When and where to put up a nest box

A nest box is the rare piece of backyard equipment that can do real harm if you get it wrong. A feeder placed badly means fewer birds. A box placed badly means a raccoon eats a brood that would otherwise have fledged — you have concentrated eggs into a predictable container and advertised its location.

Done right, though, boxes work. Bluebird populations recovered across much of North America substantially because ordinary people put up boxes and maintained them. Here's what "right" means.

Timing: earlier than you think

The goal is to have the box up four to six weeks before the first eggs, so birds prospecting for territory find it during the search rather than after.

For most songbirds that means late winter: February in the South, March through the mid-latitudes, early April in the far North and at elevation. In practice, if you can put a box up any time from December through February you are comfortably in front of the season.

Two useful exceptions. Woodpeckers and owls want boxes in fall or winter — they roost in cavities through the cold months and often claim a box long before nesting. A screech-owl box put up in October may hold an owl by November. And a late box is not a wasted box: many species raise second and third broods, so one mounted in June still gets used, and either way it's ready next February.

Purple Martins run on their own schedule. Their housing stays closed until scouts are expected locally — February on the Gulf Coast, April in the northern states — because opening early hands the compartments to House Sparrows and starlings.

Habitat first, everything else second

The single most common failure is a box in perfectly good condition, mounted at exactly the right height, in habitat the target species does not use.

Bluebirds want open ground with short grass and scattered perches — pasture edge, orchard, big mown yard, cemetery, golf course rough. A bluebird box in the middle of woods will get chickadees or wrens instead, which is fine, but it will not get bluebirds.

Chickadees, titmice, and nuthatches want the opposite: woodland edge or a wooded yard with cover close by. Tree Swallows want open ground near water. Wood Ducks want wooded swamp or a beaver pond, with the box over water or within about 100 feet of shore. Kestrels want open farmland or grassland with hunting perches and a clear approach.

Look honestly at your ground and pick the species that matches it, rather than picking the species you want and hoping.

Height, orientation, and spacing

Mounting heights vary by species — 4 to 6 feet for Eastern Bluebird, 6 to 10 for House Wren, 10 to 20 for woodpeckers and screech-owls, 10 to 30 for kestrels. Within those ranges, the exact number matters much less than people assume. Convenient monitoring height is a legitimate tiebreaker: a box you can open weekly is a box you'll actually manage.

Face the entrance away from prevailing wind and driving rain. Through most of North America that lands you facing east or northeast, which has the side benefit of catching morning sun and avoiding the worst afternoon heat. In hot southern climates, avoiding a west-facing entrance matters more than anything else about orientation.

If you can, aim the entrance toward a shrub, fence, or tree 25 to 100 feet away. Fledglings leave the box on a first flight that is more of a controlled fall, and a landing target within gliding distance materially improves the odds.

Spacing depends on how territorial the species is. Eastern Bluebirds want at least 100 yards between boxes, and 125 to 150 is better; Mountain Bluebirds want 200 to 300. Chickadees hold smaller territories, roughly 100 feet. Wood Duck boxes should be out of sight of each other entirely — visible neighbors cause dump nesting, where several hens pile eggs into one box and none of them hatch.

The exception worth knowing is pairing. Where Tree Swallows compete with bluebirds for every box, mount two boxes 5 to 20 feet apart and space the pairs normally. A swallow pair defends its territory against other swallows but tolerates bluebirds next door, so you get one of each instead of two swallows.

The predator guard is the whole game

If you take one thing from this: a box without a predator baffle is a box that feeds raccoons. Not every year, not every box — but over a few seasons on an unguarded box, something finds it.

The setup that works is a smooth metal pole with a stovepipe or conical baffle mounted below the box. Not a wooden post, which is a ladder. Not a fence line, which is a highway. Not a tree trunk, which cannot be effectively baffled at all — this is the main argument for pole-mounting instead of tree-mounting whenever you have the choice.

Add a hole guard — a wooden block or metal plate that extends the entrance tunnel — where squirrels are a problem, since they will chew a hole wider until it admits them, and starlings follow. And place boxes away from feeders, brush piles, and anything else that concentrates cats and raccoons.

Which brings up the perch. Never mount a box with a perch below the entrance. Cavity nesters cling to the hole; they have never needed one. What a perch provides is a seat for a House Sparrow harassing the occupants and a brace for a raccoon reaching in. Boxes are sold with perches because perches look right to buyers, not because any bird asked for one. If yours has one, saw it off before you mount it.

Monitoring, and the sparrow problem

Check the box weekly during the season. Tap the side first, open it, look, close it. Careful monitoring does not cause abandonment — most songbirds tolerate it well — and it lets you catch problems while they're fixable: wasp nests, blowfly infestation, a failed brood, or a House Sparrow takeover.

That last one requires a decision. House Sparrows and European Starlings are nonnative and not protected in the US, and they kill native cavity nesters — a male House Sparrow will peck an adult bluebird to death inside her own box. Their nests may legally be removed. If you are not prepared to manage them, a box in sparrow-heavy habitat may do more harm than good; that's a real fork in the road, not a technicality.

Every native species is protected, including the House Wren that stuffed your bluebird box with sticks. Once eggs are present, leave it alone and adjust your placement next season — wren boxes belong near cover, well away from bluebird boxes.

Clean out the old nest after each brood fledges. It encourages a second attempt and cuts parasite loads. Do a final clean before the season starts, and check that the drainage holes are clear.

A short pre-flight check

• Untreated wood, ¾ inch thick or more. No interior paint or stain.
• Rough or grooved interior below the hole so nestlings can climb out.
• Drain holes in the floor, ventilation near the top.
• Opens from the side or front for monitoring.
• Correct hole diameter for the target species — check the spec finder, since a sixteenth of an inch decides whether starlings can enter.
• No perch.
• Baffle on a smooth pole.

Get those seven right and the birds will handle the rest.