Mice and rodents can carry diseases, some serious to humans. According to the Centers for Disease Control and Prevention, mice and rats directly or indirectly transmit over 20 diseases worldwide. Several of these, such as leptospirosis and salmonellosis, are contagious to animals.
In fields and pastures moles, gophers and other burrowing rodents can just make a mess of things with their telltale piles of dirt and holes everywhere. In summer months can wreak havoc with irrigation and in the winter they will often gnaw on the roots of shurbs such as blueberries and kill the plants - often by chewing right through them.
Rodents are probably one of the toughest things to deal with on properties. They are small, stealthy, and primarily active after dark when we don’t see them. The challenge is can we go about reducing the populations of these persistent little things without lethal trapping or using poisonous chemicals which are deadly to other animals in the ecosystem—as well as to our pets and livestock?
The anwer lies in predators. Some people are concerned that encouraging predators will create risks for their livestock, but properly managed, there is minimal to no negative impact and the positive effect of fewer rodents and their respective damage will fall outweigh any downside.
Barn owls have become very popular to attract for various reasons. Owners of vineyards, orchards, and farms have found that barn owls can significant reduce damage by crop-eating rodents. Property owners can benefit the same way with sometimes no more than one or two nest boxes. Conservationists are finding that erecting owl houses is the best way for bringing back numbers of barn owls in areas where they have declined. And bird lovers simply love having them around to enjoy the opportunity of watching these white-faced, golden winged raptors sail out over a field at dusk on the hunt.
Barn owls are perfectly suited to livestock properties as they hunt in open meadows and grasslands. These creatures of the night have excellent low-light vision, they fly silently, they have sharp beaks and powerful talons, and their hearing is extraordinary. All that makes them death on wings for rodents. A family of barn owls will consume about 2000 mice or other rodents in a couple of months!
One of the ways to help encourage barn owl habitation is by providing nesting boxes and the right habitat for their prey. This is a great project during moths with weather less conducive to outdoor chores.
Barn owls are secondary cavity dwellers. That means they live in the hole that somebody else has created, like a hole in an old tree made by a woodpecker or the dark rafters inside a quiet barn. Storage barns may be better suited than barns that get a lot of traffic. Regardless, humans can take advantage of their desire for secondary cavities because it means that barn owls adapt well to nest boxes which can be purchased or made.
Place a barn owl nest box in a quiet location, 10-20 feet high. Shade the opening from direct sun and prevailing winds. Boxes can be hung inside an unused barn, on the outside of farm buildings, on a pole or in a tree. If the box is mounted on a pole or post, consider a baffle to prevent cats, raccoons, and other predators from reaching it. Many barn owls will reuse the same nest box year after year. In North America it is best to hang them by January or February as barn owls begin nesting in late February. When selecting a tree location, you will also have the benefit of selecting the most advantageous sideof the tree.
It’s hard to find an easier method of rodent control. Once you install the barn owl box nature does the rest. Plus, barn owls are not aggressive to people, nor will they attack pets or livestock. Not only will owls help reduce your rodent population, but their tawny colors are beautiful to see at dusk and their bone-chilling, screechy cry is thrilling to hear at night.
Building the Nesting Box
The popularity of attracting barn owls has resulted in a wide range of barn owls box designs, both do-it-yourself and those that are sold commercially. It is important to take into account the biology and daily needs of these large owls. With so many versions of nest box to choose from, some excellent, some not so good, it is important to make wise decisions about which elements are ideal for successfully attracting and housing these beautiful raptors.
1. Appropriate Size: Make sure your box is big enough. Many barn owl box designs create a nest box only 18” deep. Although this size can attract a breeding pair, barn owls produce an extraordinary number of young—seven is quite common. The entire brood of owls must reach adult size inside that nest box before fledging, each of them 12 to 14 inches high, and flapping their wings in preparation for flight. In small boxes, flight feathers are damaged, smaller birds will not receive food, and young birds are pushed accidentally from their nest boxes - weaker ones may be intentionally pushed out. In short, fewer birds survive from such owl houses.Takeaway: Select designs that are at least 24” deep, 18” high, and 18” wide.
2. Size of Entrance Hole: Conversely, many designs err on making the size of the entrance hole too large. All cavity nesting birds, including barn owls, prefer an entrance hole that is just large enough for them to squeeze through, but too small for larger animals that might prey on the eggs or chicks. Barn owls vary in size. Like all predatory birds, femails are typically 30% larger than males and American barn owls larger than those in Europe. Takeaway: Takeaway: The box should have a 5” to 5 ½” entrance hole.
3. Location of Entrance Hole: Holes too close to the floor are a problem because the ever curious and rambunctious chicks tend to crowd toward the entrance hole as they get older. A hole too close to the floor allows for them to fall out way too early. Takeaway: The entrance hole at least six inches off the floor.
4. The perch: Don't forget the owls will like some sort of "front porch". This can be as simples as a dowl or a full ledge where the owl can rest and feed.
5. Color: Many wooden boxes are left natural to blend into the environment. The problem is that most wooden boxes are heat traps. As the sun beats down on dark wood, the interior can become excessively hot. Biologists have found young owls, too young to leave the nest, on the ground where they took refuge from the stifling heat inside wooden boxes. Also, consider your location selection - again, away from direct sun, wind and rain. Takeaway: If you do buy or make a wooden box, be sure to paint the entire outside with bright white paint to reduce heat absorption and plan to repaint every year or two.
6. Material: Most commercially made boxes and available plans use half-inch plywood. The problem with such thin wood is that, after the expense and labor of construction and installation, half inch plywood deteriorates rapidly in sun and rain. The alternate choice, ¾ to 1” plywood will last somewhat longer, but it is heavy, expensive and difficult to install. So, when it comes to plywood owl houses, the choice is between longer life and ease of installation. Takeaway: If you are buying a wooden box, ask the builder the thickness of the wood.
The Final Summary
Published in the Journal of Pest Management, Newport Beach, California: From 2011 through 2013, researcher Mark Browning and a team of students from U.C. Davis and Columnes River College saturated a 100-acre vineyard south of Sacramento, California with 25 barn owl nest boxes, eventually resulting in a population of 36 adult owls that fledged 66 young. This produced a population of 102 barn owls hunting the vineyard and surrounding area. Using data gleaned from nest box cams, the research was able to conclude that this rather incredible density of owls consumed 30,000+ rodents over a 3 year period. Statistical analysis showed a strong correlation of number of owls to a decline in rodent activity. This study is the first of its kind to accurately record the number of rodent deliveries to growing barn owl chicks, and the first to establish the economic value of barn owls to farmers and property owners. Cost comparison data showed that the average cost of trapping per rodent was $8.11 while the nest box program resulted in a cost of .27 per rodent taken by barn owls. This provides very valuable and useful information for farmers to use in assessing the effectiveness and results of barn owl nest box programs.