Bluebird Nest Boxes – 10 Critical Features All Nest Boxes Should Have

When shopping for a bluebird nest box, you might be wondering which is the best to use. There are so many choices out there.

Some of the important features for a bluebird nest box include an entry hole of 1 1/2 – 1 9/16 inches, floor drainage, kerfs, and a roomy interior. However, there are other important considerations, especially if you’re interested in adding a nest box camera later.

This article will not only go over the basic specifications for your bluebird nest box – specs recommended by the North American Bluebird Society (NABS), but it will also take you through what seasoned bluebird trail monitors have discovered, accommodations when trying to upgrade your box and some notes about specialty nest boxes.

Something that is important to point out is that when you’re talking to several bluebirders, you’re going to get some different answers about a nest box. They may look at your choice and find a way to criticize it for various reasons. That is because, there really is no perfect nest box. But there are some that are built better than others. And the goal of this article is to direct you towards the features that make a better bluebird nest box.

Another thing about off-the-shelf/ ready-made nest boxes is that some of them are built close to right, and with a few easy modifications, you’ll be all set.

Make it easy – Get the checklist

This printable checklist will help you evaluate whether a nest box you’re interested in is up to shape for bluebirds or not. If any of the “no” check boxes are selected, rule that nest box out.

Required dimensions for bluebird nest boxes

When evaluating a bluebird nest box, the first thing you’re probably wondering about is whether it’s the right size. So we’re going to take you through what you need when it comes to size.

Here are important specifications and features to look for when selecting a nest box.

In the table below, we’ve identified sizing information that is relevant to your research when evaluating a bluebird nest box. But this table only has the minimum specifications. Certain specifications like floor size and height have other specifications that will optimize it for better health and monitoring.

Now, lets dive into each of these dimensions more, especially to understand how optimizing some of these can improve your bluebird’s experience, or your experience monitoring bluebirds.

Entry hole size

The most universal entry hole size for bluebird nest boxes is 1 9/16 inch. This will accommodate all three species. But this particular size is also going to exclude the invasive, nonnative European starling.

Being able to exclude starlings is very important because these birds regularly, fatally harm native North American birds, especially cavity nesting birds.

So, you don’t want to exceed 1 9/16 inches. You also don’t want to go any less than that if you’re housing mountain and western bluebirds. If you’re housing eastern bluebirds, you can go with 1 1/2 inches.

NOTE: A skinny starling may be able to get in. During the nesting season, birds can lose up to 20% of their body mass. However, the 1 9/16 inch hole size will do a good job excluding 80-90% of starlings poking around.

the problem with starlings, though is that this hole size will exclude their bodies. But they can still poke their heads in. So there is some potential danger to baby bluebirds.

Mandatory: For eastern bluebirds the hole size must be at least 1 1/2 inches. For mountain and western bluebirds, the hole size must be at least 1 9/16 inches. To exclude starlings, do not exceed 1 9/16 inches.

Interior drop from entry hole to floor

The drop from the bottom of the nest box entry hole to the interior surface of the floor should be at least 6 inches. Some bluebirders have suggested a maximum of 8 inches. But our personal recommendation is no more than 7.25 inches for the drop.

While that difference in height might not seem like a lot to us, to a bird like a bluebird, which is very small compared to us, a whole inch makes a huge difference. Anything too much deeper than that, and they might not like it.

Another reason to keep it just at 6 inches is because another cavity nesting bird might use your nest box. Chickadees and tree swallows are known to use bluebird nest boxes. And because these are native North American birds, we want to ensure they thrive. So keeping the drop at about 6 inches broadens the nest box so other birds can use it.

NOTE: The drop may differ on specialty nest boxes like a Gilbertson or Peterson nest box. In that case, it is alright for the drop to be shorter.

If you are using a nest lift (which we don’t recommend because bluebirds typically don’t like them), consider your drop from the bottom of the entry hole to the top of the nest lift surface.

Mandatory: Drop should be at least close to 6 inches, and not exceed 7.25 inches. We really recommend keeping it at 6 inches. A little less (like 5.5 inches would also be an acceptable compromise).

Minimum interior floor size

The North American Bluebird Society (NABS) recommends a floor size of at least 4 inches by 4 inches for eastern bluebirds and 4.5 inches by 4.5 inches for mountain and western bluebirds.

This interior floor size is a good start and will easily accommodate a bluebird family until they fledge. However, you might want to start at 4.5 x 4.5 inches whether you have an eastern, mountain or western bluebird because a larger floor size seems to encourage a full 6-egg clutch. It also allows you more room if you want to add a nest box camera.

