Posts Tagged ‘Endangered species’

Published in Proceedings at the National Wildlife Rehabilitation Symposium—1984.

Common Barn-Owl Restoration in Iowa

By  Bruce L. Ehresman

Common Barn-Owl Restoration in Iowa

Bruce L. Ehresman

Iowa Conservation Commission, Wildlife Research Station

Boone, IA  50036

Abstract:  One goal of the Iowa Conservation Commission’s Nongame Program is to increase the population of the Common Barn-owl, an Iowa endangered species. Reasons for restoration include its economic value as a destroyer of grain-eating rodents, its aesthetic value to humans, and publicity for the Nongame Program.

The Iowa Conservation Commission acquires barn-owls used for restoration from other rehabilitation centers and zoos in coastal states where the owls are abundant. We use these owls either for captive breeding at the Wildlife Research Station near Boone, or for placement at selected release sites, primarily in southern Iowa. We choose release sites from areas volunteered by the public, using evaluation criteria we developed. At each release site, commission personnel enclose a section of a building to contain the owls for gentle release. Barn-owl nest box construction in release site areas is promoted. Nearly 40 boxes were erected in 1983. We place barn-owls as mated pairs, pairs with young, or groups of immature.

In 1983, we banded and released 12 adult and 46 immature barn-owls using gentle release methods. Media coverage of restoration efforts has resulted in strong public support, evidenced by Iowa’s income tax refund Checkoff participation.

Barn-owls released in 1983, and future releases, will augment Iowa’s remaining breeding population, and nest boxes erected will re-create needed nest sites.

The Common Barn-owl, as most birds of prey, has been persecuted since it first came into contact with humans. It has been the victim of random and injudicious shooting, trapping, and poisoning. Most tragically, its habitat, including critical nesting sites, has been destroyed because of human ignorance in the pursuit to “improve” our way of life on this planet. The Iowa Conservation Commission (ICC) has embarked on a restoration program to change this unjustified public attitude and to increase the population of the Common Barn-owl, an Iowa Endangered species (Roosa 1977).

DISTRIBUTION

The Barn-owl family, Tytonidae, has a worldwide distribution. It consists of eleven living species and approximately 35 subspecies. Only one of these subspecies, Tyto alba pratincola, is found throughout North America. Populations in the United States are chiefly coastal, decreasing northwards. The Barn-owl is considered a rare, permanent resident of Iowa. Because it is intolerant of cold climates (Bunn et al. 1982), it rarely breeds in the northern part of the state. Most recent sightings indicate it is most numerous in the grassland areas of the south and west portions of the state.

ECONOMIC VALUE

Before European settlers arrived, Barn-owls nested primarily in the hollow cavities of old sycamores and cottonwoods. With the cutting of these cavity trees, the Barn-owl adapted to the use of man-made structures for nesting. It also switched from eating mice and voles of native grasslands, to feed on the rats and mice that were attracted to stored grain on farmsteads. According to Lewis Walker (1974), a Barn-owl authority, single owls saves the State of California between $20 and $50 annually in its predation on pocket gophers, where pocket gophers and ground squirrels cause an estimated crop loss of 10% each year. Add to this its services in destroying voles and mice (its preferred prey), and these owls certainly do have a positive economic impact.

STATUS

It is unfortunate that a species so beneficial to humans is becoming so rare in the Midwest. Presently, the Barn-owl is listed as Endangered not only in Iowa, but also in Missouri (Wadell and Crawford 1982), Illinois (Becker 1978), and Wisconsin (Petersen 1979), and is considered threatened in Michigan (Taylor 1978).

LIMITING FACTORS

Decline of the Barn-owl can probably be attributed to a combination of factors, some interrelated. Loss of habitat, especially loss of nest sites, may be an especially important factor. Farmers have bulldozed vacant farm buildings and old hollow trees that once provided nest and roost sites, to prepare more land on which to grow cash grain crops. Modern clean-farming practices and the elimination of hay and pasture ground, prevalent on farms as recently as the mid 1960’s, has reduced habitat of the Barn-owl’s small-mammal prey.

Pesticide and rodenticide use undoubtedly have negative effects on the predator Barn-owl. Use of pesticides, particularly the chlorinated hydrocarbons, was probably most detrimental to Barn-owl populations 15 to 20 years ago before stringent regulations banned, or at least regulated their use (Bunn et al. 1982).

