Who doesn’t love the sight of bluebirds? There is something oddly reassuring about their cheery presence, a feeling that all’s right with the world (although that’s clearly an illusion these days). When bluebirds start house-hunting in earnest in late winter, usually late February, Spring is never far behind. That thought alone is uplifting.
Bluebirds, members of the thrush family, were once common in Pennsylvania orchards and homesteads. Their numbers suffered a steep decline when English sparrows and starlings begn pushing them out in the last century, along with DDT use in the 1950’s. Fortunately their numbers have been increasing slowly but steadily in recent years. They are now making a modest comeback in semi-rural and suburban areas, thanks to numerous efforts by nonprofits, homeowners and community nest box programs.
If your property has an open patch of yard free of disruptive elements, there are a few things you can do to try and lure them in.
If you live in town or close to heavy traffic, getting bluebirds to visit will be difficult to impossible. If on the other hand, scattered woodlots and weedy margins dot your neighborhood, with abundant grass and maybe a stream, it’s quite possible. Nearby parks, vacant grassy lots and even golf courses are ideal. Bluebirds do not mind human activity as long as no one bothers them. They can suffer from cat predation though, as do all songbirds, so do whatever you can to minimize any feline challenges. If you have outdoor cats they may pass you by.
Increase your insect population
Having a ready supply of insects on which bluebirds can feast and feed growing chicks is critical. But you don’t need to be a one-person nature preserve. Adding native plantings to your existing landscaping and not using pesticides will go a long way toward increasing your insect population (including beneficial insects in the garden). Berries and fruit-bearing shrubs also help immeasurably, especially in winter. For more on these topics, see these related articles:
Put up a bluebird box
Bluebirds are cavity nesters, meaning that in the wild, they use old woodpecker holes or any dry, sturdy cavity that’s safe and warm enough to raise chicks. Fortunately they readily accept manmade nest boxes — provided they’re the right size, face the correct direction, and provide a clear flight path within an open grassy area.
These are not trivial points; bluebirds are very particular about their nest boxes for good reason. Like all birds, they have natural enemies; bluebirds will instinctively avoid features that enhance risk of predation or chick death.
Build or Purchase?
There are numerous bluebird box styles on the market. Be sure whichever one you buy meets minimum bluebird specifications. Audubon-branded houses are excellent, as are those made by Nature’s Way (certified by the North American Bluebird Society). Wild Wings also makes a good design. You want to maximize chances of bluebirds nesting there, not encourage sparrows and wrens.
I strongly recommend wood or plywood over composites. The latter get too hot in direct sun. Cedar and cypress make excellent bird houses because they last many years and resist rot. Avoid pressure treated lumber (for the box) because it contains poisonous chemicals like arsenic. But you can use pressure-treated wood for the post.
There are kits you can buy, or build your own from plans available online. Just make sure the box can be opened for cleaning, has air vents and drainage holes, and the entrance hole is the proper size. More on this below.
Should you paint it?
I happen to think unpainted boxes are more readily accepted, as they most closely mimic a bluebird’s natural habitat. If you do paint your box, use a light shade of gray or beige that reflects heat; white or bright colors are too off-putting. Remember, birds have excellent color vision. Songbirds especially want to hide their nests, not advertise them to marauding wrens and sparrows.
Entrance hole
The entrance hole must be 1 1/2″ in diameter for Eastern bluebirds, or 1 9/16″ for Western bluebirds. Most boxes sold nationally have 1 9/16″ holes for this reason. Any larger, and jays, starlings and cowbirds will either destroy or exploit the nest relentlessly.
Please avoid perches. A perch is a liability for bluebirds; they just invite other birds to sit at the entrance and harass the chicks. Bluebirds will easily cling to the box itself and hop in and out just fine. They prefer boxes without a perch because they are safer.
Most boxes now come with a predator guard— nothing more than an additional thickness of wood or a plastic tube surrounding the entrance hole. This makes it much more challenging for a racoon to angle its paw into the box to grab eggs or chicks. I don’t have a guard on mine but I may add one soon, as racoons often pass through and could reach in to get at the chicks (and yes, racoons readily eat baby birds). Bluebirds seem to have no problem navigating a guard.
Unfortunately, guards don’t stop house wrens or English sparrows. These interlopers regularly get into 1 1/2″ holes with disastrous results. Wrens in particular are very aggressive and will throw out and chase nesting bluebirds and destroy any eggs, taking over the box for themselves. They are the single biggest menace bluebirds face. Keep an eye out and promptly evict them! This may mean opening the box.
Are there eggs?
Bluebird eggs are plain blue, usually a little larger and deeper blue than a robin’s. Heavily speckled pale blue or small reddish-brown eggs belong to wrens or house sparrows. Obviously the presence of other eggs means the bluebirds were evicted. Once a wren or sparrow has taken over a bluebird nest and laid her own eggs, it’s too late for the bluebirds for this clutch– they’ve already moved on.
If there aren’t any foreign eggs yet and the bluebirds are hovering nearby, remove whatever new nest material the sparrows or wrens have added. Close the box and hope for the best. If there are both bluebird eggs and foreign eggs present, it’s up to you to decide if you want to remove the interloper eggs or let nature take its course. (If you do remove them, the wrens might simply lay more.)
