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Sparrow Birdhouse Hole Size: 1 1/4 Inch, and the Catch

Native sparrows use a 1 1/4-inch entrance. House sparrows are invasive and no hole size excludes them reliably — what to do instead.

By Salma 2 min read Save to Pinterest — opens Pinterest in a new tab
A blue tit perched on the peg of a bare timber nest box beside its entrance hole
Photo: 11066063, Pixabay Content License, via Pixabay
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The number itself is simple — 1 1/4 inches — but the question usually hides a different one: how to keep house sparrows out. That part has no answer in hole size.

Entrance hole sizes by species

specieshole
Chickadee, wren, titmouse, native sparrows1 1/4 in
House sparrow (UK, as provision)1 1/4 in
Nuthatch1 1/4–1 3/8 in
Eastern bluebird1 1/2 in
Western / mountain bluebird1 9/16 in
Tree swallow1 3/8–1 1/2 in
Purple martin2 1/8 in
Flicker, screech owl3 in

North America and the UK want opposite things

In North America the house sparrow is introduced and displaces native cavity nesters, so boxes are designed to discourage it. In Britain it is a declining native on the Red List, and a multi-chamber sparrow terrace under the eaves is a genuine conservation measure.

What actually discourages house sparrows

  • Slot entrance, 1 1/8 inches tall. Bluebirds and chickadees take to it; sparrows use it less
  • Siting. They want buildings, paving and feeders nearby. Put boxes out in open ground, 100 ft or more from the house, and away from the seed feeder
  • Monitoring. Checking boxes weekly in the breeding season and clearing sparrow nest material early is the only thing that reliably works where they are already established
  • No perch, and a box that opens so you can see what is inside

The rest of the box matters more than the hole

  • 3/4-inch stock minimum, with a hole guard plate over the entrance
  • Drainage holes in the floor and vents under the roof
  • Rough or scored interior below the hole so young can climb out
  • Pole-mounted with a baffle, not nailed to a tree
  • Cleaned out annually, after the last brood fledges

Common questions

What hole size should a sparrow birdhouse have?

For native North American sparrows and small cavity nesters, 1 1/4 inches is the standard diameter — the same size used for chickadees, wrens and titmice. For the European house sparrow, which is what most people actually mean, a 1 1/8-inch hole limits them somewhat but does not exclude them, and they can use anything from about 1 1/8 inches upward. In the UK, where the house sparrow is a declining native, a 1 1/4-inch hole in a box with a sparrow terrace design is the right provision.

Can you keep house sparrows out of a birdhouse with a smaller hole?

Not reliably. House sparrows will use a 1 1/8-inch hole, which is the same size that chickadees need, so there is no diameter that admits small natives and excludes sparrows. What works better is a slot entrance about 1 1/8 inches high, which bluebirds and chickadees accept and sparrows use less readily, plus siting boxes away from buildings, feeders and paving — house sparrows strongly prefer nesting near human structures.

What is the hole size for a bluebird house?

1 1/2 inches round for eastern bluebirds, 1 9/16 inches for western and mountain bluebirds, or a 1 1/8-inch tall slot entrance. The size matters in both directions: too small and the bird cannot enter, too large and starlings get in. A 1 1/2-inch hole keeps European starlings out, which is one of the main reasons the dimension is so specific.

Does hole size keep predators out?

It helps, but thickness and hardware do more. A correctly sized hole in 3/4-inch stock resists enlargement, and a hole guard — a second plate of wood or metal over the entrance — stops squirrels and woodpeckers chewing it wider. The bigger predator risks are climbing: a pole-mounted box with a baffle is far safer than any box nailed to a tree, whatever the hole size.

Should a birdhouse have a perch below the hole?

No. Cavity nesters do not need one — they grip the entrance and the wall directly — and a perch gives house sparrows, starlings and predators somewhere to stand while harassing the nest. Commercial decorative birdhouses almost always have one, and removing it is the first upgrade to make. Roughen or score the inside wall below the entrance instead, so fledglings can climb out.

In the UK, should I be excluding house sparrows?

No — the opposite. The house sparrow is a native species in Britain and has declined steeply, and it is on the Red List of conservation concern. Putting up a sparrow terrace, a box with two or three chambers and 1 1/4-inch holes mounted high under the eaves, is positively useful there. The advice to exclude house sparrows applies in North America, where the species is introduced and displaces native cavity nesters.

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