In Iowa, there are at least two predators that exploit the Barn-owl. Raccoons inhabiting old farm buildings harass and predate nesting Barn-owls. In the past few decades, raccoon numbers have increased in Iowa (Andrews et al. 1982) and adjoining states such as Wisconsin (Petersen 1979b). Competition with and predation by Great Horned Owls may also be a limiting factor (Wayne 1924).

Certainly collisions with automobiles, trains, power lines, etc., take a toll on Iowa’s Barn-owl population. From 1981 to 1983, 4 of 6 reported Barn-owl mortalities in Iowa were attributed to collisions.

Severe winter weather also affects survival of Barn-owls. Stewart (1952) indicated Barn-owl survival in its northern range was more influenced by snow cover amount than low temperatures. Petersen (1979a) found that snow cover depth of 10 cm or more provided cover for small mammals and protected them from owl predation in southern Wisconsin, which corresponds in latitude to northern  Iowa. Since the Barn-owl maintains the lowest body fat reserves (5.5%) of all owls examined by Piechocki (1960), it seems likely the Barn-owl cannot survive more than 3 to 4 days without feeding (Stewart 1952), especially during periods of sub-zero temperatures. Two of 4 wild Barn-owl mortalities reported in Iowa in 1983 were attributed to starvation during severe winter weather.

RESTORATION

1. States of Development

Since Iowa’s Barn-owl has been decreasing for several decades, and since the Barn-owl breeds readily in captivity, recommendations were made by Iowa’s State Ecologist, Dean Roosa (1977), to embark on a captive breeding and restoration program. Common Barn-owl restoration in Iowa began as an offshoot of the ICC’s raptor rehabilitation project at the Wildlife Research Station (WRS) near Boone. From 1960 top 1980, the facilities were used to hold birds and mammals for the state Wildlife Exhibit. Funding provided by hunting and fishing license fees allowed a wildlife rehabilitation project to begin in the late 1970’s, when Iowa’s first nongame biologist was hired. A reduction in State expenditures forced the closure of the Wildlife Exhibit in 1980.

Raptor rehabilitation at the WRS still continues, but since the fall of 1982, our main emphasis is on captive breeding, rehabilitation, and restoration of the Common Barn-owl. Reasons for restoration include its economic value as a destroyer of grain-eating rodents, its aesthetic value to humans, and publicity for the Nongame Program. Funding is now derived from an Iowa income tax refund Checkoff initiated in tax-year 1982 for Iowa’s Nongame Program.

B.    Source

Since it was virtually impossible to locate native Barn-owls for captive breeding, we had to look to outside sources. We contacted successful breeders mentioned in International Zoo Yearbooks, and publicized our project in several veterinary journals and magazines. Response was good. So far, we have received Barn-owls by air-freight shipment from rehabilitation centers in zoos in Washington, Oregon, California, Louisiana, and South Carolina. We paid air-freight costs, and during 1982-83 we received 71 Barn-owls at an average cost of about $13 per owl. We use these owls either for captive breeding at WRS facilities or for placement at selected release sites.

C.    Housing

Housing facilities at the WRS include a 14’x80’ wooden building divided into 8, 10’x7’8’ (LWH) and 4, 10’x4’x8’ pens, and a 40’x60’ steel shed containing 8, 8’x7’x8’ breeding pens connected to exterior 20’x8’x8’ flight chambers. Pens are wood framed, with walls of corrugated fiberglass panels and olefin netting. Most pens are visually separated by solid partitions to allow breeding Barn-owl pairs privacy. We place nest boxes in each pen, as well as various diameter tree branch perches. Metal flashing or smooth fiberglass skirting, two feet height, placed around the perimeter of each pen retains live mice for the owls to prey upon. Small pea gravel covers floors to facilitate cleaning. We clean pens about every three weeks, except when hens need minimum disturbance during nesting.

D.    Feeding

The diet and health of captive Barn-owls requires continuous attention. We feed routinely six days a week and fast one. Food is placed on wooden pallets, and uneaten food is removed daily. During winter months, heated food trays, modeled after those of Katherine McKeever (1979), keep the owls’ meals from freezing. We disinfect feeding pallets periodically to ensure harmful microorganisms are not transmitted to or between the owls.

Diet consists of a prepared Birds of Prey diet[1], day-old cockerel chicks culled from a local hatchery, and laboratory mice acquired from the National Animal Disease Center and Iowa State Diagnostic Laboratory in Ames. We feed these three different food items on a rotational basis to assure a balanced diet for the owls. Day-old chicks, deficient in calcium, are powdered with bonemeal before begin fed, and other supplemental minerals and vitamins are added to the diet when necessary.