We will bring up nest box cameras a lot in this article because they’re pretty popular. We recommend Blink Outdoor Cameras* because of how compact and affordable they are, especially when they go on sale. You can find these cameras on Amazon*, and we have a lot of other resources on our website and our YouTube channel about using and installing them.

While a 4×4 inch nest box will be able to handle a Blink Camera, the smaller size may stop a Van Ert trap from snapping all the way shut. So this is why we recommend starting with at least a 4.5 x 4.5 inch interior floor space a 4.5 x 4.25 interior floor size will also work.

Many bluebirders recommend nest boxes that are 5 x 5 inches, even 5.5 x 5.5 inches. There is nothing wrong with this size. Larger nest boxes do allow more room for growing baby birds, and they may reduce heat in a nest box because of the space available. But this size is not mandatory.

Another drawback to really larger floor interiors is that it may conflict with a Van Ert house sparrow nest box trap. House sparrows are another nonnative, invasive bird that regularly kills native birds. They too are cavity nesters, and routinely infiltrate active bluebird boxes. The Van Ert trap is a live trap that lets you catch a house sparrow and then remove it. But when the floor size (which makes the overall nest box width and length larger) is larger, a house sparrow can jump over the trap’s trigger and bypass it completely. There are ways to fix this, like taping cardboard to the trap’s trigger to enlarge the trigger. But it is something to think about.

One more downsize to anything larger than a 4.5 x 4.5 interior floor is that it may discourage smaller cavity nesting birds like chickadees from using it. They like smaller nest boxes, even 4.5 x 4.5 inches is pushing it. But they have been known to select it.

Mandatory: At least 4×4 inches for eastern bluebirds and 4.5 x4.5 for mountain and western bluebirds.

Mandatory for nest box cameras: 4.5 x 4.25 inches or larger.

Over all bluebird nest box height

There is a lot more wiggle room for the overall height of a bluebird nest box. You’ll want at least 8 inches to start with. But you can increase to 11, even 12 inches, especially if your drop from the entry hole to the floor is optimized.

We wouldn’t recommend going any higher than 12.5 inches for the interior height of the nest box because your bluebirds might not like it. And smaller birds, like chickadees, especially won’t like it.

Something to keep in mind is that while an 8 inch interior height is the minimum, this is going to be too small for you to mount a nest box camera (Blink camera) inside your nest box. So our recommendation, if you’re wanting to put a camera in your nest box is to have the interior height (that’s from the interior ceiling to the interior floor height) be 10.5 inches at its tallest end. What we mean by the tallest end is that some nest boxes are slanted or pitched to shed rain. So at the tallest part of the roof, it should be at least 10.5 inches.

Remember too that given this height, your drop should still be around 6-7.25 inches (not much more or less than that).

Mandatory: 8 inches at the very minimum. 10.5 – 12 inches is recommended.

Why bigger is better (but not too big)

While NABS has minimum requirements for nest box dimensions/sizes, we have our on recommendations based on how people are starting to use nest boxes. Other bluebirders have even encouraged larger dimensions.

Ultimately, slightly larger dimensions than what is recommended by NABS is going to allow you to add a nest box camera to your nest box, and potentially encourage a larger clutch. But you don’t want to get carried away and go too big because it may make other standard accessories harder to use, especially the Van Ert nest box sparrow traps. It may also discourage smaller native cavity birds, like chickadees from using the nest box, when they also need our help too.

Kerfs (interior ladder)

When it comes to bluebird nest boxes, kerfs are little scored or cut grooves inside the nest box just under the entry (exit, in this case) hole. They work as a little ladder to help fledglings climb up the interior wall of the nest box in order to make their first flight out.

This little ladder doesn’t have to be made from scored wood. Some nest boxes have hardware cloth just under the exit hole that serves as a ladder.

Some bluebirders say kerfs aren’t necessary. Others have experienced the horror of a fledgling that wasn’t able to get out, and the parents stopped providing care a few days after the other young fledged, and then the baby died in the nest box.

Tree swallows, who also use bluebird nest boxes especially use kerfs when fledging. Therefore, we consider this a mandatory feature for your nest box.

Many commercially available nest boxes do not have kerfs, or do not have them under the entry hole – but you can easily add them. All you have to do is carefully take a box cutter knife or utility knife or awl and score the soft wood horizontally under the entry hole before mounting the box. Go all the way to the floor, and you’ll be good to go. Or you can buy some wire hardware cloth, snip a piece to fit the interior door panel just under the exit hole, and use washers and short screws to mount it.

Mandatory: Kerfs are a mandatory feature, but if your nest box does not have it, you can easily score the wood inside to make them or install hardware cloth inside to serve as a fledging ladder.

Roof overhang

When looking for a nest box, you want some sort of overhanging roof. And just like we keep saying – bigger is better, but too big can cause some problems…

When it comes to overhanging roofs, a lot of commercially available nest boxes have the bare minimum. And that will work. Even a small overhang is better than no overhang.

