Integrated pest management is a science-based pest management process that focuses on ecosystem management for the long-term prevention of pests and the damage they cause.
The University of California Division of Agriculture and Natural Resources has developed an IPM program dedicated to helping Californians “prevent and resolve pest problems with the least amount of unintended impacts on people and their environment.” For the home gardener, a guiding principle of IPM is to understand why your landscape favors particular pests, and then adopt changes that will make that environment less attractive to those pests.
One element of the IPM approach is to use biological control measures rather than pesticides to reduce garden pests wherever possible. This usually involves creating conditions that attract the pests’ natural enemies. For rodent control, owls are an often overlooked ally of home gardeners and farmers.
According to the Altacal Chapter of the Audubon Society, 10 different species of owls can be found in Butte County. Of these, eight are permanent residents: the barn owl, the great horned owl, the eastern screech-owl, the little owl, the burrowing owl, the spotted owl, the short-eared owl and the short-eared owl. Since most owls are nocturnal, they are not easily seen in the wild, but birders often recognize different species by their distinctive calls. The National Audubon Society has a website with recordings of calls from different species of birds, including owls: https://tinyurl.com/ucbcmg-owls. I’ve never seen them, but I regularly hear great horned owls and spotted owls around my home in the foothills above Oroville.
All animals have three basic needs: food, water and shelter. In the case of owls, their food (mostly rodents) is already present in most settings, whether wild, rural, suburban, or urban. Owls also get the water they need from their prey. Providing shelter is the only thing a landowner can realistically do to attract owls as a method of rodent pest control. Shelter for most owls consists of rotting hollows in trees or artificial nesting platforms and nesting boxes.
Birdhouses are commercially available but can be expensive. For the do-it-yourselfer, birdhouse plans for various owl species are available free from the Cornell Lab of Ornithology, https://nestwatch.org/learn/all-about-birdhouses. The roof or one side of a nest box should be hinged to create a door that can be opened for cleaning after the owls have fledged and left the nest. Quarter to half inch holes drilled near the roof will aid in air circulation and similar holes in the floor will allow for drainage if needed. Spread wood shavings or shavings on the floor of the box for bedding. The box should be placed at least 15 to 20 feet above the ground with the opening facing northeast.
Owls regurgitate the undigested fur and bones of their prey as pellets. Pellets and feces will accumulate inside the nest box, so owl nest boxes should be cleaned at least once a year, after their occupants have left. The best time to clean the boxes is from October to December. Be sure to avoid breathing in the unhealthy dust when cleaning a birdhouse.
Owl safety is a consideration when deciding if it is appropriate for you to attract them to your property. Do you have any high speed roads nearby where owls could collide with vehicles? Do you or nearby homeowners regularly use pesticides, herbicides or other potentially harmful chemicals? As predators, owls are particularly sensitive to these chemicals because they often become more concentrated as they move up the food chain. Additionally, the light pollution produced by the porch and outdoor lights can be confusing and a deterrent to these nocturnal hunters.
It is important to preserve tall trees because most owls prefer mature trees for roosting, hunting and nesting. Dead snags can provide nest cavities, but can be dangerous in fire areas.
Finally, consider pets. A hungry owl could feed a small dog or a domestic cat. (I sneakily suspect the great horned owls are the reason our local feral cat population was brought under control).
The natural habitat preference of a particular species of owl will help guide the decision on which species to attract. Four owl species found in Butte County with varying habitat requirements are good examples of how habitat influences owl distribution: barn owl, great horned owl, burrowing owl, and barn owl western scares.
When Humboldt State graduate student Carrie Wendt studied the nest site preferences of barn owls, she found that they preferred nest boxes near grasslands, riparian and mixed forest habitats as opposed to mixed brush. Therefore, efforts to attract barn owls to heavily forested areas are likely to fail.
Barn owls are medium-sized owls, with adults measuring 13 to 16 inches and weighing between one and one and a half pounds. They typically hunt within 1-3 miles of their roost and are only slightly territorial, so you can set up multiple nest boxes in an area with possibly multiple families settling in. Horned owls are the fiercest predators of barn owls, while collisions with cars are also a major contributor to the barn owl’s death toll.
Barn owls seem to be the go-to owl in rodent pest biological control, dominating the literature on owls and IPM. According to several studies, pocket gophers, mice, and voles make up the bulk of the barn owl’s diet. In fact, 99.5% of the prey studied were agricultural pests, so it’s clear that owls can provide valuable pest control services to farmers.
According to UCANR, a family of five barn owls, including two adults and three young, will feed on about 1,000 rodents over the course of a season. Because they prefer to hunt in more open areas, they happily hunt in vineyards, alfalfa fields, and along dykes, making them valuable allies for farmers practicing IPM. Over a three-year period, one study found that barn owls killed more than 30,000 rodents in a single vineyard for a fraction of the cost of trapping or poisoning: “the average cost of trapping was 8.11 $ per pocket gopher versus $0.34 per rodent taken by barn owls.
On the other hand, great horned owls prefer to nest in wooded areas with scattered clearings. In the wild, they nest in old hawk, magpie, raven and crow nests, so they are more likely to be attracted to an artificial nesting platform or nesting basket rather than a nest box.
Growing up to 2 feet tall, weighing three pounds, and with a wingspan of nearly four feet, this huge and powerful bird is the tallest owl in North America. It gets its name from the tufts of feathers (“horns”) that protrude from its head. Ferocious predators, they will hunt prey weighing up to 15 pounds, including rabbits, grouse, and skunks (and pets!), as well as smaller prey such as squirrels and mice. Great horned owls will chase and kill all other owls, so do not place great horned owl nesting baskets near other owl boxes.
Burrowing owls have always preferred to nest in grasslands and grasslands – areas with short grass or exposed ground where they can dig their burrows. Today, they are also found on farms, golf courses, wastelands, and even airports. Unlike other owls, burrowing owls nest in underground burrows and these types of open spaces make it easier to build burrows.
These owls often commandeer and enlarge burrows dug by other animals. Homeowners who can provide this type of habitat can further encourage burrowing owls to make their home by providing an artificial burrow that these owls can complete.
Once called “birds” by cowboys because of the rhythmic nods they make from the entrance to their burrow, these little owls reach a height of just nine inches and weigh only seven ounces. The burrowing owl feeds on small birds, reptiles, large insects, rodents and even fish. Although they hunt somewhat at night, burrowing owls are diurnal, meaning they are active during the day, an uncommon pattern for an owl.
Another small owl, the Eastern Screech-Owl ranges in size from seven to ten inches and weighs between three and a half and eleven ounces. Western spotted owls have a varied diet that includes everything from worms and crayfish to rats and bats. They will even take prey larger than themselves, such as cottontail rabbits or mallards. Although they are daring hunters, if they get scared, these masters of camouflage will elongate their bodies and constrict their feathers to resemble the end of a branch.
The natural habitat of western spotted owls is open forests, where they nest in tree cavities, but they can also be found in urban parks and residential areas. Because they readily occupy backyard nest boxes, they are probably the most likely owl candidate to be attracted to a suburban homeowner in their yard.
Owls can be a valuable ally for farmers and homeowners who want to practice biological pest control. With a little research and relatively minimal effort, they can be encouraged to settle near you.
The UC Butte County Master Gardeners are part of the University of California Cooperative Extension System, serving our community in a variety of ways, including 4-H, agricultural counselors, and nutrition and health programs. ‘physical activity.