Poor Barn Owl nestbox design

Every year, nestling Barn Owls fall from poorly designed nestboxes and die.

Poor nestbox designs cause a variety of problems. They include any type of nestbox that:

What is a ‘flat’ or ‘shallow’ design nestbox and what’s wrong with it?

We call a ‘flat’ nestbox any that has the access hole at or near the same level as the nestbox floor. A ‘shallow’ nestbox may have a depth of as much as 250mm but this is nowhere near enough and the owlets will still get out easily. Premature emergence increases the chances that they will fall from the box. When finding a nestling bird, the advice for almost every other species is to leave well alone as the adults know where it is and are feeding it. However, this is absolutely the wrong advice for Barn Owls. A fallen owlet will either starve slowly or be predated unless replaced in the nestbox. Here’s what to do if you find a fallen owlet.

What’s the solution?

In order to reduce the risk, all Barn Owl nestboxes should have the access hole at least 455mm above the bird’s nest. This keeps the owlets safe from falling until such time as they start to fledge. The lift they get from their developing flight feathers then allows them to exit the nestbox at the appropriate time. Good nestbox designs also facilitate the re-entry of young birds that may have exited the box but are not quite ready to fly. Positioning boxes within easy reach of perching places (such as a roof truss or tree branch) also makes them safer for emerging young. Pole-mounted boxes (that, by definition, lack nearby perches) are 540mm deep so the young cannot possibly emerge until they are capable of flying upwards.

Poor Nestbox Design Indoor Flat Box     Good Nestbox Design Indoor Deep Box

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Why is it important that the contents of the nestbox stay dry?

Barn Owls don’t use any conventional nesting material. Rather, the female lays her eggs on a layer of compacted pellets to form what is called a nest debris. This nest debris is a highly absorbent layer of small mammal fur that soaks up the faeces that the owlets squirt about during their development. However, it will also soak up any rainwater that a leaky nestbox lets in. A cold wet debris would be sufficient to chill a clutch of eggs so that they don’t hatch, or kill a newly-hatched brood of young.

What’s the solution?

Tree-mounted and pole-mounted nestboxes should be built to a recommended design using treated timber, roofing felt and ‘weatherseal’ sealant for all the joins.

Poor Nestbox Design Outdoor Flat Box     Good Nestbox Design Outdoor Deep Box

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Why is a human access panel necessary?

Barn Owl Nestbox Design Access PanelNestboxes periodically need to be cleared out. This is especially important for deep nestboxes, as each successful nesting cycle reduces the internal depth (each year’s pellets add to the existing debris thereby reducing the safe drop from the hole to the nest). The owlets can then jump up and get out of the hole earlier, and are therefore more at risk of falling.

Why does the nestbox have to be well-built and well-fixed?

Clearly you want the nestbox to last a reasonable amount of time and be safe for Barn Owls during its lifetime. Use good quality materials, build it well and fix it securely, and it should provide a home for Barn Owls for many years to come. When an old nestbox falls down it is often the supporting timbers that have rotted (or nails/screws pulled through) rather than a problem with the nestbox itself. 

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Why is nestbox weight important?

Working at height can be dangerous and your health and safety is of prime concern. The heavier the nestbox the more difficult it is to erect at height, and the greater the chance you will injure yourself or others, particularly if it’s not fixed securely.

Why is nestbox size important?

Our nestboxes are the minimum recommended size for successful roosting and nesting. Anything smaller and there may not be enough room for developing owlets. The size of Barn Owl Trust Barn Owl boxes for use in buildings and on trees are a compromise between what the birds need and what is practical for people to erect by hand. Provided that you can erect them safely, please do feel free to make your nestboxes bigger (and deeper).

Nestbox design criteria

If you are thinking of buying a Barn Owl nestbox (other than from us)  or building one (other than from our plans), we strongly suggest that you check it against these design criteria:

Indoor Barn Owl nestbox design criteria.
Tree-mounted Barn Owl nestbox design criteria.
Pole-mounted Barn Owl nestbox design criteria.

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