At the very least, there should be about an inch of the roof hanging over the front panel of the nest box. Most commercially available nest boxes will have this.

For nest boxes with gabled roofs (which we don’t recommend), you’ll have some overhang on the sides, but you want to make sure there is overhang on the front as well.

Larger overhangs are going to keep rain and water out of your bluebird nest boxes, especially during really bad storms. And if your nest box has a lot of ventilation, that overhang becomes more important.

Overhangs that are too big, may make it hard to remove a house sparrow if you have trapped it in the nest box. This is because a lot of times, bluebird landlords will throw a mesh laundry bag over the whole nest box, close the bag, and then open the access panel. But if the roof is too large, it will be hard to fit the nest box in the laundry bag.

Some overhangs are made with grooves on the underside to direct water away from the nest box. This is not mandatory, but helpful.

Mandatory: When looking for a bluebird nest box, there should be somewhat of an overhang over the front panel of the nest box. Larger overhangs are better, but be mindful about anything too big that may make trapping house sparrows hard.

Ventilation

All bluebird nest boxes should have good ventilation. Unfortunately most nest boxes on Amazon have poor ventilation. Well-ventilated nest boxes will have vent holes on the sides of the nest box, or a vent slot on the sidse of the nest box, along with some venting on the front panel.

Ventilation is incredibly important because bluebirds nest all spring and summer long. And by July, it gets really really hot. The nest box can quickly become an oven. So ventilation that allows air to blow through the box and cool things down is critical.

Because most commercially available boxes don’t have good ventilation on the sides, you can drill holes on the sides. You want a 3/4 inch – 1 inch drill bit. Drill 3-4 holes on the upper side walls of the nest box on each side wall. Do not drill holes on the back wall. Drilling holes on both side panels will allow more air to flow through.

During the winter, it’s advised to plug up the vent holes if you have bluebirds roosting in the nest box. You can use fabric to wad into the holes to stuff them.

Mandatory: Side venting and front panel venting is a must for bluebird nest boxes. Many commercially available boxes do not have good side ventilation. But you can drill holes in the side panels for vent holes. Never drill holes on the back wall.

Access for cleaning and monitoring

All bluebird nest boxes should have a good way to access the inside for monitoring and cleaning out the nest box. Small access panels are not enough. And we also don’t recommend top-opening nest boxes because they don’t allow good monitoring, especially for blowfly inspection.

Side panels that fully pivot open or front panels that fully pivot open are ideal. Never buy a box that doesn’t have any kind of decent access for cleaning and monitoring.

Mandatory: It is a must to monitor and clean bluebird nest boxes. Pick a nest box where the side or front panel fully pivots open for access.

Floor drainage

Wood is pretty resistant to rain. But every now and then something happens, and things get damp. A wet nest box is a deadly nest box. You want water to be able to escape your bluebird’s nest box, and this is where floor drainage is very important.

When looking for a nest box, look at all of the pictures, especially of the interior or inspect it in person to see how drainage would work.

Some commercially available brands can be a bit cheap about this and have minimal drainage – mainly just being a gap between the pivoting front door and the floor of the nest box. It’s something, but it isn’t ideal.

Fortunately, an easy way to modify your nest box is to drill a small hole in each corner of the nest box’s floor. You could use a 1/4 inch or 1/2 inch drill bit.

Other nest boxes will come with the corners cut off of the floor. This creates a gap to allow moisture to exit. And this works great.

Mandatory: Drainage is a mandatory feature in a nest box. Most commercially available nest boxes lack this, but you can easily drill a hole in each corner of the floor for drainage.

4 things to avoid when bluebird nest box shopping

We’ve covered some of the mandatory features and specifications of a bluebird nest box. Now it’s time to talk about the things to avoid or things of caution when you’re shopping for a bluebird nest box.

Avoid dark colored boxes, especially dark roofs

Avoid dark nest boxes. White or natural wood color is the best. Darker nest boxes absorb more sunlight, which means more heat, and hot boxes are deadly boxes. Once a nest box gets above 103 F, your baby birds are all at risk. The eggs in the nest box are potentially at risk of becoming inviable as well.

Nature’s Way brand wooden nest boxes all have these black roofs. Avoid them, or if you were gifted one, paint it white with a water-based paint. You’ll want several layers to hide the dark color.

If you were thinking about painting your bluebird nest box, only paint it white – or a color very very close to white. Do not paint the inside. And only use water-based paints.

Avoid recycled plastic nest boxes

Bluebird nest boxes made of recycled plastic seem like a sustainable way of hosting bluebirds. We’re recycling! And they’re advertised as more durable and longer lasting than wood.

