connecting to nature

Barn Owl Report


Ramona Van Riper
Wildlife Rehabilitation and Management
Independent Study

The barn owl, Tyto alba pratincola, is the only member of its species found in North America. Though its distribution is wide, ranging from the Pacific to the Atlantic coasts and almost as far north as Canada, the barn owl’s numbers have been steadily decreasing in its northern range for several years.
Listed as an endangered species in 7 states, and a species of special concern in several others, the barn owl has very rigid habitat requirements. The species tends to be restricted to areas with a great deal of open space, hedges, and rough grass. This provides the optimum arrangement for gathering the owl’s main prey species; small mammals and rodents, especially voles (Read and Allsop 1994, p38).
Since the early 1800’s, barn owls have inhabited manmade structures throughout the countryside. Because of their close association with man, the species’ decline has been much more noticeable than that of less conspicuous species. In the mid 1950’s to 1960’s, the barn owl’s numbers began dropping drastically, due to widespread use of the pesticide DDT. The birds’ diet consisted almost entirely of small animals hunted from local agricultural fields, many of which had been affected by the chemical. Concentrated levels of poison began to build in the owls, affecting the strength of their eggshells and resulting in the failure of many broods (Taylor 1994, p239).
Loss of foraging habitat and loss of nest sites are among the other most significant causes of the barn owl’s population decline. With modern advances in agricultural technology, fields have been enlarged and manicured, to allow for machine access. This has reduced the rough edge-habitat that provides optimum foraging ground for the barn owl. (Taylor 1994, p235). Before the agricultural revolution of the 1950’s and 60’s, there were many traditional farmlands, with barns, sheds, and lofts ideal for the nesting and roosting of barn owls. The birds came to rely heavily on these structures, preferring them to less available natural cavities.
Today, many of these old buildings have deteriorated through age, or been torn down and replaced by large multipurpose open sheds. Such modern structures do not offer hospitable nesting or roosting sites, and the demand for heightened sanitation has led to conscious measures to impede the entrance of barn owls to agricultural storage facilities (Taylor 1994, p236). The barn owl’s population has become critically imperiled, to the point where the species is now dependent on positive human intervention to ensure its continuation.

Life Cycle
Barn owls begin breeding in early spring, usually around the beginning of April. They can raise up to three broods a year, each brood containing as many as nine eggs. Occasionally, several females will share a nesting box. In such cases, the owls will share the responsibilities of incubating a brood of up to 18 eggs (Taylor 1994, p149). Barn owl young have a very high mortality rate in the wild. They suffer from starvation, collision with fences and vehicles, and predation. It is estimated that 80 percent of all barn owl young do not successfully reach maturity (Read and Allsop 1994, p93). In recent years, this percentage has increased, due to the introduction of habitat-altering technology, and a growing number of highways. Even the prolific breeding rate of the species has not been able to compensate for their high losses.

Established in 1987, Hawk Creek Wildlife Center remained a small-scale rehabilitation facility for seven years. The organization focused mainly on the treatment of individual sick, injured, and orphaned animals. In 1994, Hawk Creek administrators began looking into the possibility of establishing a captive breeding program with non-releasable raptors. Through study and research, they determined that the barn owl would be a very favorable choice of a focus species. The barn owl is very beneficial to man, as its main prey species are small rodents that are often considered pests. The number of mice that a barn owl can kill in one evening is comparable to that of ten domestic cats. This bird was in a critical state of endangerment in Western New York at the time, but had developed a reputation for being a very successful captive breeder.

In 1867, a pair of captive barn owls in the British Isles were successfully paired and bred. This was the earliest documented captive-breeding program for the species (Terres 1996, p663). Since then, the barn owl has been successfully bred in captivity by various organizations. Barn owls lay several clutches a year, each containing many eggs, and have proved to adapt well to captive situations. For these reasons, the administrators at Hawk Creek decided to attempt the breeding of this species.
In January of 1994, a pair of barn owls was obtained from a rehabilitation center in Arizona. Both birds had permanent wing injuries, and could not be released. They were placed in a 12′ x 12′ x 10′ cage, and left in a private location for five months in order to bond to eachother and become comfortable with their new enclosure. The owls were fed mice, gerbils, hamsters, and rats, which were provided through a small door in the side of the cage, to minimize disturbance. The nesting box was situated in an upper corner of the cage, and equipped with a trap door and one-way glass for viewing purposes.
By May of 1995, the pair had laid a clutch of four eggs. Because the pair had never been bred before, there was uncertainty as to whether the eggs would be fertile. Studies have shown that barn owls may incubate infertile eggs for up to six weeks before abandoning the clutch (Taylor 1994, p154). The eggs did hatch in 30 days, however, and The Hawk Creek volunteers let the parents raise the chicks, monitoring the clutch daily

