HOW MANY DO I NEED
The question is 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. If all of your boxes are full, you can add new ones.

It’s recommended that when spacing the boxes around the rodent infested areas, about four to six will handle 50 light to medium infested acres, or about 1-2 boxes for every 10 acres. UC Davis reports suggest 1 box for every 3-4 acres is maximum. Keep in mind that the birds 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 the birds, 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 some. 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.