Pellets from short-eared owls (Asio flammeus) were collected during March 1990 and January-March 1992 from a former strip-mine area in southern Illinois (USA) and analyzed for prey remains. Microtines comprised 85.8% of 141 skull remains in 1990, and 85.0% of 147 skull remains in 1992. Results were similar to previous studies in Illinois and elsewhere

Feldhamer, George A

Machniak, Angela

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Southern Illinois University CarbondaleOpenSIUCPublications Department of Zoology1993Feeding Habits of Short-eared Owls Overwinteringin Southern IllinoisGeorge A. FeldhamerSouthern Illinois University CarbondaleAngela MachniakSouthern Illinois University CarbondaleFollow this and additional works at: http://opensiuc.lib.siu.edu/zool_pubsPublished in Transactions of the Illinois State Academy of Science, Vol. 86 No. 1 and 2 (1993)This Article is brought to you for free and open access by the Department of Zoology at OpenSIUC. It has been accepted for inclusion in Publicationsby an authorized administrator of OpenSIUC. For more information, please contact opensiuc@lib.siu.edu.Recommended CitationFeldhamer, George A. and Machniak, Angela. "Feeding Habits of Short-eared Owls Overwintering in Southern Illinois." ( Jan 1993).Transactions of the Illinois State Academy of Science(1993), Volume 86, 1 and 2, pp. 79 - 82Feeding Habits of Short-Eared OwlsOverwintering in Southern IllinoisAngela Machniak and George FeldhamerDepartment of ZoologySouthern Illinois UniversityCarbondale, IL 62901ABSTRACTPellets from short-eared owls (Asio flammeus) were collected during March 1990 andJanuary-March 1992 from a former strip-mine area in southern Illinois and analyzed forprey remains.  Microtines comprised 85.8% of 141 skull remains in 1990, and 85.0% of147 skull remains in 1992.  Results were similar to previous studies in Illinois andelsewhere.INTRODUCTIONPeabody Mine is a strip-mine site located about 20 km southeast of Harrisburg, SalineCounty, Illinois, that has not been in operation since 1987.  Short-eared owls have beenfound on the site since 1988, where they roost on the ground in fields of foxtail(Alopecurus carolinianus), broomsedge (Andropogon virginicus), little blue stem(Schizachyrium scoparium), switch grass (Panicum virgatum), and fescue (Festucapratensis).  Little blue stem and switch grass were planted at the site.  Adjacent to theroost site is a 0.5 ha plot of tilled corn and four deep pools of water.  Five short-earedowls occupied the site in 1990, and at least 11 in 1992.  They used the site from lateNovember through mid-March each year.  It was not determined whether the sameindividuals used the area during the two sampling periods.  Pellets were collected from acommunal diurnal roost site each year.  Our objective was to identify prey consumed byshort-eared owls in this area, and contrast any change in frequency of prey speciesoccurrence in 1990 vs. 1992.MATERIALS AND METHODSPellets were collected in March 1990 and represented a 3-month accumulation from fiveshort-eared owls.  Pellets were collected in 1992 at monthly intervals from Januarythrough March when at least 11 short-eared owls were using the site.  Prey remains wereseparated from pellets by hand.  The mandible and cranium was used to identify eachtaxon.  Skulls of prairie voles (Microtus ochrogaster) were differentiated from those ofpine voles (M. pinetorum) on the basis of the anterior border on the fourth triangle of thefirst lower molar (Martin 1974, Martin and Webb 1974).  Because of the low occurrenceof Peromyscus in the samples, no attempt was made to determine species for this taxon.80                                                                                                          RESULTS AND DISCUSSIONRemains of 141 prey items were recovered from 104 pellets collected in 1990 (meannumber of prey items per pellet = 1.36), of which 85.8% were microtines.  In 1992, 147prey items were found in 113 pellets (mean number of prey items per pellet = 1.30), ofwhich 85.0% were microtines.  The same six mammalian taxa were found in 1992 as in1990, and were remarkably similar in frequency (Table 1).  There was no significantdifference for the 1990 vs 1992 sample in the frequency of prey consumed (G-test = 2.53,df = 7,    P > 0.50), and the Shannon-Weiner Diversity Index was the same for each year(Table 1).  