Considering that this was the first and only clutch produced in the parents’ initiatory year of breeding, it turned out to be highly successful. Two out of four eggs were hatched, weaned and released without incident. The second clutch, however, was laid on the top of the nesting box. The staff learned that barn owls are very unpredictable nesters. They are very discriminating in their choice of nesting and roosting sites, and prefer not to reuse a cavity, once it has been soiled by a previous brood (Read and Allsop 1994, p41). The male’s injury did not permit him to reach any higher than the nesting box already was, so it could not be raised. In subsequent seasons, the nesting box was dusted out between clutches, and the side door removed for ventilation in the warmer months.
The parents found it difficult to control a brood of six atop the nest box. There were no walls, and no way to contain the restless chicks. When the smallest of the chicks began to be pushed over the edge of the nest too many times, the Hawk Creek staff pulled him from the nest. They obtained a permit to keep the young owl, and hand-reared him for use as an educational ambassador for the project. He was housed with another non-releasable female from Arizona, but the two did not bond. They had to be provided with separate boxes, as the female would not allow the male in her box for the winter.
In the spring of the following year, however, the educational owl was found in the same box with his female companion. The pair was incubating a clutch of eggs. The caretakers allowed the pair to raise the brood, but were required to remove the male frequently for use in previously scheduled educational programs. The clutch was successful, and the two were designated as another breeding pair. They have since produced two to three clutches per year.
The first season of the barn owl breeding program at Hawk Creek Wildlife Rehabilitation Center proved to be a considerable learning experience. After a brood has matured enough to be weaned from their parents, the chicks are removed from the enclosure and the parents produce a new clutch of eggs very shortly after. One pair, however, produced their third clutch very late in the season, and as a result, the birds did not reach maturity until it was too late to release them into the wild. The owls had to remain at the center until spring, when weather and prey conditions would be suitable for release. In order to prevent this from reoccurring, the first two broods are removed from the enclosure before they are completely old enough to fend for themselves. Hawk Creek rehabilitators finish rearing these young, and the parent birds begin their third clutch early enough for the babies to be parent-raised and successfully released, that same season.
Winter of 1999 brought one of the heaviest snowfalls ever recorded in Western New York. Within two weeks, 68 inches of snow had accumulated around the breeding cages at Hawk Creek. At the time, two of the captive barn owl pairs were incubating eggs. Both pairs destroyed their clutch unexpectedly. This was the fist time any of the owls had exhibited such behavior: both pairs had raised several successful clutches in the past, without incident. The rehabilitators speculated that the owls’ actions were based on instinct. With the snowfall, the owls may have expected that there would be a shortage of food, even though they were being provided with their customary surplus.