Prevention is easiest
The best strategy to prevent this distressing scenario is to put up a wren or sparrow box at the opposite end of your property. Do this no later than April 1st. Locate it at least 50 yards away from the bluebird box; 100 yards is even better, so their territories don’t overlap.
If given a choice, wrens and sparrows will use an unoccupied box before taking over an occupied one. Since a wren box has a smaller hole, no other species will use it; but sparrows will nest in anything they can squeeze into. Both wrens and sparrows are oblivous to bright colors, wacky dimensions and construction materials, so fanciful designs are fine. Do make sure you can clean them easily.
Lastly, bluebird boxes that are close to woods attract wrens and sparrows more than those in an open setting. I have no choice because my yard is so small. But I do erect a wren house out front, and my neighbor puts up numerous houses, so that helps a lot.
Dimensions and Air Flow
Boxes measuring 5.5″ to 6.5″ in interior width and depth and 12″ high are the right size. But many on the market are too small or too narrow, with not enough room for the mother to sit comfortably. Ample height is needed to accommodate the nest, chicks and mother bird and still have air adequate space above. Don’t skimp on this.
Critical top vents and bottom drain holes regulate the box’s temperature and discourage chick mortality from mold, mites, and dampness. Be sure yours has these features (and if not, drill a few holes to create them). One design even has a mesh platform an inch above the floor, helping to prevent ant and mite infestation and improving air circulation too. This is not necessary but it will help.
Mounting and Orientation
The box should be mounted on a sturdy pole with pipe brackets or a 4X4 post, between 4 and 6 feet off the ground for ease of maintenance (fencepost height). If other wildlife are present, adding a predator or squirrel baffle on the pole is a good idea; homemade is fine. Otherwise, snakes can crawl up the post to get at the eggs — I once witnessed this. Mice absolutely love bird houses and will often move in after the chicks fledge, preventing further use until you kick them out. Don’t mount your house on a tree trunk, either.
Ideally, face the box south or southeast in plenty of sun; due east is second-best. This orientation warms the box quickly on cold spring mornings and the birds prefer it. Designs with a front roof overhang and a downward tilt shade the hole from direct sun, preventing the chicks from broiling to death. If possible, try to locate the house where there it will be a little dappled to full shade on hot afternoons.
Bluebirds will not use a box in full shade or in woods, but they will readily tolerate woodland edges. But the closer to woods, the more likely wrens will be a problem, so it’s a trade-off.
Not optional: Bluebirds must have a meadow, wide lawn or mown fields close by in which to catch flying insects, ideally located directly in front of or surrounding the box.
Provide the Right Cover
Low shrubs, a fenceline or trees nearby is ideal. The male is always first on the scene each spring. He scouts for suitable nesting sites and shows them to the female when she arrives. Once she picks the box she wants, he will find a good lookout perch with a direct sight-line to the box while the female is inside, patroling for rivals and evictors. Good cover nearby but not too close will make your box’s location more appealing, therefore more likely to get chosen.
More is not Better
Finally, please don’t erect multiple boxes near each other unless they’re at least 100 yards apart. Yes, that far! Bluebirds are fiercely territorial and will not allow other bluebirds to nest within a 100-yard circumference of their nest, regardless of whether there are other boxes present or not. The unused boxes will just attract wrens and sparrows and create a lot more patrol work for the male.
So no worries if your yard can only hold one box; one is quite enough!
A fresh source of water is always a good idea, but not necessary if you can’t manage it. All birds including bluebirds appreciate a clean water source. They also like bathing.
In fall or late summer after the last chick has fledged, clean out the box thoroughly and make any repairs. It needs to be clean and empty in February, when next year’s birds will be inspecting it for suitability. They won’t use a box containing an old nest, bird waste, ants, or paper wasps on the interior ceiling. It’s much easier to clean it now than to wait, when you may forget.
Don’t neglect winter forage
Since bluebirds are primarily insect and berry eaters, in winter they enjoy soaked (softened) raisins and dried mealworms. They rarely come to seed feeders but they will definitely come for mealworms, especially when there’s little else to eat. They will also eat hulled sunflower seeds, suet, peanuts, and any berries still hanging on in the landscape.
Sometimes you will get a flock of winter bluebirds passing through, making an appearance at your feeders for only a few minutes. Or come spring, they’re around, but ignore the box you put up. Don’t despair, that happens sometimes.
Putting out food for them in winter greatly increases the chances any migrants will stick around long enough to find your box, and a few may even roost in it on bitter cold nights. If they do, it’s highly likely one pair will stay behind and raise a brood.
All of these steps when taken together add up to an amenable habitat for these lovely birds. If you don’t succeed at first, keep trying. It took two years at my former property to attract bluebirds initially; from then on, residency was intermittent but regular over a span of 25 years.
At my current property, it took four years before we had our first nesting pair, who raised two broods that year. I had high hopes for 2022 since the pair in the photo above started scouting our box in January! But the wrens evicted them, sadly. Let’s see what happens this year.
Good luck!
