Raptors - falcons and owls - that live in Colorado are declining because of habitat loss. Even when hunting habitat is available, the lack of next sites can be a major reason for non-productivity. Old, dead trees provide the best natural sites for cavity nesting birds. They are often felled by landowners. Even our recent energy crisis, which put emphasis on wood burning stoves, could have an impact on all species of hole nesting birds. Where sites have been destroyed in the past, artificial nest sites are a good way for maintaining, or even increasing the populations of cavity nesting birds.
Hole nesting raptors in Colorado such as the Barn Owl, Screech Owl, Boreal Owl, Saw-Whet Owl, Flammulated Owl, and the American Kestrel do not build nests of their own. They rely on natural sites or those created by other birds or animals. Man made nest boxes will be readily accepted if properly constructed and erected. Many times Barn Owls, Screech Owls, and Kestrels will not only inhabit these man made “condos” year after year, but may stay year around in close proximity to the boxes. They are very interesting species to observe and will control the rodent population in the area.
Many different types of nest boxes have been tried. Our designs are simple, functional and can be made by anyone with tools found around the house. Except for entrance hole size, dimensions and placement, the dimensions are not critical and can vary somewhat.
Breeding failures in artificial boxes can occur from predation, too much disturbance and competition from other species. If the box is properly erected and monitored these problems can be eliminated to a certain degree. Barn Owl nest boxes should be safe from raccoons or cats. Starlings often move into Kestrel houses and may have to be “evicted” in the spring.
The number of boxes that can be placed in a given area is limited only by how many you are willing to build. Most raptors will defend their territory, especially during breeding time. The size of the area they defend depends on the species of raptor, availability of prey and other factors. Barn Owls, Kestrels, and Screech Owls have all been found within a one-acre area. Barn Owls sometimes live very close together since they are very gregarious to begin with. One Barn Owl box per silo or barn is enough and 2 to 3 Kestrel boxes spaced between a one or two-acre field is adequate. But, if more boxes are provided, the better the chances of some being found and used.
Materials and General Instructions
For boxes erected outside the best materials are 1″ thick rough-cut western cedar, cypress or redwood. All these withstand weathering. Boxes, which are placed inside buildings, can be made of less expensive pine or plywood. If a wood preservative or paint is used, apply it only to the exterior of the box. When constructing closed boxes, the size of entrance holes and their height above the floor of the box are important and the dimensions given should be used. Proper hole size and placement will allow the birds to come and go freely and still keep a raccoon from entering or reaching the young.
Closed boxes should have the roof, or one side, hinged, providing access to the inside for cleaning and maintenance. Roofs can be shingled for added protection from the weather. Be sure nails and screws used in construction do not protrude inside the box. Generally, boxes should be mounted so the holes face southeast. In new or freshly cleaned boxes a layer of pine shavings should be applied to the floor which will help contain the eggs and make incubation easier. Use only a one-inch thick layer, no more, as eggs can get lost in shavings that are too deep. DO NOT use cedar shavings or sawdust. If ingested along with food, cedar oil can be dangerous and sawdust can be harmful to nostrils and eyes of the young birds.
For any nest box to be successful there are a few requirements which must be met regarding where and how the box is placed. First, proper habitat of each raptor must be chosen and within that habitat the proper type of nest box supplied for that bird. Barn Owl boxes will not be productive if placed in a wooded area. Barn Owls do not hunt or nest in woods, but are birds of open country. So it is important to know something about the lifestyle of each raptor we are dealing with.
Let’s then look at each individual species, see where it lives, what type of nest box it requires and how and where to place the boxes.
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