3/4" CDX. The base dimensions I use are 12x12". The front is 12x16. Back is 12x20. Sides, of course are angled 12x16 to 12x20. Top is 20x20" to overhang a couple inches on the sides and front. Hole centered 5" down from the top is oblong 2 1/2 x 4" (long axis horizontal). This way, two full boxes can be made from a sheet of plywood. If you make them from cedar or redwood dimensional lumber, they will last a lot longer, but, of course, much more expensive. Don't use OSB as it starts to flake and fall apart in about 2 years. Don't paint them. Work good for boreals, saw-whets, screech owls. Need to be at least 20' off the ground. Best if there is no brush immediately below the box.

The last image i put in (above) is an adult female boreal owl just returned to the nest box. They drop their wings like that, then quickly squeeze into the box, turn around, and peek out watching.

Very important, especially in colder climates, to provide 4-5" of nesting material in the bottom of the box (I use planer shavings) or the eggs will freeze in early spring.

Not mentioned above, but kestrels really take to the boxes as well if the earlier-nesting owls aren't using them.

Jack

Jack

Thank you for the replies and some great pictures.

Thanks.I might have to build some of those.

I am sure this wont be popular, but why would anyone want more owls around?

Less wild house cats running around killing everything.

A friend has a wood duck box that has never been used by woodies, but the screech owls are there about every year.

trapNH -

The smaller owls that are cavity nesters are generally mouse/vole specialists. The more of them I have around my place, the more feed there is for domestics (cows/horses) and for deer/elk. Too, the larger platform-nesting owls do tend to keep the house cat numbers down a bit.

I've found that leaving 1 side of the box open will keep the squirrels from taking over. A short lip on that side will keep the wood chip/saw dust nesting material in, and I put that on the north side to keep direct sun out.

Do the smaller owls help control mice/voles?

Jack

That’s a awesome picture.

I like the pic the to me the owl has the oh crap you caught me look, thats the main reason I want to use them is the mice and voles, but do hope they take the gophers they can get also.

Love that pict. Too!

Absolutely gorgeous, Jack. The lighting, shade above accenting the head , perfect.

Do you find the need to clean your boxes every year?

Tray -

Yes. Seems to be important to clean out the boxes and put in fresh wood chips if the box was used.

Do the Great Horned Owls Utilize nesting boxes? Have to be pretty big box.

So will that owl actually utilize all of that prey herself or is she "putting food by" for when her eggs hatch ?

OR.......is it just habit for her to keep hunting whenever the opportunity presents ?

No. Great horned owls are platform nesters rather than cavity nesters. Like most owls, they don't construct their own nests, but usually take over red-tailed hawk (or similar hawk, eagle) nests. They are early nesters (usually start nesting in February/March in this country), so they can take over a nest long before the hawks start their nesting. If you want to encourage GHOs to nest, there are plans on the internet for building platforms that the GHOs or the Great Grays will use.