A House for the Heavenly — Bluebird Nestbox Basics
(Editor's Note: This article was originally published on May 19, 2008)
I hope you love birds too. It is economical. It saves going to heaven.
— Emily Dickinson
Every bird lover must feel like they are in heaven when they spy a pair of Eastern Bluebirds on or near their property. For those who live in Eastern Bluebird breeding areas, seeing that flash of blue generally is followed by a gasp of delight at the thought of hosting a bluebird pair.
As a participant in the Bird Watching Forum on Dave’s Garden, I quickly learned that THE website for Eastern Bluebird information is Sialis (Sialia sialis is the scientific name for the Eastern Bluebird). If it’s bluebird information you’re looking for, there’s not much you can’t find on this site, including links to other bluebird sites. Also through the forum, I discovered someone I like to call “Mr. Bluebird,” or 2dCousinDave. Dave is an avid bluebirder who gives forum participants daily reports accompanied with stunning photos of his nesting bluebirds. Much of what I have learned about Eastern Bluebirds comes from Dave or one of the other participants who host bluebirds.
As Dave will tell you, hosting a bluebird family is more than putting up a house. It is a serious decision, one that requires a good deal of thought. Because bluebirds face great competition for dwindling nest sites, providing a well-designed and regularly monitored box is extremely important. I strongly recommend spending some time getting to know the Sialis site in order to determine your “bluebird readiness.” If hosting IS for you, your first decision involves a nest box.
The North American Bluebird Society (NABS) approves a number of bluebird houses on the market. To get the NABS approval seal, the box must meet certain criteria designed for the health and safety of the bluebird. If you have chosen to build a house, be sure to check out these specifications from NABS.
Here are the very basics that make up a bluebird house. Adhering to these standards is a must to ensure a healthy habitat.
Materials — Use untreated 3/4" to 1” wood or PVC pipe. If you choose to paint a box, be sure to paint the outside only. To keep the box from overheating, use light-colored paints
Roof — A roof with a 2" to 5” overhang ensures a dry nestbox. Grooves on the top help moisture drain and keep the wood drier. A longer overhang provides more protection from the elements.
Entrance — It’s important to choose the right size entrance hole to deter larger birds from nesting in the box. For Eastern Bluebirds holes should be 1 1/2” round holes, 1 3/8” x 2 1/4” vertical oval holes, or 1 1/8” horizontal slot entrances. If you are building a Western or Mountain Bluebird box, use a 1 9/16” hole. Inside the box, “kerfs” (grooves) below the entrance on the inside of the box help fledglings exit.
Floor Size — To accommodate the nest, floor dimensions are generally 4” x 4” or 5” x 5”.
Drainage and Venting — Holes should be drilled in the bottom for proper drainage and vents provided at the peak in the back.
Access — Access is one of the most important issues to address. The roof or sides should easily open to allow convenient, constant monitoring. A closure to deter mammal entry adds extra security.
When it comes to choosing a bluebird house, you’ll find several styles available. According to Sialis.com, there are more than 50 styles of bluebird nestboxes. There are pros and cons of each and debate over adaptations. Here are a few styles.
NABS Styles — These are the wooden boxes predominately seen. They provide all the basics but have a few variants.
Peterson — The Peterson box is a deeper box with an oval entrance. There is some debate that Peterson boxes with 1 3/8” oval openings are an invitation to competing starlings. Kevin Berner, NABS research chairman, reports that while starlings pass through the holes easily, they rarely nest due to size limitations. He also indicates that Eastern Bluebirds in the Minnesota area prefer Peterson Boxes over standard boxes with round holes.  This might be attributed to the deep cavity which offers better protection from the elements in a harsh climate.
|Gilbertson — The Gilbertson style is made from thin PVC plastic with a wooden roof. This style reportedly shows good house sparrow resistance as they prefer more space. It’s often painted to look like birch.||Gilwood — The Gilwood nestbox is a wooden box, designed with a u-shaped entrance hole near the roof of the house. The hinged front door opens easily for cleaning and monitoring. This box has a high field-test rating with bluebirds. It has a wide entrance hole that provides proper ventilation (more ventilation may be needed in hotter climates) and a roof that overhangs all sides. Again, it can be entered by starlings, but it’s small size is undesirable. A house sparrow trap is required with this style. ||Slot — This wooden nestbox has a large horizontal slot that is not preferred by house sparrows. However, it may be the preferred entrance by house wrens. |
No matter what style you choose to build or buy, your next steps are critical.
Location, Location, Location!
Once you choose the box, you’ll want to find a suitable location. Eastern Bluebirds prefer a wide-open habitat (no understory) with low grass. Since house wrens are competitors, place the box at least 100 feet away from brushy or wooded areas which wrens prefer. Also steer clear of places where house sparrows like to nest such as abandoned farm equipment, barns, etc.
In locating the nestbox, consider placing the box on the quiet side of the yard, away from other bird traffic, such as the feeder, particularly if you feed grain-eating birds. Make sure it is far enough from a fence that a predator, such as a cat, cannot jump.
A good site includes perching locations where parents can keep a watchful eye on the box as well as spot insects; grasshoppers, crickets, spiders, and caterpillars are their primary diet.
