The Barn Owl
Originally published in the September/October 1992 edition of the S.D. Conservation Digest.
by Eileen Dowd Stukel
Photo by Doug Backlund
Owls have a strange and unusual place in human history. Just consider the many superstitions surrounding them. The Scottish thought it bad luck to see an owl during the day. The Romans took this belief one step further. An owl seen during daylight hours was caught, burned and its ashes scattered in the Tiber River. A common superstition is that a hooting owl signals an impending death. The haunting calls and nocturnal habits of nearly all owl species gave rise to an association with evil and witchcraft.
But what about other owl folklore? An owl's wide-eyed and sedate demeanor gives the impression of wisdom and maturity, as expressed in the following poem:
A wise old owl sat in an oak,
the more he saw the less he spoke,
the less he spoke the more he heard,
why can't we all be like that wise old bird? Anon.
An Australian tribe protected all owls, believing that each woman's soul had an owl as its guardian. An old English remedy for poor eyesight required the sufferer to eat charred, powdered owl eggs.
Owls are indeed a remarkable group, not because of any supernatural powers or abilities, but because they are uniquely suited for their role as nature's nighttime predators. They share many characteristics with their daytime raptor counterparts, such as hawks, eagles and falcons. Similar body parts are the hooked bill and the long, sharp claws, or talons. The female is usually as large or larger than the male. Owls are typically monogamous, and begin incubation with the first egg laid. The method of killing prey is both consistent and efficient. The victim is first grasped and immobilized with the strong talons, followed by the severing of the neck vertebra.
But owls differ from other raptors in several ways. Most owls are nocturnal, few owls eat birds, none typically eats carrion, or dead flesh, and owls lack a crop, which serves as a storage chamber in many birds, especially grain-eaters.
Among an owl's most important attributes for its silent nighttime lifestyle are its eyes, ears and feathers. Owls have large, immobile, forward-facing eyes. This position allows better binocular vision and hence better depth perception. Owls have a relatively narrow field of vision, seeing 110 degrees, as compared to our 180-degree field. The eerie ability of an owl to rotate its head compensates for its narrow field of view. The retina is a membrane at the rear of the eye that receives an image. It contains a combination of cells, among them rods and cones. Rods are sensitive to poor light. As you might expect, rods are more common than cones in creatures with acute night vision. Cones are the more common retinal cell type in a daytime or diurnal vertebrate, which relies more heavily on distinguishing color and discerning detail.
As if excellent vision weren't enough, owls have acute hearing as well. Owls have ear openings on the sides of the head, as one would expect. The "ears" of the long-eared and short-eared owls are feather tufts without any known auditory role. Long vertical ear slits with asymmetrical ear openings allow an owl to detect and pinpoint sounds, many of which are the high-pitched sounds of its rodent prey. An owl's "face" is called a facial disc, which serves the useful function of gathering sound.
In deadly combination with an owl's vision and hearing is its silent approach, made possible by soft, fringed feathers and a low wing-loading ratio. Owls are relatively lightweight in relation to their wing area, which translates to flights with less flapping and more gliding. The lack of noisy wing-flapping helps an owl hear its prey, as well as be undetected by it.
A fascinating embodiment of the definition of an owl is the barn owl, previously known as the common barn-owl. This raptor belies its former name in being uncommon, and in fact rare in many areas.
The barn owl has a nearly worldwide distribution, with various geographical races found in all but the polar regions. A bird of temperate climates, its North American range includes virtually none of Canada, and it is rare or absent in the north-central United States. Barn owls are generally sedentary creatures and may continue using their nest site as a winter roost. However, barn owls that nest in the northern part of their range may migrate to milder climates for the winter.
All owls are members of the Order Strigiformes. Barn owls are distinctive enough to be separated from typical owls (Family Strigidae) into their own family (Tytonidae), where they are placed with the bay owls of Asia. An obvious distinction is the barn owl's heart-shaped face, contrasted with a typical owl's round or oval-shaped face. Less obvious are toe length and other skeletal differences. Barn owls are unique among Strigiforms in having a comb-like middle claw, presumably for grooming.
The barn owl, sometimes called the ghost owl or monkey-faced owl, measures 16-18 inches in length and has a wingspan of nearly four feet. It is distinguished by its white, heart-shaped facial disc, dark eyes, long and slender legs and white undersides. It is very nocturnal in habit, but may be seen when surprised at its daytime roost or nest site. The barn owl does not hoot, but instead utters a variety of sounds and calls that are territorial or defensive in function. It may screech, purr or scream when advertising its territorial rights. Defensive sounds include hissing, bill-snapping and tongue-clicking. Food-begging sounds have been described as snoring and chittering.
