 2021.
Written by: Jacob Gaskamp
Publish date: 06/07/2021