You’ll also want to consider where to face the box to best avoid the elements. Bluebirds are very territorial, and generally will not tolerate another bluebird box within 300 feet. Finally, if possible, place the box where you too can see it and enjoy the activity (Dave’s is only 30 feet from his house!)
Once you’ve chosen your location it’s time to put up the box. You want to put it on that tree over there, right? Or how about that fence post? Nope, neither is a good idea if you’re in an area with predators such as cats and raccoons. Instead, NABS suggests the best mount is a metal pipe (though PVC is acceptable too). Bluebird houses should be placed five feet off the ground, so you’ll need about an eight-foot pipe sunk two feet into the ground. For more details and an illustrated look at mounting your box, see the NABS instructions.
Next you’ll take steps to baffle the pole with a guard. Acceptable baffling systems include stovepipe, PVC, and metal cones. The idea here is to keep predators from climbing the pole. In addition to cats and raccoons, squirrels, chipmunks, mice and snakes can be problematic. Find instructions on baffles options at both Sialis and NABS.
No predator is more hated among avid bluebirders than the house sparrow. House sparrows, like bluebirds, are very territorial, and during nesting season can be are so aggressive in their desire for housing that they will invade nestboxes, destroy eggs and even kill bluebird babies and parents, if they trap them inside the nestbox . For this reason, deterrents are necessary. Since it has been discovered that house sparrows are uniquely afraid of shiny, moving objects, enter the “Sparrow Spooker.” This invention uses shiny mylar strips waving with the breeze to scare away the invaders. The spooker is added above the house after the first bluebird egg is laid. Many bluebirds may protest by tugging on the strips, or by staying away for a few hours, but once the first egg is laid, the bluebirds are bonded to the nestbox and will eventually adjust. Recently in the bird forum, we were treated to a chronicle of this season’s first nesting cycle by 2ndCousinDave. Here you can see how “Papa” bluebird has accepted the spooker.
Hole restrictors are used for a number of reasons, as reported by Sialis. They can protect the opening from enlargement or reduce the size of a hole for smaller species like chickadees and titmice. Wooden hole guards on the other hand are an extra block of wood used to deter a predator from reaching in the entrance hole and stealing eggs. NABS no longer recommends a wooden hole guard however.
Maintenance and Care
As responsible hosts you’ll need to be diligent monitors. Why? You’ve gone through a lot of work to create a nestbox for your bluebirds; of course you’ll want to protect them as much as possible from harm’s way. Here are some of the things you’ll check for:
- Is the house being occupied by a bird other than a bluebird?
- Is the house in good shape — no chewing by pesky squirrels, etc.?
- Is the house dry for the nest and nestlings?
- Are there wasps, bees, ants inside?
- Are blowfly larva present?
Although you might be nervous about monitoring, it is an easy and wise task. You’ll need to be checking the nest daily anyway to see when the first egg is laid (to put up the Sparrow Spooker). More information on monitoring is offered at Sialis.After the babies have fledged, 2ndCousinDave recommends cleaning and inspecting the nestbox. “I clean out my nestbox after each group fledges. If you leave the old nest in place, the BBs will build another nest on top and the eggs and babies in the new nest will be that much closer to the opening, and as such, closer to the reach of predators. The old box may contain wasp nests or other things so its good to take a close look at it each time."
Dave says that he takes his box down just hours after the last baby has fledged. This isn’t a problem for the birds, as the parents immediately take the fledglings off to teach them some survival skills. He gives the house a good scrubbing with a toothbrush and diluted solution of bleach. After it dries thoroughly, he puts the box back up because in no time at all, the female will be back to build a second or third nest.
It’s time to replace the nestbox when it appears that it has fallen into such disrepair that it is no longer a safe and healthy environment for the birds… think how much fun you’ll have shopping for or building a new one!
With a nestbox and location chosen, you’re ready to start your adventure hosting these blue angels. There’s much more to know about hosting the Eastern Bluebird though. For instance, Dave recommends making water available. He believes it is probably more important in attracting them than even mealworms, especially in the heat of the summer, not just for drinking but also for bathing. His bluebirds prefer shallow water in a sundial.
As a responsible (and now a more knowledgeable) host, you’ll be rewarded with the sweet sights of nest building, wing waving and fledgling feedings, to say nothing of their wonderful song. What a slice of heaven!
 Gilbertson Website
 NABS Website
Many thanks to those Dave's Garden members who contributed photos and information: 2dCousinDave, muddylou, f_chisolm, OPbirder, Nanegoat66 and lilyfantn.
The Bluebird Box (Audubon Society of Omaha) — Large selection of styles
NABS Plans — NABS style, Gilbertson and Peterson
Texas Bluebird Society — High heat and nestcam boxes
Northern Prairie Wildlife Research Center — One-board box and Peterson Box
More from Sialis
Eastern Bluebird Information:
“The Bluebird Monitor’s Guide to Bluebirds and Other Small Cavity Nesters” by Jack Griggs, Cynthia Berger and Keith Kridler
Bluebird-L Reference Guide, Cornell Lab of Ornithology’s Birdhouse Network and the North American Bluebird Society
Cornell Lab of Ornithology Bird Guide