Many species of raptors–hawks and owls–that live in New Jersey have declined in numbers because of habitat loss. Within the habitat that remains, cavity-nesting raptors cannot find suitable places to breed.
Even when hunting habitat and prey are available, the lack of a nest site can be the major reason for the non-productivity of a hawk or owl species in a given area. Old, dead trees, which provide the best natural sites for cavity-nesters, are often the first to be felled by landowners. Whenever possible, we should try to preserve existing nest sites. Where sites do not at present exist, or have been destroyed, furnishing artificial nest sites is a feasible method for maintaining, or even increasing, populations.
Cavity-nesting raptors such as Barn Owls, Screech Owls, Barred Owls and American Kestrels do not build nests of their own. They rely on natural sites or those created by other birds or animals, including humans. All these birds will accept man-made nest boxes. When properly constructed and erected these raptor “bird houses” are readily inhabited and may be used year after year. Barn Owls, and to some degree Kestrels and Screech Owls, not only use these boxes but have adapted to man so well, that many spend their entire lives in close proximity to their human landlords. Attracting these birds is desirable not only for their ability to control rodents, but because they are interesting species to have close by for observation.
Many different types of nest boxes have been tried. The designs proposed here are simple, but functional, and can be made by anyone with tools found in most homes. Except for entrance hole size and placement, dimensions are not critical and may vary an inch or two one way or the other. You need not be a bonafide carpenter to construct a house any hawk or owl would be proud to live in. These designs are by no means the only acceptable ones but from experience, I can say these work.
Breeding failures in artificial boxes from predation, too much disturbance, and competition from other species can be minimized if the box is properly erected and monitored. It may be difficult to place a Barn Owl box in a silo or barn where it will be safe from a raccoon or cat, but this effort must be made to insure success. Starlings and Kestrels compete for nest sites and you may have to “evict” a few sturnus vulgaris from your newly erected Kestrel box 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 breeding territory and not allow others of their species to occupy that territory. The size of the area they defend varies depending on the species of raptor, availability of prey and other factors. I have found Barn Owls, Kestrels and Screech Owls all living in fairly small areas, occasionally all three species within one acre. Also on three adjacent farms I have found three Barn Owl families living within sight of each other. One owl box per silo or barn is enough and two or three Kestrel boxes spaced within a one or two acre field is adequate. But, within reason, the more boxes provided, the better the chances of some being found and used.
For boxes erected outside the best materials are 1″ thick rough cut western cedar, cypress or redwood. All these will 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 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. For instance, even a well constructed Barn Owl box 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.
Barn Owls live and breed throughout the entire state. Most are migratory, but some birds remain resident year around. They are birds of open terrain, hunting in fields, meadows and farmlands. It is not uncommon to find Barn Owls living in parks, deserted lots and along railroad tracks. These raptors, more than any others, spend their lifetimes in close proximity to man.They nest in a wide variety of places including church towers, farm structures, semi-derelict (and often occupied) buildings, water tanks, under bridges, on drive-in movie screens and in silos and barns. Many potential nesting sites already exist and may only need slight modifications to allow Barn Owls to utilize them. Often, simply affording the birds access by unscreening a window, removing a slat from a steeple, or poking a hole here or there, will create an acceptable site.
Erecting nest boxes not only increases the available breeding sites for resident birds, but may attract birds into areas where they have not bred before. It may take a while for the box to be discovered and used, but not always. Two years ago in early June I installed a box in an unused silo where Barn Owls had been roosting. Three weeks later an owl was in the box, incubating eggs. She must have been waiting for me to show up with her nest.
Two designs work well for Barn Owls. The open tray type is the easiest and least expensive to construct. This type should be used inside a barn. silo or other building where a roof or covering already exists. Place the box high in the structure where it will be inaccessible to house cats, raccoons, or too much human disturbance. The box can be nailed fast or hung with rope, wire or brackets.
The closed box type can be used in a topless silo, attached to the outside of an existing structure, erected on a pole or placed in a tree. When erecting on poles or trees remember to choose open areas, fields, meadows, etc. and face the entrance hole south.
New Jersey’s resident falcon, the American Kestrel, and our smallest breeding owl, the Screech Owl, occur statewide. Kestrels are resident throughout the year although some migrate. Screech Owls are basically non-migratory and remain in the same areas all their lives. The habitat in which both birds live is similar and the best boxes made for them are identical.
Kestrels are birds of open terrain, seldom entering woods. They hunt fields, shorelines, meadows, roadsides and other open areas. They are regularly seen perched atop telephone poles and utility wires or hovering in mid-air, searching the ground below for prey. Boxes should be placed in open spaces. Good locations are: trees along the edge of a woodlot, a lone tree in a field, on a barn or other farm building, or mounted on a pole. Constructing your own pole offers the advantage of being able to place the nest box anywhere. Open fields and meadows afford the hawks proper habitat to hunt mice, moles and their summer favorites–grasshoppers.
Boxes should be placed 12 to 20 feet above the ground. When using a pole or post for erection, a metal sleeve 30 inches wide should be wrapped around it and secured, to keep mammal predators from climbing to the box.
Screech Owls live in open woodland terrain. They are found not only in open country, but in lightly wooded areas, city and rural parks, small woodlots, and a particular favorite – apple orchards.
This is not a common owl in New Jersey, but occurs rather locally throughout the state. Its status is officially listed as “threatened” (may become endangered if conditions surrounding the species begin or continue to deteriorate). Barred Owls are birds of dense wooded swamps and deep forests. Woodlands which border lakes, streams, marshes, or swamps are favored. The woods may be deciduous or coniferous, or mixed. They are sedentary owls and permanent residents in New Jersey.
Barred Owls almost always nest in hollow trees. They are large owls and require large cavities in which to breed. The decreasing number of such natural sites, plus the very specialized habitat requirements of this bird, have caused its numbers to diminish drastically.
Historically, most artificial nest boxes for raptors have been built for Barn Owls, Screech Owls and Kestrels. To my knowledge, very few nest sites have ever been provided for Barred Owls. It may not be possible to expand the distribution of this species to any great extent, because of its habitat requirements, but supplying boxes in areas where these owls do exist could be highly beneficial in maintaining or even increasing their populations. It would be a worthwhile effort on our part to assist this beleaguered bird in any way we can.