Before installing a barn owl nest box be sure the property is appropriate. Barn owls need open areas, like fields and meadows, in which to hunt. In urban areas barn owls can do well as long as there are hunting grounds nearby, like parks, ballfields, golf courses.
Avoid placing a box close to power poles or other dangerous prominent objects.
The nest-box should be mounted at least 12' off the ground, on a wooden post, the exterior of a building, a large open tree, or, inside an open building, like a barn.
Attach metal flashing to posts or trees where predators might try to climb and access the box.
Placement and Orientation
Ideally the nest box should be situated near one or more large trees for the parents to roost in and from which fledglings can begin to explore their world.
The entry hole should face away from prevailing winds and north to north east if possible. The ventilation gap should be on the leeward side.
The position of the entry hole (right or left of center) and the ventilation gap will be dependent on the site. We recommend selecting the site first before building or purchasing.
Form and Function
We have done extensive research on barn owls and various nest-box designs and have developed minimum standards based on our finding. The most critical elements are:
Overall size. Research indicates 10 ft.³ should be considered the minimum amount of interior space. Anything smaller risks complications associated with overcrowding, including nest abandonment or injury or death of one or more young.
Our studies have shown a female will remain in a large spacious nest box tending to her chicks until the youngest is about 3 1/2 to 4 weeks old and able to swallow whole prey. Females in smaller, cramped quarters have been documented leaving prematurely, resulting in the death of the youngest chicks.
In example, we documented overcrowding in a box based on the popular Simmons design (23" x 12" x 16") which resulted in the chicks suffering further damage and hawk and foot injuries. The youngest was found deceased.
The owls need room.
When there is enough room, the male may choose to roost (by day) in the nest-box with the female and young.
When there is enough room, the female will move off and away from her eggs and or chicks to groom, stretch, and defecate. We have documented week-old chicks exhibiting similar behavior - to move away from the nest to defecate. Smaller, confined nest-boxes do not allow for this.
When there is enough room, owlets have the space they need to jump about and flap their wings, exercising their flight muscles. They cannot do this in a small box.
Placement of the portal. The entry hole should be situated about 2" from the top of the box and no less than 16" from the floor.
At a certain stage, owlets begin food-begging at the portal, eager for the parents to return with a meal. If the entry hole is too low, chicks can accidentally fall or get pushed out.
Placing the hole at least 16" from the floor will help keep the chicks safe until they have lost their squab-like density and have developed flight feathers.
It's important to add 1/8" grip-grooves to both the interior and exterior of the box, just below the portal.
Additional grip-grooves should be added to the top left and right side of the entry to assist young owls returning to the nest-box after fledging.
Size of hole. The portal should be about 6" - 6 1/2" to make it easier for the owls to get in and out. We have knowledge of an adult owl getting stuck in a hole that was too small (Simmons').
Temperature control. In general, the nest-box should be painted white to reflect sun and heat. In moderate climates a ventilation gap at the top of the leeward side can provide decent airflow.
In warmer regions where the average temperature exceeds 80° for extended periods of time and where the box will receive direct sun for most of the day, we suggest enlarging the ventilation gap to about 1 1/2" and adding a few vents at the base of the sides, approximately 6" from the floor.
In locations where the box receives direct sunlight and the average temperature is 85°, we recommend sun-shields, which are simply additional pieces of plywood attached to the top and sun-exposed side(s) creating a 2" gap between the box and the shield.
Drainage. There should be at least a dozen 1/2" holes in the floor of the box.
Our nest-boxes are constructed using one sheet of 3/4" exterior grade plywood (ACX labeled Exterior - not Exposure 1). Please used FSC approved plywood where available.
We recommend using 2" deck screws and gorilla glue to assemble the sides with a pine or redwood 2 x 2 frame. Crown staples (1/4") can also be used.
The exterior and exposed edges can be sealed with a water-based weatherproofing stain or exterior paint and primer. Use light colors in warm sunny locations.
We recommend installing the nest-box on a 20' pressure-treated 6 x 6 post, set 4' - 5' in the ground. The box should be bolted to the side of the post, not the top.
See our installation video, HERE.
Bedding is optional. We use pine shavings or natural fir bark. DO NOT USE CEDAR, HAY OR GRASS.
Active nest-boxes should be cleaned annually in the fall, between late September and mid-November. Be sure to use the appropriate level of protective equipment, like a respirator mask to reduce risk of exposure to disease pathogens and irritants.
The Global Owl Project