Build a Barn Owl Box for Small Rodent Control
Build a Barn Owl Box for Small Rodent Control. Photo: Marco

Worldwide, it is estimated that small rodents (mice, rats, and voles) are responsible for the destruction of about 35% of the total world agriculture. Small rodents also carry diseases. Some species of small mammals carry the Hanta virus, which can be transmitted to humans. In the first few months of 2014, the Hanta virus has been responsible for the death up to 15 people in the country of Chile. In the United States, 624 cases of Hanta virus infections have been reported in 34 States as of July 9, 2013. The virus can be fatal to humans, but apparently, does not affect owls. To combat rodents, farmers use rodenticides. However, these pesticides are relatively ineffective as they are short-lived and have to be re-applied frequently. Moreover, rodents become bait shy over time. In addition to being ineffective, rodenticides destroy ecosystems, poison the soil and water systems and have secondary health effects on humans and wildlife.

Barn Owls as a Bio Control Agent

Barn Owl Box for Small Rodent Control
Owl nesting boxes need to be cleaned after every nesting season. Photo: Grefa.

Attracting barn owls (Tyto alba) as a bio-control agent has proven to be highly effective in reducing small rodent populations. Predation upon rodents by barn owls substantially decreases rodent numbers, thus lowering crop damage and eliminating the need to use rodenticides. This approach helps create a sustainable environment for both humans and wildlife. Barn owls are good candidates for Integrated Pest Management in Organic Farming. Their voracious appetites and large broods make them effective in controlling rapid population growth of rodents. Barn owls will often raise more than one brood per year in response to higher rodent (food) availability.

A researcher in Malaysia determined that using barn owls in oil palm plantations significantly reduced the need (and expense) for poisons. It was estimated that ten barn owl families consume about 15,000 to 20,000 rodents per year. The good news on this is that establishing an owl population in most agricultural settings is not difficult, and the beneficial effects are substantial.

It was estimated that ten barn owl families consume about 15,000 to 20,000 rodents per year.

California vineyards are attracting owls to control pocket gophers. Because vineyards are increasingly moving toward organic farming techniques, they are finding barn owls to be excellent at helping with rodent control. Other types of agriculture, including pecan, walnut, and citrus groves are finding barn owls to be useful additions to sustainable agriculture.

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Barn owl taking a mouse to its chicks in a box nearby.
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Barn owl nesting box in sugar cane plantation. Photo: Richard Raid.

Population of small rodents in sugar cane plantations can cause tremendous damage to a sugar cane crop. In Florida, barn owl nest boxes have been erected in sugar cane fields for years. When small rodents grow in numbers, barn owls also attain great numbers and the owl’s effect in controlling small rodents is amazing. Owls in South Florida’s sugar cane plantation reach such numbers that unlike the norm, they day-roost in trees due to the lack of available structures. Some of the Australian pines patches had over 18 owls during our visit in July 2013.

Fighting Disease with Barn Owls

This year the Hanta virus has already caused 15 deaths in Chile, according to reports in The Santiago Times. While the virus is not always fatal the 15 deaths were of a total of 36 cases over six months a the end of 2013 and beginning of 2014. The Chilean government is using a novel method to fight the disease; owls.

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Owl pellets and mice stored in a barn owl nesting box. Photo: Grefa.

A government campaign is working to encourage owl species such as barn owls and the Magellenic horned owl (Bubo magellanicus). The idea is that by providing more nesting and breeding sites for the owls they will have more opportunities to mate and breed, increasing the population and thereby reducing the rodent population through predation. This entails building simple wooden boxes that serve as nests for the owls. Boxes were installed in the conservation areas, public lands, and as close to human populations as possible for the owls to be more effective.

On and interview with mongabay.com, Moises Grimberg, director of Chile’s biodiversity and conservation department stated that “Given the success we have had by providing nesting opportunities for owls, we consider the owl program to be a useful natural method to help control disease-carrying rodents. This success story has prompted the replication of this idea in other parts of the country. Interestingly though, owls are associated with bad omen in most of Latin America.

This belief presents a hurdle between the general public and the adoption of such idea. Some considerations when thinking of attracting barn owls.

Owls are associated with bad omen in most of Latin America.

Barn owls are cavity dwellers and are happy to nest in almost any snug and quiet spot, be it the crook of a tree, the rafter of a barn, or a manmade box on a pole.

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Barn owl nesting on a window sill. Photo: Las Nubes Vinedo.

So long as the food supply is ample, barn owls are not too territorial and may even nest in colonies.

  •  To be attractive to the birds, owl boxes should be placed at least ten feet off the ground. But don’t place the boxes so high that they become difficult to maintain.
  •  Be careful not to startle parent owls during the incubation period. If a mother owl is frightened away from her nest before the eggs hatch, she may not return. Once the baby owls hatch, however, parent owls will return to feed their young, regardless.
  • Barn owls are wild animals and a protected species. Although providing nesting sites for them is perfectly legal, you must be licensed if you want to handle them. Contact the U.S. Fish and Wildlife Service for information and restrictions.
  • Debris in owl nest boxes can be infected with the Hanta virus. Take precautions such as using rubber gloves and dust masks when performing maintenance or cleanup.
  • The project is based on the erection of large numbers of nest boxes in farmland (typically spaced at 200 – 400 metre intervals), a decrease in the use of pesticides, and creating a friendly environment for raptors in general.
  • You must never use any rodent poisons on your property, and it’s a good idea to talk to your neighbors about that as well. When rats or mice or gophers eat poison, it takes them several days to die. During that time they become weakened and thus easy prey for the owls. The poisoned rodent will then poison the animal that eats it. One poisoned mouse brought home to feed baby owls could wipe out the whole nest.

Barn Owls and their young can be quite noisy during the breeding season, which lasts about four months, consider that before placing a box as you cannot remove the box once the nesting begins.

Build a Barn Owl Box for Small Rodent Control

Barn owls are happy to nest in almost any snug and quiet spot, be it the crook of a tree, the rafter of a barn, barn-owl-nesting-box-or a man-made box on a pole. Boxes offered to barn owls vary in size and shapes, but the birds appear to take them all equally. I present two nesting box designs proven to attack barn owl.  The design to the right is simpler. This is the box type used in the sugar cane plantations in South Florida.  This design is also widely used in Latin America with favorable results.

Another barn owl nesting box design was created by Steve Simmons and has been used with favorable results in many places in the United States. Mr. Simmons owl box has been in extensive use since 1995 in California. Specific instructions to build a barn owl can be found following this link.

Step by Step Instructions to Build and Barn Owl Box