Roadside playback surveys of Eastern Screech-Owls were conducted each spring and fall from September 1984 through April 1986 in Summit Township, Marion County, Iowa. An average of 18 screech-owls were located during each survey, often near riparian woodland. Screech-owl population densities (0.1-0.2 owls/km2) were comparable to those in other regions

Bowles, John B.

Geus, David E.

English

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Relative Abundance of Eastern Screech-Owls in a South-Central Iowa Township

University of Northern Iowa

The Journal of the Iowa Academy of Science: JIASVolume 98 | Number Article 131991Relative Abundance of Eastern Screech-Owls in aSouth-Central Iowa TownshipDavid E. GeusIowa State UniversityJohn B. BowlesCentral CollegeCopyright © Copyright 1991 by the Iowa Academy of Science, Inc.Follow this and additional works at: http://scholarworks.uni.edu/jiasPart of the Anthropology Commons, Life Sciences Commons, Physical Sciences andMathematics Commons, and the Science and Mathematics Education CommonsThis Research is brought to you for free and open access by UNI ScholarWorks. It has been accepted for inclusion in The Journal of the Iowa Academyof Science: JIAS by an authorized editor of UNI ScholarWorks. For more information, please contact scholarworks@uni.edu.Recommended CitationGeus, David E. and Bowles, John B. (1991) "Relative Abundance of Eastern Screech-Owls in a South-Central Iowa Township," TheJournal of the Iowa Academy of Science: JIAS: Vol. 98: No. 2 , Article 13.Available at: http://scholarworks.uni.edu/jias/vol98/iss2/13]our. Iowa Acad. Sci. 98(2):91-92, 1991 Relative Abundance of Eastern Screech-Owls m a South-Central Iowa Township DAVID W. DE GEUS 1 and JOHN B. BOWLES2 Roadside playback surveys of Eastern Screech-Owls were conducted each spring and fall from September 1984 through April 1986 in Summit Township, Marion County, Iowa. An average of 18 screech-owls were located during each survey, often near riparian woodland. Screech-owl population densities (0.1-0.2 owls/km2) were comparable co chose in ocher regions. INDEX DESCRIPTORS: Eastern Screech-Owl, playback census, owl population density The Eastern Screech-Owl (Otus asio) is widely distributed in mosaics of woodland and meadow which characterize much of the eastern United States (Bent 1938). Although considered a common, permanent resident in Iowa (Dinsmore et al. 1984), little is known about its present state-wide status. The only previously published account of a systematic survey from Iowa reported that 5 of 3 1 ( 15 % ) sites surveyed contained screech-owls, but provided no density estimate (Bakehouse 1986). To provide more information on the owl's present status in Iowa, we conducted four roadside surveys between September 1984 and April 1986 in a south-central Iowa township. These surveys were conducted concurrently with a nest box introduc-tion study in the same township. STUDY AREA AND METHODS The study was conducted in Summit Township (T-77N, R19W), Marion County, Iowa. Woodland comprises 14.3% of this 103 km2 township and consists of small woodlots found on both farmsteads and untilled land along streams and steep hillsides. The remainder of the area is largely in rowcrops, i.e., corn and soybeans. The township is increasingly wooded toward Lake Red Rock, the southern boun-dary. Screech-owls were counted once during fall (September - October) and spring (February - April), beginning in 1984 and ending in 1986 (Table 1). Sixty screech-owl nest boxes were placed in the township between the fall 1984 and spring 1985 counts. At least one box was present in each 259 ha section. The modified road-count technique CT. Mosher, pers. comm.) used in this study involved playing taped screech-owl calls between 2400 -0600 H over an 8-ohm speaker at nearly 100 decibels. A midnight-to-dawn period was chosen over early evening to minimize interfer-ence from automobile traffic. A Panasonic cassette player, Fanon public address loudspeaker, and screech-owl tape from John Stuart Wildlife Calls (Waco, Texas) were used to broadcast calls at locations spaced at 0.85-km intervals on all roads. Smith et al. (1987) determined that intervals of 0. 7-1. 2 km were appropriate for screech-owl counts. Screech-owl responses re-ceived within a 10-min period of alternate broadcast and silence were plotted on a topographic map. Observations were postponed or ended if wind speed was > 16 kmph or in inclement weather. Variable weather conditions and other activities of the observer necessitated spreading the 4 nights required for coverage of the study area over a 3-4 wk period. RESULTS AND DISCUSSION Relative Population Size. We recorded 73 screech-owl responses overall, and an average of 18 screech-owls were located per survey (Table 1). Owl density was similar to call-playback estimates from areas with comparable 'Department of Animal Ecology, Iowa Scace University, Ames, Iowa 50011 2Department of Biology, Central College, Pella, Iowa 50219 amounts of woodland cover. Cink (1975) found 0. 