But there are several reasons to avoid these nest boxes:

1. Most bluebirds don’t like them and will choose a wooden nest box over a plastic one.
2. They heat up worse than wooden nest boxes during the summer.
3. They don’t insulate as easily during the cold winters.
4. Modifying these nest boxes to add kerfs, add a nest box camera, drain holes or extra ventilation is a lot harder.

You’re just better off using wood.

Avoid decorative birdhouses!

Decorative birdhouses are beautiful, charming and cute. But they are not suited to any native cavity nesting bird. And our native cavity nesting birds are very vulnerable right now. As hosts to these birds, we want to set them up for success not failure.

Often birdhouses leak, they’re made of thin material, and don’t provide enough access for cleaning. There are not standard sizes, so it’s hard to tell if it’s optimized to host our birds or not.

If you were gifted one, you could always use it as a decoration for inside your house, or planter for an air plant. Or plug up the hole and leave it outside as a charming, but inoperable decoration.

Always use nest boxes that are specific to the type of bird you’re wanting to attract and host.

PS. those hummingbird houses you might be seeing on social media are a scam! Hummingbirds don’t nest in houses or roost in houses. They will never use them.

Be cautious about gabled roofs – harder to work with

If built right, bluebird nest boxes with gabled roofs help shed rain, and are a more charming looking nest box. But they are harder to work with for two primary reasons:

First, it’s harder to install a wren guard on these types of nest boxes. This is an important accessory to add to your nest box after the first bluebird egg is laid in order to prevent competitive house wren invasion. But because of the shape of the gable itself, it’s just harder to add a wren guard. It takes some engineering and creativity to make a wren guard that will fit this type of nest box.

The second reason to avoid a gabled roof is that it’s harder to mount a nest box camera to the nest box. It’s not impossible. And we have a tutorial on how to do it. But it’s just more of a pain that you could spare yourself by avoiding altogether.

Another factor to consider is the seam between the two roof panels which may leak if not built right.

Where to find the perfect nest box

The perfect nest box is very hard to find. As we mentioned, a lot of commercially available nest boxes are lacking in one thing or another. But we do have some recommendations:

Nest Hollow carries the Woodlink BB3 model nest box. This is larger that most standard bluebird nest boxes and it will allow you to fit your Blink Camera without preventing a Van Ert trap from snapping. It can house all three species of bluebirds too. But it does not have kerfs. So you would need to score those yourself. The ventilation is fair, but it is better to drill holes to increase ventilation. And the drainage is bare bones. So you would want to drill holes in the bottom of the nest box. These modifications are not too hard to do, but it is a bit of a chore.

Woodlink Brand, BB3 Model Bluebird Nest Box – Roomy Starter Bluebird House

$55.99

Attract bluebirds, chickadees, tree swallows with the space they need This natural, wood bluebird nest box by Woodlink is built with larger dimensions, which makes a better space for larger clutches. This roomy nest box comes with ventilation, an extra hole guard-front opening, good drainage and is large enough to fit a nest box camera …

Woodlink Brand, BB3 Model Bluebird Nest Box – Roomy Starter Bluebird House quantity – +

Add to cart

SKU: WL24302 / WLBB3

Category: Bird House

The other best place to find a suitable nest box is to build one yourself. Nestboxbuilder.com has free plans available. And you can even download and modify those plans to fit your needs.

Notes about specialty boxes

This article is addressing the features and specifications of standard slant-roofed bluebird nest boxes. There are other types of nest boxes out there like the Gilbertson nest box, the Peterson nest box and the slot box, among others.

These types of nest boxes are what we like to call specialty nest boxes because they were designed to fulfill a specific role.

For instance, Gilbertson nest boxes are made to discourage house sparrows. They are sometimes marketed as house sparrow-proof or house sparrow-resistant but no nest box is 100% house sparrow proof.

Peterson nest boxes were designed to make it harder, but not impossible for predators to access. The Peterson box is a good choice for experienced bluebirders who manage a trail and pair this nest box with a proper baffle.

We have a whole article that goes into more detail about the purpose of these different specialty nest boxes and the pros and cons of each one.

For beginning bluebirders, and backyard bluebirders, we recommend just sticking with a standard nest box.

Educational Bluebird Coloring Book

Learn all about hosting bluebirds, from what kind of nest boxes to use, how different specialty nest boxes work, how to protect from predators and competitors, and so much more. As you color, you’ll learn all about a given topic. This coloring book is available on Amazon*, and your local bookstore can order it as well.

*These links use affiliate links. As an Amazon Associate, Nest Hollow earns from qualifying purchases. This does not cost you anything extra, and the amount earned helps pay for the expense of this website and YouTube channel.