Among Missouri's owls, barn owls are champion listeners, able to detect the location of a mouse using only their ears. They are oddities among Missouri owls in other ways. Barn owls are the only light-colored owls that nest in Missouri; barn owls have golden backs and white bellies. Their plumage is sparsely speckled with small black dots. Their heart-shaped face is white and outlined with tan.
Barn owl eyes are small and dark, differing from the large, yellow eyes of most owls. A long bill and long legs, feathered to the toes, give barn owls an ungainly appearance. They have a strange habit of bobbing their heads and shuffling from side to side when discovered.
While other owls hoot, barn owls emit loud, spine-chilling hisses. Children exploring dim barn lofts or seeing this light-colored owl silently glide by could easily mistake these owls for ghosts. In fact, they are sometimes called the ghost owl.
Barn owls are medium-size owls, reaching 14 to 20 inches in length and weighing about one pound. However, they have unusually long wings, with wingspans of 43 to 47 inches. As is the case with most raptors (birds of prey), female owls are larger than males.
Enjoying a nearly global distribution, barn owls inhabit open landscapes, ranging from desert to marsh, on every continent except Antarctica. Barn owls are year-round residents in Missouri and have been found in open areas throughout Missouri, except in the Ozarks. They are most abundant in the Bootheel and in the Osage Plains of southwestern Missouri.
Reputed to be excellent mousers, barn owls consume twice as much prey for their weight as other owls. Small mammals, including mice, moles, shrews, cotton rats, Norway rats, gophers and rabbits, form the bulk of the barn owl menu. Voles, small rodents with short tails, are the primary food when available. Barn owls occasionally feed on birds, insects, reptiles and amphibians.
During breeding season, male barn owls hiss in flight to attract females and to warn away other males. Barn owls form monogamous, long-lasting pair bonds. They can nest any time of the year and can produce two to three broods per year when food is abundant. However, most pairs nest from March through July.
Natural barn owl nest sites include tree cavities, burrows and crevices in rock outcrops and cliffs. As large, hollow trees disappeared and settlers built barns with open lofts, barn owls quickly adopted barns and other buildings as nesting sites. Today, they are most commonly found in out-of-the-way corners of barns, silos, grain bins and attics.
Barn owls do not construct nests; they simply lay their eggs in a small depression scraped in loose substrate. If loose material is not present, eggs will roll away from each other and fail to hatch.
Barn owls may lay up to 11 eggs, although the normal clutch size is four to seven eggs. The female begins incubation when the first egg is laid, unlike most other birds, which delay incubation until the last egg is laid to cause simultaneous hatching. Barn owls lay subsequent eggs every two or three days.
Eggs hatch after 21 to 24 days of incubation. However, because the last egg may be laid a week after incubation began, the female may have to incubate for 32 to 34 days before all eggs are hatched. For comparison, chickens incubate their eggs for 21 days and turkeys for 28 days. Males bring food to incubating females.
This incubation strategy results in siblings occuring in stair-step ages. The first owlet may be 6 to 18 days older than its youngest nest mate. This age difference is visible in the varying size and plumage development of nestlings. Young owlets may still be covered head-to-toe with a short, white down when the oldest nestling, with plumage resembling that of an adult, is ready to fledge. Young owls fledge when they are about eight weeks old.
Parent owls keep busy feeding themselves and their hungry owlets. Each adult consumes the equivalent of a large rat every night. Each owlet would eat up to a dozen mice per night if given the opportunity.
With a normal nest containing six young, parent birds must capture up to 74 rodents nightly. To capture such a supply of food, adult owls may travel three miles. If they do not catch enough to eat at night, barn owls will hunt during daylight.
Bones, fur and other indigestible parts of prey are compacted into pellets (oblong, dark objects about 2 inches in length) and regurgitated. Biologists examine the skulls in the pellets to identify the kinds of animals owls are eating. The enormous quantity of pellets littering a nest area testifies to the amazing number of rodents a family of barn owls consumes. The presence of pellets is one of the first clues that barn owls are using a building.
The staggered ages of barn owl nestlings increase the odds that at least one young will survive to adulthood. If the supply of small rodents is plentiful, all of the young owls may survive to fledging. However, if the parents are unable to find enough food for all of the youngsters, younger nestlings cannot compete with older, stronger siblings for food and will die. Weakened or dead young may even be cannibalized by siblings.
Unless the rodent population completely crashes or a predator discovers the nest, at least one of the owlets is likely to survive. However, if rodent populations are low, barn owls may skip a breeding season.
Although barn owls are birds of prey, they still fall prey to other predators. Raccoons, black rat snakes, house cats and other nest predators readily consume barn owl eggs and young. Great horned owls are probably the most common predator of adult barn owls.
Lifespans of barn owls are rather short, believed to be 5 to 11 years in the wild. To compensate for this short lifespan, barn owls rely on their unique reproductive potential to perpetuate the species.
Researchers have found that barn owls are capable of catching prey using only their hearing to direct their attack. They placed owls in completely dark rooms and used sophisticated equipment to broadcast the minute sounds of a mouse going through its nightly business from different locations in the room.
With amazing accuracy, the owls repeatedly struck the exact locations from which the sounds were emitted. Not only were the owls able to locate the sources of the sounds, they were able to calculate the direction and speed of movement to strike a moving target.
This type of ability requires specialized hearing equipment. The large, heart-shaped face of barn owls serves as the equivalent of the outer ears of mammals. Short feathers on the face and side of the head form a groove that funnels sound waves into the ear openings.
A moveable flap of skin at the front of the ear opening may be raised to assist in catching sound coming from behind. This flap also may be closed to protect the sensitive inner ear parts. The right and left ear openings are shaped differently and occur at different heights on the sides of the head.
This lopsided arrangement allows owls to receive the sound from slightly different perspectives and helps them pinpoint the origin of sounds. The inner ear parts of owls also relay sound stimuli up to 10 times faster than human ears.
Barn owls not only are oddities among the bird world but also are unusual finds in Missouri. Listed as state endangered, barn owls have declined with the loss of open grasslands and nesting sites. Because their survival and reproduction is closely linked with their food supply, declines in rodent populations also seriously impact barn owls. Pesticides, passed along and concentrated in the food chain, harm barn owls by causing thin eggshells and reducing prey populations.
Because of the rarity of this species, the Conservation Department tracks barn owl nest locations to monitor population trends. The Conservation Department also works cooperatively with landowners to protect and encourage nesting pairs. Landowners with barn owls nearby receive bonus points when applying for CRP and other Farm Bill assistance programs.
Because barn owls readily use human-made structures for nesting, landowners can do something to help this beneficial, unique inhabitant of Missouri. Landowners who find barn owls on their property or wish to attract them can install nest boxes. Barn owls will nest in a simple box placed in a barn loft or other suitable man-made structure. One or two inches of wood shavings or hay provide a cushion for the eggs and young owls.
Once a pair of barn owls selects the nest box, they often will use the structure yearly. Nesting boxes installed in a building already being used by barn owls will help contain the litter of pellets and provide a safer place for raising young.
People who have barn owls nesting nearby are fortunate to have the opportunity of watching these champion hunters raise their families. They may see the young birds line up to be fed and eventually fly and begin to hunt for the first time. They also reap the benefits of having one of the most efficient mousetraps available.