15 screech-owls/ km2 in a 16.8% wooded area in northeastern Kansas in spring 1974. However, Nowicki (1974) reported a fall population of 0.88 owls/ km2 in a Michigan township with 23% woodland. Similarly, Smith et al. (1987) found 0.63-1.41 owls/km2 in suburban-rural southern Connecticut, with 80% woodland. These studies suggest that screech-owl numbers are determined by the amount of woodland present. The call-playback technique has been proven to provide estimates within 15 to 30% of actual screech-owl and other Strigiform populations (Fuller and Mosher 1981, Smith et al. 1987). We, therefore, believe that our estimates approximated the actual screech-owl population within the township. However, the .length of time between counts within a season in our study may have allowed movement between areas. We did not account for all factors known to negatively affect screech-owl responses, although we attempted to minimize effects of wind and road noise since both adversely effect the ability to detect the screech-owl's low volume calls (Carpenter 1987, Smith et al. 1987). Screech-owl responsiveness also has been shown to decrease sharply during the spring (Smith 1987, Carpenter 1987), however, since our surveys were not repeated during each season we could not evaluate seasonal or yearly differences. Habitat Use. Of the 73 total screech-owls responses, 53 responded from wood-lands adjacent to small streams or bodies of water. The other 20 were never more than 0.43 km from either a stream or lake. Screech-owls generally avoided cultivated fields, farmsteads, and dense mature timber stands, staying closer to non-isolated stands of immature American elms ( U Imus americana) and sandbar willows (Salix interior) and mature, but open, oak (Quercus spp.) and hickory (Carya spp.) woodlots near small streams. Radio-telemetry studies also have demonstrated that screech-owls prefer deciduous edge habitat near small streams (Ellison 1980; Smith and Gilbert 1984). Table 1. Relative abundance of Eastern Screech-owls in Summit Township, Marion County, Iowa. Survey Number of Number of date stations owls Owls/station Owls/km2 Sept.-Oct. 106 13 0.1 0.1 1984 Feb.-Mar. 116 19 0.2 0.2 1985 Sept.-Oct. 119 24 0.2 0.2 1985 Mar.-Apr. 115 17 0.2 0.2 1986 92 ]OUR. IOWA ACAD. SCI. 98(1991) ACKNOWLEDGEMENTS This study was funded by the Iowa Department of Natural Resources Nongame Wildlife Program; with money derived from the Chickadee Checkoff for nongame wildlife. We thank D. Reeves and D. Roosa for providing advice and guidance throughout the project andJ.J. Dinsmore, L.B. Best, S.N. Wiemeyer, ER. Gelbach, C.D. Marti and T.H. Kent for providing criticism of earlier drafts of this manuscript. REFERENCES BAKEHOUSE, J. 1986. Eastern Screech-Owl survey in Mills County. Iowa Bird Life 56:80. BENT, A.C. 1938. Life histories of North American birds of prey. Part 2: hawks, falcons, caracaras, owls. U.S. Natl. Mus. Bull. 170. CARPENTER, T. W. 1987. Effects of environmental variables on responses ofEastern Screech Owls to playback. Pages 277-280 In R.W. Nero, R.J. Clark, R.J. Knapton, and R.H. Hamre, Eds. Proceedings of the symposium on the biology and conservation of northern forest owls. USDA For. Serv. Gen. Tech. Rep. RM-142, Rocky Mnt. For. and Range Exp. Stn. Fort Collins, CO. CINK, C.L. 1975. Population densities of screech owls in Northeastern Kansas. Kfinsas Ornithol. Soc. Bull. 26: 13-16. DINSMORE,].]., T.H. KENT, D. KOENIG, P.C. PETERSON, and D.M. ROOSA. 1984. Iowa birds. Iowa State Univ. Press. ELLISON, P.T. 1980. Habitat use by resident screech owls (Otus asio). M.S. Thesis, Univ. Massachusetts, Amherst. FULLER, M.R. and J.A. MOSHER. 1981. Methods in detecting and counting captors: a review. Studies Avian Biol. 6:235-246. NOWICKI, T. 1974. A census of screech owls (Otus asio) using tape recorded calls. jack-Pine Warbler 52:98-10 l. SMITH, D.G. 1987. Owl census techniques. Pages 304-307 In R.W. Nero, R.J. Clark, R.J. Knapton, and R.H. Hamre, Eds. Proceedings of the symposium on the biology and conservation of northern forest owls. USDA For. Serv. Gen. Tech. Rep. RM-142, Rocky Mnt. For. and Range Exp. Stn. Fort Collins, CO. SMITH, D.G., A. DEVINE, and D. WALSH. 1987. Censusing screech owls in southern Connecticut. Pages 255-267 In R. W. Nero, R.J. Clark, R.J. Knapton, and R.H. Hamre, Eds. Proceedings of the symposium on the biology and conservation of northern forest owls. USDA For. Serv. Gen. Tech. Rep. RM-142, Rocky Mnt. for. and Range Exp. Sm. Fort Collins, CO. SMITH, D.G. and R. GILBERT. 1984. Eastern Screech-Owl home range and use of suburban habitats in southern Connecticut.]. Field Ornithol. 55:322-329. 

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Relative Abundance of Eastern Screech-Owls in a South-Central Iowa Township

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