E.    Medical

We treat sick or injured birds according to recommendations made at the Iowa State University’s College of Veterinary Medicine in Ames. They provide treatment and diagnoses at a teaching discount, since we provide some hands-on experience with wildlife species for students training at the clinic. We also isolate new birds brought into the facility to prevent the introduction of pathogenic organisms to or from other birds. Our personnel keep records on each owl’s health and history.

F.     Captive breeding

The ICC hopes to increase wild Barn-owl populations by releasing breeding pairs with young, and fledglings from other rehabilitators, as well as from our captive breeding pairs. All owls received from other sources are at least temporarily held at WRS facilities. Permanent cripples, human imprints, and owls that have been held several years in captivity comprise most of our captive breeders. We pair the owls for breeding according to size, temperament, age, and body condition; and place them together using methods suggested by McKeever (1979). Owls of similar sizes and temperament are our most successful breeders.

G.    Release site suitability

Before Barn-owls can be placed, release sites must be selected. We choose release sites primarily from areas volunteered by the public. After reading about this project in the newspaper, cooperators, who feel they have adequate hack sites and are willing to feed captive Barn-owls, notify Iowa’s nongame biologist. We send volunteers a “Barn-owl Release Site Preliminary Evaluation” form to complete and return. They complete this form with an aerial photograph of the proposed site, obtained from their local ASCS office. We evaluate and rate each returned form and choose release sites from those forms indicating the best habitat for Barn-owls.

Evaluation of the proposed release site includes the area within a one-mile radius of the release site structure (roughly 2,000 acres), based on the owls’ hunting behavior. The release site structure must be undisturbed, and able to be made “owl tight” with a few hours’ work. Criteria for choosing a release site are as follows:

Positive aspects –

(1)   Abundant grassland (pasture, hayfields, waterways, roadsides)

(2)   Timber in large, continuous tracts (if present)

(3)   Several people willing to feed and care for owls

(4)   Other undisturbed nest sites available nearby

Negative aspects –

(1)   Large amounts of cash grain crops

(2)   Resident Great Horned Owls present

(3)   Nearby use of rodenticides

Basically, we are looking for areas with a large proportion of permanent grassland, which have several undisturbed potential nesting sites (Bunn et. Al. 1982), and few Great Horned Owls present. Dense grasses provide good habitat for small mammals which the Barn-owl prefers as prey. Old vacant buildings or large hollow trees provide adequate nest sites. Since Great Horned Owls have been known to prey upon Barn-owls, we prefer to release our owls where such predators are not numerous. Most release sites are in areas where Barn-owls are present, or were present, within the last 5 to 20 years.

H.    Release site preparation

Once a release site with a suitable confinement structure is selected, the site must be prepared for the owls. Ideally, we prefer to allow confined owls an entire building or silo in which to fly about. This is not always possible. Usually, we are at least able to allow the owls the freedom of an entire barn loft. We close all exits, using boards or olefin netting. We then line a 16-inch square nest box, with a six-inch diameter entrance hole, with two inches of wood chips, since Barn-owls are not known to construct nests. Next, we attach this box near the top of each structure in a place that is as nearly predator-proof as possible. In silos, we place the nest box approximately two-thirds of the height above the floor (Marti et al. 1979). We supply large stock tanks to the enclosures containing fledgling owls. Live mice released into these tanks allow young Barn-owls the opportunity to learn to catch their prey before release to the wild.

I.     Placement

Barn-owls released in 1983 were placed as mated pairs, pairs with young, and groups of immature. We supplied cooperators with meat to feed the owls, and they fed the confined owls daily and monitored food consumption. Cooperators continued to feed the owls after their release until the birds were self-sufficient.

In 1983, we place 4 mated pairs (normally second-year owls) at release sites, prior to the main breeding season. In our captive Barn-owls, this has been from January through March. The hen from one pair appeared to be nesting in hay on the barn floor when she was not seen for several weeks. Since the paid did not nest successfully, and because cooperators could not fee the owls through the winter months, the pair was captured and returned to the WRS facilities prior to winter. A second pair remained captive for almost an entire year and just recently began courtship. Two captive pairs did nest after 2 months and 5 months, respectively, and fledged 5 young each. We released one of these pairs with young, but held captive the second pair with young over winter. Since these young fledged in late fall, we felt gentle release in early spring, rather than winter, would increase their survival chances. Normally, when the owlets fledge and catch live mice proficiently from the stock tank, it is time for gentle release. We open the structure so the occupants can hunt natural prey in the area near the release site. By allowing the owls to raise young at a site, we hope a bond will be established, so that either the nesting pair or their young will return to nest again in the future.