Our results are similar to Colvin and Spaulding (1983) who found short-eared owls inOhio consumed 95.4% meadow voles (M. pennsylvanicus).  Clark (1975) reported theproportion of Microtus in the diet of wintering short-eared owls in New York was neverbelow 90%, and this is consistent with other studies on short-eared owls (Snyder andHope 1938, Terres and Jameson 1943, Kirkpatrick and Conway 1947, Weller et al. 1952,Graber 1962, Clark 1972).  In contrast, however, Cahn and Kemp (1930) found short-eared owls in central Illinois took only 29.2% voles.  As in other species of owls (Bunnet al. 1982), short-eared owls do not forage selectively, but take prey opportunistically, inproportion to availability (Clark 1975).  We examined only pellets cast at the roost, andnot pellets cast while the owls were foraging, although there may be "... a difference inpercentage composition [of prey] between field cast pellets and roost cast pellets ..." inshort-eared owls (Clark 1975:11).  Nevertheless, considering roost pellets cast during thewinters of 1990 and 1992, there was temporal consistency in the diet of short-eared owlson the study area, and likely an associated consistency in relative abundance of the smallmammal fauna during this period.ACKNOWLEDGMENTSWe thank Todd Fink, Illinois Department of Conservation, for the 1990 prey remains andfor assistance in all phases of this study.  Judy DeNeal and Heather Rice assisted withcollections, and Peabody Coal Company allowed access to the property.81                                                                                                          LITERATURE CITEDBunn, D. S., A. B. Warburton, and R. D. S. Wilson.  1982.  The barn owl.  Buteo Books,Vermillion, South Dakota.  264 pp.Cahn, A. and J. Kemp.  1930.  On the food of certain owls in east-central Illinois.  Auk 47:323-328.Clark, R. J.  1972.  Pellets of the short-eared owl and marsh hawk compared.  J. Wildl. Manage.36:962-964.Clark, R. J.  1975.  A field study of the short-eared owl, Asio flammeus (Pontoppidan), inNorth America.  Wildl. Monogr. 47:1-67.Colvin, B. and S. Spaulding.  1983.  Winter foraging behavior of short-eared owls (Asioflammeus) in Ohio.  Amer. Midl. Nat. 110:124-128.Graber, R.  1962.  Food and oxygen consumption in three species of owls (Strigidae).  Condor64:473-487.Kirkpatrick, C. and C. Conway.  1947.  The winter foods of some Indiana owls.  Amer. Midl.Nat. 38:755-766.Martin, R. A.  1974.  Fossil mammals from the Coleman IIA fauna, Sumter County. Pp. 35-99in S. D. Webb (ed.).  Pleistocene mammals of Florida.  Univ. Florida Press, Gainesville.  270pp.Martin, R. A. and S. D. Webb.  1974.  Late Pleistocene mammals from the Devil's Den fauna,Levy County. Pp. 114-145 in S. D. Webb (ed.).  Pleistocene mammals of Florida.  Univ.Florida Press, Gainesville.  270 pp.Pielou, E. C.  1966.  The measurement of diversity in different types of biological collections.J. Theoret. Biol. 13:131-144.Snyder, L. L. and C. E. Hope.  1938.  A predator-prey relationship between the short-eared owland the meadow mouse.  Wilson Bull. 45:110-112.Terres, J. K. and E. W. Jameson, Jr.  1943.  Plague of mice as food for short-eared owls.Wilson Bull. 55:131.Weller, M. W., I. C. Adams, Jr., and B. J. Rose.  1955.  Winter roosts of marsh hawks andshort-eared owls in central Missouri.  Wilson Bull. 67:189-193.82                                                                                                          Table 1. Prey remains in short-eared owl pellets collected in 1990 and 1992, from thePeabody Mine area, Saline County, Illinois.     Winter     1990     (n     =    104)       Winter     1992     (n     =    113)Prey     Item       Frequency       %    Frequency       %MAMMALSRodentsPrairie vole(Microtus 77 54.6 75 51.0ochrogaster)Pine vole(Microtus 40 28.4 48 32.6pinetorum)House mouse(Mus 8 5.7 12 8.2musculus)Bog lemming(Synaptomys 4 2.8 2 1.4cooperi)Deer mouse(Peromyscus) 2 1.4 2 1.4InsectivoresLeast shrew(Cryptotisparva) 2 1.4 1 0.7______ ______ ______ ______SUBTOTALMammals 133 94.3 140 95.3BIRDS(Unknownpasserines 8 5.7 7 4.8______ ______ ______ ______TOTAL 141 100.0 147 100.1DiversityIndex (H)a 1.3 1.3a - H = - ∑ pi2 ln pi2, where pi = proportion of each prey item in the total sample(Pielou 1966).       

Feeding Habits of Short-eared Owls Overwintering in Southern Illinois

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Feeding Habits of Short-eared Owls Overwintering in Southern Illinois

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