Story and photos by Paul W. Wilson
I was a high school science instructor for 26 years and sponsored science clubs at the schools where I taught.
One of the most interesting projects involved building habitat for barn owls in Oklahoma. This project started in the 1980s and continued through 2001.
With a major change in hay storage starting in the 1970s, lofts in barns became obsolete. Previously, hay was in small “square” or “round” bales approximately 80 to 100 pounds each that were stored in lofts or protected areas. Since the 1970s, hay typically has been in very large round bales of 800 to 1,600 pounds each that are stored in bale yards or in open barns. In some areas, large square bales are used and are stored similarly to round bales. Barn owls thus no longer can find hay-filled lofts for their nests.
My science club students and I built hundreds of nesting platforms to be inserted into abandoned buildings for safer nesting for barn owls. Barn owls’ primary predators are raccoons, opossums, and snakes that eat the eggs, young owls, or even adult owls if the stay in the nest — most commonly raccoons. Many of the barns were built from about 1900 through the 1960s. Since then, very few barns have been built with lofts, and in the Oklahoma weather, many older barns have collapsed over the years.
So the Owasso Science Club and I came up with a design for an artificial nesting house. We built 10 Type 1 houses with funds from the Oklahoma Department of Wildlife Conservation in 1990. We discovered that the houses had design flaws, so we developed a much stronger design with interlocking walls and stronger materials. The Owasso Science Club received a TAPESTRY grant from Toyota to build 25 Type 2 houses with the new design in 1995. The projected life of the Type 2 design is 40-plus years.
We located the nesting houses in areas where there were no nesting structures
with barn owls resident. Some of the houses were near barns with nesting pairs, but the barns were not expected to survive Oklahoma weather much longer.
Facts about Barn Owls
Common barn owls (Tyto alba) or American barn owls (Tyto furcate) are most numerous in southwestern Oklahoma and least numerous in southeastern Oklahoma. The American barn owl has 19 subspecies resident in South, Central, and North America, with very limited distribution in the north-central United States. American barn owls are not present in Canada.
The estimated number of American barn owls in the United States is 140,000. During the mid-twentieth century, the population of barn owls declined because of wide use of DDT. In the late twentieth century, bioaccumulation of rodent poison in the prey species contributed to the decline of barn owls in some areas. The population of barn owls is still under pressure from habitat destruction and collapse of old barns and abandoned structures.
Normal weather patterns have a stabilizing impact on the population of barn owls, and extreme wet or dry conditions have an adverse effect. During flood
conditions, the prey species drown or become concentrated in small pockets that predators destroy. During extreme drought conditions, the prey species are reduced, and the survival rate of young owls is reduced.
When rodents are not available, the owls supplement their diet with birds, and the adult owls are in jeopardy at that point. In extreme cases, which have been observed only twice in 55 years, barn owls will eat grasshoppers. At that point, the owls will die if they remain in the area; they cannot digest the protein in the exoskeletons.
Female barn owls are approximately 33 percent larger than males, which is common in birds of prey. The length of the body is approximately 21 inches, with a wingspan of 47 inches. Females weigh 24 ounces, and males weigh 20 ounces. Their body temperature is 103 degrees Fahrenheit. The sexes of barn owls look the same except for the breast feathers — tan for the female and white for the male.
Barn owls are the only owls in Oklahoma that are considered Old World owls; others are considered New World owls. Barn owls locate prey primarily by sound, and other owls primarily use vision. Owls have silencers on the leading edge of their wings for quiet flight.
Barn owls normally eat their prey whole and regurgitate a casing, or pellet, each day. The pellets contain the bones and fur of the prey species. The most common prey species in Oklahoma are hispid cotton rat (Sigmodon hispidus), prairie vole (Microtus ochrogaster), hispid pocket mouse (Perognathus hispidus), and deer mouse (Peromyscus maniculatus), but many other rats, mice, voles, and gophers are typically consumed.
How Barn Owls Nest
Owls in general do not build nests. In the case of barn owls, they historically nest in barns but have a wide range of nesting sites including towers, abandoned buildings, hollow trees, and banks. Basically, any fl at area that is protected is a possible nesting site.
Th e female places pellets around her to control the temperature of the nest and keep the eggs from rolling around. She breaks pellets and uses the fur of the prey to line the nest and keep the eggs in the center of the nest. Th e number of eggs is generally fi ve to eight, but the size of the clutch (nest of eggs) is determined by availability of prey in the area. Unlike the other species of owls in Oklahoma, barn owls will have multiple clutches of eggs if food is abundant throughout the year. Th e largest clutch of barn owl eggs that I have observed was 23 eggs. Th at pair of parent barn owls produced four clutches of eggs that year and successfully fl edged the young in all four clutches.
Th e incubation period for barn owl eggs is 30 to 34 days. Th e female starts incubation with the fi rst egg. Generally, a two-day span occurs between eggs, so if the clutch has 17 eggs, the fi rst egg would hatch with the arrival of the seventeenth egg.
Th e young are in the nest approximately 45 days before they fl edge, but they generally remain with the adults for a while to be fed and to learn how to hunt. If the young survive the fi rst year, they have a fair chance of living 10 to 20 years.
If the habitat is stable, the adult pair of barn owls might stay in their home territory year-round (mesquite and pastureland) or in areas that have several types of crops (wheat, corn, cotton, peanuts, soybeans, and milo, or maize) to support the prey species.
Barn owls still use the Type 2 houses that Owasso Science Club built almost 30 years ago and still produce young owls in them each year. In May 2024, the number of barn owl eggs was reduced in southwestern Oklahoma but was above normal in northwestern Oklahoma because of increased rainfall and prey population in that area. Th e houses help to maintain the population of barn owls in Oklahoma despite the loss of barn lofts fi lled with hay.
