|Erecting the Pole-Mounted Barn Owl Box
Once you have determined the best location for your nesting box, dig a hole 24 to 30 inches deep and cement the 1" section of pipe into the hole. Make sure that the pipe is straight. it's a good idea to use a level to check this. To assist in this task, a section of 1.25" PVC may be of benefit; slip it over the steel pipe as an extension to better check alignment.
Once the cement has set you are ready to continue the mounting process. It is recommended that at least 2 persons be present to place the pipe with the box attached onto the standing pipe cemented in the ground as the balance may be a bit precarious for a single person.
If wooden posts are a must, Redwood is preferable, 16 long 6x 6 set in concrete with 3.5 below grade. They should be plumb. Attach the box to the post with lag screws, making sure that the box is level and centered on the post.
To deter predators from attempting to climb up to the nesting box, wood posts should have a 3-foot width of metal flashing wrapped around the base of the post 1 foot above the ground. You may find that it's helpful to number the boxes before they are installed.
Barn Owl Box Location Guidelines
Admittedly, it is difficult to predict with certainty whether a box will attract owls; the best locations are sometimes determined by trial and error. Once most of the boxes are occupied, more can be added.
Barn Owls do not necessarily hunt in close proximity to their nest. Therefore, nest boxes can be placed some distance away from heavily infested areas and strategically placed in overlapping areas. Regardless, placing a perch in an area of high rodent infestation will encourage the owls to hunt in that area. Placing the boxes one hundred yards apart is quite adequate. This should provide sufficient coverage and allow for some territorial behavior by the male.
Boxes may be located near tree lines (within about 100 yards) to provide a nearby perch for young as they venture out of the nest. However, the box should not be too close to dense woods which, in Northern California, are the habitat of the Great Horned Owl and the Red-Tailed Hawk, the Barn Owls primary predators. If you have trees on the perimeter of your vineyards, install owl boxes on the outside of the foliage drip line.
In vineyards, it is best to place boxes between rows at the end of a row of vines, not in the center of vineyards or at the end of vineyard rows. Place boxes on vineyard lanes taking care that there is open space in a five foot radius around the post providing the owl with visibility to immediate hunting ground and for easy access for maintenance.
In vineyards with proximal trees, rodents are often in the uncultivated area between the trees and cultivated crops. The number of owls that can be supported is determined by that area.
Areas to Avoid
Because the flight path of owls is low, large trucks and trains are the number one killer of Barn Owls. Box placement should not be near roads or train tracks that have significant night-time traffic.
Barn Owls, along with many other raptors and different species of birds, commonly die from interactions with power lines, so do not place boxes on or near utility poles.
Owl pellets are highly corrosive to metals, so boxes should not be placed near vehicles or other valuable property.
- Place Boxes 100-200 yards apart
- Face open area
- Mount away from frequent human activity
- Back of box to prevailing winds
- Not too close to dense tree areas
- Away from roads and power lines
- Mount box level to the ground (with bottom of box 12 above ground)
How Many Barn Owl Boxes do I need?
The question isn't: "Will Barn Owl boxes reduce my rodent problem?" it's really: "How many boxes are required to do the job? While the food supply remains dependable, the owls will return season after season. Extra boxes will allow for the natural fluctuation of both prey and Barn Owls. Barn Owl densities of one pair per acre in non-irrigated fields would be necessary to remove the annual reproductive output of gophers.
When spacing owl boxes around the rodent infested areas, keep in mind about four to six boxes will handle 50 light to medium infested acres. UC Davis reports suggest 1 box for every 3 to 4 acres is maximum. Like other birds, owls are collegial, they are not territorial and will share hunting areas. Where rodents are not such a serious problem, the same number of boxes will work for 100 acres.
The biggest mistake a grower can make is to not providing enough sites. Those who have multiple nest boxes in place, find that 40 to 70 percent of them are used by owls, so installing just one box may or may not work. Keeping in mind the success rate of box habitation is about fifty percent, put up two, three, or more boxes to increase your chances of attracting owls. From then on, add one or more boxes each year to keep ahead of the population. When 70% of your boxes are populated, you have attracted all the owls your land will support.
Choice of Mount
The Barn Owl Box is suitable for mounting in trees or structures although pole mounting is more common. Nest boxes can be attached to a tree, a building such as a barn, or a post away from intense human activity. They should face into an open area away from prevailing winds.
Traditionally, Barn Owls have made their nests in trees or buildings although any structure with a hole will do. However, as trees have given way to cleared land, the pole mount has become more popular.. If trees are selected, note that a clear approach path to the box is needed and, as with any mount, the box must be level to the ground.
As noted earlier, mounting the box on a barn or other building is a possibility, but there is evidence that given a choice owls prefer the sites with the least human activity.
There is no need to put any nest material inside the box. The owls will regurgitate pellets, consisting of undigested bones and fur into the box, and the female will create a soft nest for the young by carefully breaking the pellets apart. However, early on, because owls bring in no nest material, you might add a 3/4 layer of wood chips or wood mulch to prevent the eggs from rolling around.