The important elements of a barn owl nest box are roominess (to accommodate the species’ large broods) and seclusion from predation. although barn owls have used oddest of designs, the style shown here has proven successful when placed in a variety of situations. If placed up beneath the barn’s roof, there is no need to put a roof on the box. If placed lower in the barn or in an open-topped silo or tree, a roof must be installed to provide the necessary seclusion and protection from weather.
Construction is simple. The sides are first fastened to the front and back and then the bottom is attached. If a top is used, it should be put on after the box is installed to facilitate easier nailing. Use exterior plywood if the box is to be placed in an exposed situation. Approximately nine drain holes, 1/4-1/2 inch in diameter, should be spaced throughout the bottom. Cover the bottom with one or two inches of wood shavings, as barn owls place no nest material.
Barn owls prefer to nest in buildings, and boxes should be installed high to lessen human disturbance and the dangers of predation from snakes, raccoons and cats. If placed in a barn, the front should face into the barn. The back can be nailed flat to the barn. Usually, a brace or stud can be located on which to secure the box firmly along one side. Metal straps attached on the back can be bent to hang the box in a barn or inside a silo. In some regions, barn owls use boxes that are simply wired in place high in a large tree.
The most productive site for a barn owl box is where individuals have been seen. Due to the species’ rarity, the possibility of attracting them in other areas is remote but worth a try. The best localities are rural. Areas where there are open grasslands and crop fields and where grain spillage results in high mouse populations are especially suitable for nesting barn owls.
Barn owls are permanent residents and may nest at any season. Their clutch of five to ten white eggs will produce a varying number of the young, depending on availability of prey. Incubation requires three weeks. The young, which vary in size due to their hatching dates, fly at about seven weeks of age. Barn owls often nest in the same site repeatedly.
Barn owls are considered to be our most beneficial owl, owing to their appetite for animal pests. One once was observed delivering 16 mice, three gophers, a rat and a squirrel to a nest within 25 minutes. An endangered species in Missouri, the barn owl is found worldwide, nesting almost totally in buildings in the Old World and in hollow trees and burrows in much of the western United States. In Missouri, they utilize a variety of sites. Throughout much of its range, the barn owl’s numbers are thought to be limited by the availability of suitable nest sites.
Should the beautiful, monkey-faced barn owl accept your box, you will be among the fortunate few. You should reduce human activity near the site and discontinue the use of rodent poisons.