Owl Box Guide: Sizes and Placement for Barn and Screech Owls

Match the box to the owl you actually have. In the US, a screech-owl box has a 3-inch (76 mm) hole and goes 10 to 30 feet up at a wooded edge; a Barn Owl box is several times bigger and belongs beside open fields, 8 to 25 feet up. In the UK, the realistic targets are the tawny owl in mature woodland and the Barn Owl on farmland. Hang any of them in autumn or early winter.

Which owls use nest boxes

Only cavity-nesting owls use enclosed boxes: in North America, screech-owls, Barn Owls, Northern Saw-whet Owls and Barred Owls (not Great Horned Owls); in Britain, tawny owls and Barn Owls.

For most US backyards the realistic tenant is a screech-owl, which All About Birds says lives almost anywhere with enough trees, from farmland to city parks. Barn Owls are farm and marsh birds; Barred Owls want mature forest near water.

Before you buy, listen outside on a still night in late winter. Eastern Screech-Owls give a descending whinny and a long even trill, tawny owls the familiar hoot and “ke-wick”, and Barn Owls a harsh drawn-out scream. Merlin Sound ID will confirm it. If owls already call nearby, a box has a real chance.

Owl box sizes by species

Figures are from Cornell Lab’s NestWatch for US species and the Barn Owl Trust and RSPB for the UK. Floor and depth are inside measurements.

The entrance decides who gets in, and depth below the hole keeps owlets inside and eggs beyond a raccoon’s reach. That is why the Barn Owl Trust sets a 450 mm minimum and calls deeper “much safer”. The Trust also says North American Barn Owls are bigger and need about 30 percent more depth and floor area than UK birds, with the entrance kept the same size. For songbird holes, see the birdhouse hole size chart.

Where to put a screech-owl or saw-whet box

NestWatch’s advice is specific: mount the box under a limb at the edge of woodland near fields or wetlands, on a tree at least as wide as the box, 10 to 30 feet up. The entrance can face any direction. A branch nearby helps young climb out, as long as it does not block the hole. Space boxes at least 100 feet apart, and add 2 to 3 inches of wood shavings, because owls bring no nest material.

The tree-or-pole question comes down to squirrels. The Tennessee Wildlife Resources Agency prefers a pole with a predator guard, far enough from trees that squirrels cannot jump across, and says to avoid sites with heavy insecticide or herbicide use. Maryland DNR accepts a live tree or a pole near a woodland edge and water, away from roads and paths.

Saw-whets are pickier: 12 to 15 feet on a live tree in conifer forest near water, boxes about 800 feet apart.

Where to put a Barn Owl box

Open land first, box second. Barn Owls hunt low over rough grass, so a box inside a wood is wasted. In the US, NestWatch lists 8 to 25 feet up on a pole, barn, silo or large tree beside fields, 100 feet between boxes. It also warns that hungry owlets are loud at night, so do not mount one right outside a bedroom window.

The Barn Owl Trust adds rules worth following on either side of the Atlantic:

• Indoor boxes in barns and outbuildings that overlook open ground last longest and are preferred.
• On a tree, choose a mature, thick-trunked tree that stands alone or on a hedgerow or woodland edge, with few low branches, so a passing owl can see the hole even in full leaf.
• Face the hole towards open ground and away from the prevailing weather.
• Ideally be within 1 km of rough grassland, and avoid sites within 1 km of a motorway, dual carriageway or fast unscreened road, where young owls are killed.

Where to put a tawny owl box

Tawny owls are woodland birds and will use a box in a large, well-wooded garden. The Barn Owl Trust suggests one of the most mature trees, preferably inside the wood rather than on its edge, at least 3 m up in quiet sites and 3.7 m or more where people walk past. The classic chimney design is strapped under a side branch at about 45 degrees.

Face the entrance away from the prevailing wind. The RSPB says east, north-east or south-east, and both the Trust and the BTO say to avoid west and south-west. The RSPB says no nest material is needed; the BTO plan suggests about an inch of large wood chippings so eggs do not roll. Keep the flight path clear and leave branches near the hole so owlets can climb into the canopy.

When to put up an owl box

Autumn and early winter, because owls choose sites weeks before laying. Maryland DNR says Eastern Screech-Owls set up territories in mid-February and begin nesting in early March, and advises hanging boxes by mid-January. Tawny owls breed earlier still: the Barn Owl Trust gives mid-March as the usual first-egg date, and the RSPB notes laying from February or March. Barn Owls in mild US climates can nest in almost any month. For other species, see when to put up birdhouses.