A second method of placement, which we feel is successful, is placing pairs with young. This method works well at sites where cooperators do not wish to feed captive owls daily for more than 2 or 3 months. During 1983, 5 Barn-owl pairs were placed with their 176, 3- to 4-week old young, which they hatched at the WRS.

Originally, we intended to allow parent owls freedom to hunt for natural prey outside the structure when the young are about one month old. Theoretically, the presence of the young will draw the adults back to the barn. Jane Ratcliffe (1979, cited by Bunn et al. 1982) of England, experienced good success using this method with Barn-owls. Unfortunately, the first time we tried this strategy, both adults vacated and did not return to feed their young. Our cooperator was then faced with the problem of feeding 5 very hungry owlets. It should be mentioned that we tried this method with a pair of Barn-owls and young that we moved to the site only several weeks before. With the remaining pairs, we used the same release techniques described for mated pairs – waiting until the young fledged before allowing freedom for the entire family unit. In 4 cases, this included foster young.

When the owlets of 4 family units were 6 to 8 weeks old, we added 8 more young of the same age to the broods, 2 owlets to each foster family. Four of these were WRS hatchlings, and 4 were from California. We experienced no problems with fostering young, as long as all young involved were nearly the same age.

Besides the Barn-owl family units, immature Barn-owls were also gently released. We held these owls captive at the release site for only 4 to 5 weeks. They were WRS fledglings and young owls received from California and Louisiana. To discourage inbreeding, we placed Barn-owls of different parentage at release sites of close proximity (40 miles). Volunteers hacked 4 immature owls at each of 4 sites.

In 1983, a total of 12 adult and 46 immature Common Barn-owls were banded with lock-on U.S. Fisheries and Wildlife Service leg bands and gently released. We hope this number of released owls is significant enough to have beneficial effects on the future Iowa wild breeding population. Our goals will be met when we know of at least 5 self-sustaining Barn-owl populations in Iowa habitats.

J.     Follow-up

We feel it is important to monitor the Barn-owls, even after release. Post-release monitoring is presently conducted primarily by volunteer cooperators. We ask these cooperators to keep records of post-release activity, including feeding and artificial nest box use. To ensure released owls of other roost and nest sites, at least one other nest box is erected in a vacant or little-used structure within a one-mile radius of the release site. As many as 10 nest boxes have been constructed and put up by concerned citizens in any one release site area. During 1983, nearly 40 nest boxes were erected in release site vicinities. Because our Nongame staff lacks time and manpower to monitor every nest box placed, we do appreciate the release site cooperators, County Conservation Board members, and other ICC personnel who voluntarily monitor nest box use.

Since loss of suitable nest sites is a factor in the decline of the Common Barn-owl, the ICC is promoting the use of artificial nest structures to increase our wild population. In Utah, 30 nest boxes were used by 24 barn-owl pairs to produce 154 young in 2 years (Marti et ala. 1979). We make available to the public Barn-owl life history brochures which include nest box construction and erection instructions. Many citizens have already used these instructions to build and place nest boxes.

K.    Media coverage

Media coverage at Barn-owl placement sites and about the Barn-owl restoration program has been instrumental in educating the public, as well as generating public support. Major Iowa newspaper and television stations have sent personnel to do stories at release sites with very short notice from us. Local newspaper coverage of releases has also been excellent. A number of radio stations have interviewed ICC personnel about the program. Such coverage has promoted statewide response from citizens who want to become involved with the Barn-owl restoration program. Undoubtedly it has also increased donations to the Nongame Iowa income tax refund Checkoff which funds our program.

FUTURE

Plans for 1984 include placement of 7 Barn-owl breeding pairs in January, several pairs with young in April, and approximately 20 fledglings during summer. Also, in 1984, we hope to place radio transmitters on 3 breeding pairs and 10 fledgling Barn-owls to monitor habitat use, early dispersal movements, and mortality. A graduate student from Iowa State University will be involved full time on this aspect of the program.