Before being considered for release, an owl must have reached a level of capability that will allow it to survive in the wild. They must be capable of catching their own food, flying great distances, enduring the elements of the local climate, and dealing with predators and other dangers. If the birds were acclimated to humans as a source of food, or even as a natural figure in their local habitat, they would be highly vulnerable once released. It is important that they display defensive posture when approached, to ensure that they have not become comfortable with human presence.
As a preparation for the transition into the wild, the owls are placed in a 150-foot long flight cage outdoors. Here, the birds and decrease their contact and association with humans and receive the exercise necessary to condition their wings for long-distance flight. They learn to handle greater exposure to the elements, and begin to catch some of their own food. At each end of the cage there is an enclosed shelter, constructed similarly to a barn. The remaining 140 feet of the cage is constructed of synthetic mesh upheld by a telephone poles and wire cables.
Not only must the owls themselves be in a suitable condition for release: there are a number of evaluatory prerequisites for release site, as well. The staff at Hawk Creek follow a release-site scoring system created by the Iowa State Conservation Commission (see appendix 1) to determine the suitability of potential release sites for their captive-bred barn owls. According to this system, in order for a site to be considered for use, it must consist of a blend of dense grass pasture; hayfields; grassy roadside and ditches; fencerows, hedges, or windbreaks; and large timber. Individuals who are willing to feed the owls must be present, and a number of suitable undisturbed nesting cavities must be identified. The release site regarded with stronger consideration if established pairs of nesting barn owls have been identified in the locale. This confirms that the site has all the components necessary to support the species.
A potential release site’s score is decreased if it is found to contain a large number of corn, beans, or wheat fields. These grains grow very densely, and the structure of such fields does not provide optimum hunting habitat for the barn owl. Barn owls are unable to dart between the closely packed stalks to catch their prey. Scattered woodlots provide inconsistent habitat, and will also reduce site scores. The presence of great horned owls, one of the barn owl’s chief predators, also decreases the site’s suitability for barn owl habitat.
Release of a captive-bred animal must be a slow process, allowing the creature to enter its new environment gradually. “Hacking” is a commonly used method of release that allows young birds to enter their new environment progressively and in a natural manner, without excessive contact with or dependence on humans. In this process, young birds are placed in an outdoor enclosure when they are capable of maintaining their body temperature and feeding themselves without the aid of a parent. They remain in the enclosure until they are fully flighted, at about two and a half months of age. At this point, a door is opened that allows the birds to enter and exit as they please. The birds return and live in the hacking boxes for a period afterwards. During this time, food is supplied, to sustain the birds as they learn to hunt for food on their own. Eventually the bird leaves the hacking box, to establish a territory in the surrounding area. (Beebe and Webster 1985, p138) The process is very similar to the manner in which an owlet would be weaned from its parents’ nest.
The rehabilitators at Hawk Creek chose a structure on the property to be designated for this purpose. The enclosed “hacking tower” was equipped with roosting boxes, and the first captive-raised brood was moved in as soon as they had begun to self-feed. Food was provided to the tower residents with minimal human contact, and they remained in the tower until they were between four and five months old.
When the owls were ready for release, a door at the top of the structure was opened, and they were given the ability to leave the tower. For a few days, the birds returned for the food that the rehabilitators continued to supply. Within four days, however, they had adapted to hunting in the wild, and did not return. The owls were seen in the neighborhood for about four weeks before they dispersed to establish new territories.
Studies of northern barn owls have revealed that, after fledging, the young travel great distances before settling into new territories. Barn owls have been documented as traveling as many as 200 miles from their hatching place, and dispersal usually ranges between 50 and 150 miles (Taylor 1994, p195). Once settled, the barn owl rarely moves from its adult territory (Taylor 1994, p96). In The Barn Owl, Read and Allsop (1994, p40) relate records of barn owls nesting as closely as 23 pairs in a 50 kilometer plot, just over 2.17 square kilometers per pair. In nearby areas, there were as few as 11 pairs per 100 square kilometers (9.1 square kilometers per pair.) The book states that “population density varies enormously depending on the availability of food and nest sites.”
Since their first successful endeavor, the rehabilitators at Hawk Creek have expanded on the hacking-tower release method. Once the captive breeding program began gaining publicity and popularity among the locals, they approached the possibility of using local barns as release sites for their captive-bred owls. The community took well to the idea. The barns were closed up securely, and the owls were introduced into the enclosed habitat. Rehabilitators brought small amounts of food each day, and but it became less necessary as the owls adapted to hunting among the hay and straw of the dark barn.
After several weeks, the barn is opened, and the birds begin leaving and returning at will. This method allows the owls to integrate themselves into the habitat gradually, as does the hacking tower. However, with the use of barns, the birds are provided with a permanent protective structure that can be adopted as a home base, and possibly used for future nesting. They are not forced to immediately move on to a new territory and adapt to a new habitat, as they must do when released from the hacking tower, which is reused many times in a season.
Public response to the program has proved very enthusiastic. Hawk Creek has put a great deal of effort into educating the public about the benefits of the barn owl as a rodent regulator, and local farming communities have welcomed the creature onto their land and into their barns.

Each barn owl that is bred at Hawk Creek is banded upon release. Within two years of the first successful release, three non-banded barn owl chicks were brought to the center, in need of rehabilitation. These young owls were the first recorded barn owl patients in Western New York in over 25 years, and they proved that the wild barn owl is breeding in the region once more. The rehabilitators put the chicks in a nest with one of the resident breeding pairs. They were successfully raised and released in good health.
In December of 1998, one of Hawk Creek’s banded owls was brought in for rehabilitation after being hit by a car. The owl had traveled over 400 miles in two months. This incident indicated that the repopulation effort was having an effect on more than a local scale. Over the past five years, Hawk Creek has bred and released 70 barn owls. Barn owl sightings have become more common, and the species has begun to show up at wildlife rehabilitation centers throughout the region. What is now the rarest raptor in Western New York may soon become abundant once more.

References and Works Cited

Beebe F and Webster H. 1985. North American Falconry. Denver: Jostens Printing and Publishing Division. 386 p.

Ehresman B, Reeves D, Schlarbaum, K. 1989. Post Release Survival and Movements of Captively Reared Common Barn Owls in Iowa. Boone IA: Iowa Department of Natural Resources; Wildlife Research Station.

Jones, L. “Breeding the Flying Mousetrap-Barn Owls”

Read, M and Allsop, J. 1994. The Barn Owl. New York: Sterling Publishing Co, Inc. 128 p.

Taylor, I. 1994. Barn Owls: Predator-Prey Relationships and Conservation. New York: Cambridge University Press. 304p.

Terres, J. 1996. The Audobon Society Encyclopedia of North American Birds. New York: Wings Books. 1109 p.

Intradepartmental Communication: State Conservation Commission-Des Moines, Iowa. 29 August 1983. From Dave Newhouse, Living Records, to Dean Roosa, Ecologist. Subject: Captive Breeding Synopsis.

Appendix 1

Barn Owl Release Site Scoring Formula
Developed by the Iowa State Conservation Commission




Sum =________

Total =________

Appendix 2

Barn Owl Nest Box Locations: Erie & Niagara Counties, New York
April 25, 1998