To those who build and/or install or promote barn owl nest boxes,
This is a request to come together and agree on minimum overall size requirements and entry hole dimensions and placement.
We see a vast range in dimensions (below). We believe the smaller boxes are an attempt to keep the boxes lightweight, less expensive and easier to install, but that’s not fair to the owls. That’s like saying that you need to live in an 8’ X 8’ home because that’s easiest and less costly.
34.5 X 21 X 23
30 X 14 X 16
26 X 17 X 17
23 X 11 X 16
23 X 12 X 16
23 X 16 X 12
23 X 12 X 16
23 X 16 X 12
18 X 10 X 22
17 X 15 X 22
12 X 12 X 16
Barn owls stand about 14” tall with a wingspan as great as 43”. We have watched a male roost in the same box with his mate while she’s brooding. Even with six chicks, we have seen both parents stay in the box during the day until they were about a month old. We credit this to the size of our boxes, allowing enough room for the family to stay together. As owlets near fledging age, they need to exercise their flight muscles. We’ve watched them hop and pounce and flap their wings - practicing being an owl. There’s no room for owlets to do that in a small box.
We agree with the Barn Owl Trust’s minimum floor size for an American barn of about 29” X 23.6” (50% greater than for the European species).
An ideal nesting box would be much bigger: a full 1 metre (39.37”) from the bottom of the entrance hole to the bottom of the box and with a floor area of at least 1 metre (39.37”) x 1 metre (39.37”). However, owl boxes that big would be very difficult to erect and more expensive. (Barn Owl Trust web site)
ENTRY HOLE PLACEMENT AND SIZE
From bottom of entrance hole to nest floor must be not less than 18”. (Barn Owl Trust web site)
Again, we agree with the Barn Owl Trust, that the nests should be deep. Placement of the portal is critical for the welfare of the young owls. Too low, and the young owls will fall out prematurely, risking injury and death.
We have found that 10” - 11” from the base of the floor (with 2” shavings) to the entry hole can keep young owls contained until they are light and mostly flighted, but if the height of your box allows for it, place the entry at the suggested 18”.
The size of the hole is also critical. Too large, and predators will have easier access. But the hole can be too small. From research and experience, we believe the entry hole should be elliptical 5 1/2” wide by 4.5” high or a 5” square.
TAKE THE PLEDGE
Providing barn owl nest boxes is about providing a safe location for a pair of owls to raise their young - that has to be our priority. We mustn't let convenience be an excuse for substandard nest boxes.
Please, pledge with me now to only build/install adequate nest boxes with minimum width of 16” and a length that achieves a diagonal measurement of 36” and a height no less than 18”. Pledge to make entry holes no less than 10” above the surface of the floor, accounting for shavings and buildup of pellets.