CONCLUSION

The success of Iowa’s Common Barn-owl restoration program is greatly dependent on public education and involvement. Much public interest has already been generated, and we need to channel this interest into involvement with building and erecting nest boxes, as well as monitoring these boxes for Barn-owl use.

It is also important that we cooperate with Barn-owl restoration projects in neighboring states such as Missouri and Nebraska. We can learn from each other’s failures and successes, and it is probably only a matter of time before a Barn-owl banded in Iowa shows up in a nest box in Missouri, or vice versa. Cooperation is certainly the key to this program’s success!

ACKNOWLEDGEMENTS

I thank Iowa’s Nongame Biologist, D. A. Newhouse, who initiated the Barn-owl restoration program, and who provided assistance in the final draft of this manuscript. I extend special thanks to my wife, M. Ehresman for being the main editor of this paper as well as providing field assistance and constant moral support. I thank S. Monen for typing this manuscript and for her secretarial work related to the restoration project. I also thank L. Crim and R. Dietz for their field assistance and dedicated care of captive breeding owls. I am grateful to Dallas Center Hy-Line International, the National Animal Disease Center and Iowa State Diagnostic Laboratory, located in Ames, for contributing their excess chicks and mice to supplement our captive owl food source; and I thank R. Lindahl and G. Crim for providing laboratory mice delivery service. I am especially thankful to the following cooperators who provided release sites and/or captive owl care, and whose efforts made Barn-owl releases possible: B. and N. Bakehouse, R. and F. Cooper, C. and K. Froyen, L. and M. Hardin, I. Hardt, C. Hensley and Cass County Conservation Board staff, L. and C. Inman, H. Jensen, L. and N. Link, M. Moe, J. and B. Sabin, E. and M. Schlueter, and B. and J. Wilson. Also, a special thanks goes to R. Minthorn who contributed 10 nest boxes for owls released in Mills County. Finally, I wish to thank the people who have contributed to Iowa’s Nongame income tax refund Checkoff, which funds this project.

LITERATURE CITED

ANDREWS, R. D., J. L. HANSEN, and B. R. OHDE. 1982. Furbearer harvest survey. Iowa Conserv. Comm. Study no. 19.

BECKER, C. 1978. Endangered and threatened wildlife. Ill. Dept. Conserv. 1-4.

BUNN, D. S., A. B. WARBURTON, and R. D. S. WILSON. 1982. The Barn Owl. Vermillion, South Dakota, Buteo Books.

MARTI, C. D., P. W. Wagner, and K. W. DENNE. 1979. Nest boxes for the management of barn owls. Wildl. Soc. Bull. 7(3):145-148.

MC KEEVER, K. 1979. Care and rehabilitation of injured owls. Ontario, Canada, W. F. Rannie.

PETERSEN, L. R. 1979a. Ecology of Great Horned Owls and Red-tailed Hawks in Wisconsin. Wis. Dept. Nat. Resour. Tech. Bull 111:1-95.

_______. 1979b. Status of Barn Owls in Wisconsin. Wis. Dept. Nat. Res. Rep. 1097:1-11.

PIECHOCKI, R. 1960. Uber die winterverluste der schleiereule. (Tyto alba). Vogelwarte 20:274-280.

RATCLIFFE, E. J. 1979. Fly high, run free. London.  Reference not available, cited from Bunn et al. (1982)

ROOSA, D. M. 1977. Endangered Iowa birds (an annotated list of endangered, threatened, extirpated or “status undetermined” birds of Iowa). Iowa Conserv. Comm. Spec. Rep. of Preserves Board, no. 4:1-25.

STEWART, P. A. 1952. Dispersal, breeding behavior, and longevity of banded Barn Owls in North America. Auk 69:227-45.

TAYLOR, S. M. 1978. Michigan’s endangered and threatened species program. Mich. Dept. Nat. Resour. 1-35.

WADDELL, W., and W. C. CRAWFORD, Jr., 1982. Barn Owl recovery program – Missouri and the Midwest. Pp. 74-80 in wildlife rehabilitation (P. Beaver, ed.). Smithtown, New York, Exposition Press, Inc.

WALKER, L. W. 1974. The book of owls. New York, Alfred A. Knopf, Inc.

WAYNE, A. T. 1924. A death trap to the American Barn Owl (Tyto pratincola). Auk 41(2):342.

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[1] (Product of Central Nebraska Packing Company of North Platte. Mention of trade names does not imply endorsement by the ICC.)