Characteristic barn owl habitat is low-lying, open country where grasslands are interspersed with such habitats as woodlands, pasture and meadows. In such a mixture, this owl may follow a regular hunting route, flying low in search of its favorite prey, typically small rodents such as voles, mice and shrews.
Prey abundance invariably determines predator numbers, rather than vice versa. The barn owl's reproductive strategy is a textbook demonstration. The male barn owl not only defends a pair's territory, but also feeds his mate at the nest as she lays a typical clutch of 4-7 eggs. The barn owl is not one of the bird world's elaborate nest-builders. It uses whatever material is nearby to roughly line the nest. Eggs are laid every 2-3 days, but, as is true for all owls, the female barn owl begins incubation after the first egg is laid. Such a habit results in a brood of owlets of differing ages and therefore differing sizes. In times of feast, or abundant prey, all chicks large and small may be fledged. In times of famine, when few rodents are caught by the adults, only the largest and strongest chicks will survive to fledge, usually at about eight weeks of age. In years of very low prey abundance, a pair of barn owls may not even attempt to nest. After fledging, barn owls in milder climates may begin courtship again, producing a second batch of young.
The barn owl's name is a clear indication that it has long been associated with man's activities. Barn owls don't, of course, always nest in barns. Natural nest sites might be found in hollow trees, cliff crevices, cavities in river- or streambanks, or old nests of other birds. The barn owl will not typically excavate its own nest cavity, but it has been known to dig a nest hole in soft substrate, such as in the Sand Hills of South Dakota and Nebraska.
Barn owls take advantage of nesting opportunities in manmade sites, such as barns, silos, towers and old buildings. This bird has profited from nest site opportunities provided by settlement, and has benefitted as well from changing agricultural practices. As forests were cleared to accommodate small farming operations, the habitat mixture favored by barn owl prey became available. "Sloppy" farming also enhanced rodent populations by providing or allowing weedy field borders and fencerows, natural hedgerows and spilled grain around the farmyard.
There are few better examples of a mutually beneficial relationship between man and wildlife than that of the farmer and the barn owl. A farm's resident barn owl pair may catch as many as 1,000 rodents during the nesting season, in exchange for a nest site in an old barn or building. European farmers encourage barn owls by providing special owl doors to assure that they can enter a barn.
The barn owl appears to have many competitive advantages as a wildlife species. It may live ten years or more, it can potentially produce many young in a nesting season and it has demonstrated a fair amount of tolerance for people and their activities. Why then is it a "species of special concern", according to the National Audubon Society? In at least ten Midwestern states, the barn owl is either officially listed as endangered or is considered rare or vulnerable by state conservation agencies. In South Dakota, known barn owl nest sites are scattered and few in number. Although documented from as far west as Fall River County, most nests have been found in natural cavities in banks of the Missouri River's reservoirs and adjacent drainages. Not much is known about the true distribution or abundance of South Dakota's nesting barn owls.
The reasons for the barn owl's decline are many, some proven and others hypothetical. The changing times that brought abundant prey and nesting opportunities for the barn owl didn't stop changing. Clean farming produced better crop yields, but at the expense of species dependent on hedgerows, weedy field borders, wet meadows and the other diverse habitats that were reduced or eliminated. Grasslands, where rodents abound, were converted for other uses. Increasing great horned owl populations are also considered a factor in barn owl declines. Pesticides are a suspected cause, but the degree of blame is unclear.
The barn owl serves as an indicator of the vigor of the grassland ecosystem. This species is not alone in suffering from grassland conversion and abuse. A number of recovery strategies have been tried to bring the barn owl back. Taking advantage of their considerable reproductive potential, captive breeding and subsequent reintroduction by hacking have been tried in several states, with mediocre results. At least two states, Ohio and Indiana, have tried a "sentinel box" recovery program for barn owls, where nestboxes are erected in grassland areas that provide potential rodent habitat. While other recovery methods will undoubtedly continue to be tried, the prevailing opinion among most raptor experts is that the most promising conservation strategy for barn owls is to enhance populations where they already exist and hope for natural expansion. On behalf of this beautiful and beneficial member of our Dakota heritage, we are asking for your help. How can you help the barn owl?
1. If you come upon a barn owl nesting pair, don't disturb them. Like most birds, they are very sensitive to disturbance and will readily abandon a nest, especially during egg-laying and incubation.
2. Report summer barn owl sightings, particularly of nesting birds to: South Dakota Natural Heritage Program.
3. If you think your farm has the potential to support barn owls but may lack nesting sites, build and erect a barn owl nestbox. Be sure to keep the Natural Heritage Program informed if you successfully attract a pair of barn owls.
4. If you're lucky enough to attract a barn owl pair to your barn or silo nestbox, consider yourself a benefactor of a creature that is truly one of man's best friends.