Keeping starlings, squirrels and raccoons out

• Starlings stuff owl boxes with grass in early spring. In the US they are invasive and not protected by federal law, so you may remove their nests. Check in late winter.
• Squirrels fill boxes with leaves. A smooth metal band about 2 feet tall around the trunk, or a baffle on a pole, stops them climbing. Keep the box away from branches they can jump from.
• Raccoons and cats reach into shallow or low boxes; keep boxes deep and above 10 feet. See keeping cats away from birds.
• Kestrels, Wood Ducks and jackdaws are native and protected. Leave them and put up another box.

Two habits raise the odds more than any box feature: stop using rodent poison where owls hunt, as NestWatch advises, and keep outdoor lights off the box and its approach. NestWatch also suggests a second screech-owl box in the same territory, since a pair rarely renests in the same site.

Cleaning and checking

Clean once a year when the box is empty. NestWatch suggests December for Barn Owl boxes; the Barn Owl Trust clears UK boxes between November and January in dry, calm weather, and only every two or three years when only Barn Owls use them. Tawny boxes are best checked in early autumn.

Screech-owls roost in boxes all winter, so look before you open one. Wear gloves and a dust mask, scrape out old pellets and starling nests, then add fresh shavings: 2 to 3 inches for screech-owls, or a thin 3/4-inch layer for Barn Owls, which build their own base from shredded pellets.

Never open a box during laying and early incubation. NestWatch warns females may abandon, and in the UK the Barn Owl Trust is clear that disturbing breeding Barn Owls is illegal. The general method is in when and how to clean out a birdhouse.

Buy or build

A screech-owl box is an easy first build: 3/4-inch untreated cedar or pine, a 3-inch hole saw and the NestWatch plan. Leave the inside raw, cut grooves below the hole, drill drainage in the floor and fit a side or front door. For any box, safe mounting at height with a pole, guard, ladder and a second person is usually the harder part.

If you buy, look for the right entrance, plenty of depth below the hole, drainage and vents, a door that opens, a grippy inside wall and no perch.

The three boxes worth buying

This guide is research-led. We have not installed or monitored these boxes; the specs below are the makers’ own published figures.

JCs Wildlife Cedar Screech Owl Nest Box. Cedar walls, a recycled poly roof that will not rot and a latched flip-open front for quick ladder clean-outs. The 4 x 3-inch oval entrance sits 9.75 inches above the floor, and shavings are included. The walls are 5/8 inch, thinner than most plans, and the box is shallower overall than the NestWatch design.

See available listings on Amazon

Coveside Saw-Whet and Screech Owl House. The closest match to the plan-style box: Eastern white pine, a 3-inch round hole, 11 x 9 x 17.75 inches outside, vent slots, drainage and a lift-up side panel. Pine weathers, so check it every few years, and fit a guard if squirrels are around.

See available listings on Amazon

JCs Wildlife Barn Owl Nesting Box. Exterior plywood, 24 x 21 x 19.25 inches, with a 5.5 x 4.5-inch oval entrance and an internal divider that keeps the nest out of reach of a raccoon or Great Horned Owl at the hole. The end door also takes a wildlife camera. It needs a strong mount and two people; a recycled poly version and a DIY kit come in the same size.

See available listings on Amazon

If an owl box is not a fit

A box will not create hunting habitat. On a small lot with few trees, leave safe dead trees standing, let a corner grow rough and put up a songbird box from the best birdhouses roundup instead. For mounting hardware on any box, see how to mount a birdhouse on a pole, tree or wall.

Sources

• Eastern Screech-Owl nest box, NestWatch, Cornell Lab of Ornithology
• Western Screech-Owl nest box, NestWatch
• Northern Saw-whet Owl nest box, NestWatch
• Barred Owl nest box, NestWatch
• Barn Owl nest box, NestWatch
• Eastern Screech-Owl life history, All About Birds
• Barn Owl nestboxes for buildings, Barn Owl Trust
• Barn Owl boxes for trees, Barn Owl Trust
• American Barn Owls, Barn Owl Trust
• Tawny owl nestbox, Barn Owl Trust
• Tawny owl nest box instructions, RSPB
• Tawny owl nest box plan, BTO
• Eastern Screech Owl nest box, Tennessee Wildlife Resources Agency
• Habitat Project: Eastern Screech-owl boxes, Maryland DNR