A Comparison of Raptor Densities and Habitat Use in Kansas Cropland and Rangeland Ecosystems

j. RaptorRes. 34(3):203-209 ¸ 2000 The Raptor ResearchFoundation, Inc.

A COMPARISON OF RAPTOR DENSITIES AND HABITAT USE IN KANSAS CROPLAND AND RANGELAND ECOSYSTEMS

CHRISTOPHER K. WILLIAMS Departmentof WildlifeEcology, University of Wisconsin,Russell Labs, 1630 LindenDrive, Madison, WI 53706-1598 U.S.A.

ROGER D. APPLEGATE Departmentof Wildlifeand Parks,Research and SurveyOffice, P.O. Box 1525, Emporia,KS 66801-1525 U.S.A.

R. SCOTT LUTZ AND DONALD H. RUSCH Departmentof WildlifeEcology, University of Wisconsin,Russell Labs, 1630 LindenDrive, Madison, WI 53706-1598 U.S.A.

ABSTRACT.--Wecounted raptors on line transectsalong roads to assessdensities, species diversity, and habitat selection of winter raptors between cropland and rangeland habitats in eastern Kansas.We conductedcounts every 2 wk betweenSeptember-March 1994-98. Speciesdiversity indices did not differ between the two habitats (P -- 0.15). We calculateddensity estimates and cover type selectionfor Red- tailed Hawks (Buteojamaicensis),Northern Harriers (Circuscyaneus), and American Kestrels(Falco sparverius).Red-tailed Hawks and Northern Harrier densitieswere higher in cropland, while kestreldensities did not differ betweenthe two habitats.All three speciesacross both habitatshad a general preference for idleland habitat. We believe three factors could explain the higher raptor densitiesin cropland: increasedprey abundance,increased visibility of prey associatedwith harvestedagriculture fields, and/ or a higher relative amount of preferred hunting habitat. K•¾WORDS: NorthernHarri• Circuscyaneus; Red-tailed Hawk; Buteojamaicensis; American kestrel; Falco sparverius;cropland; cover type selection; density; line transect;rangeland.

Una comparaci6nde densidadesde avesrapaces y uso de h/tbitat en tierras agricolasy ecosistemasde pastizalesen Kansas RESUMEN.--Contamoslas avesrapaces en transectoslineares a largo de carreteraspara evaluarlas densidades,la diversidadde especiesy la selecci6nde h•tbitat de las rapacesque pasan el invierno entre las tierras agricolasy los h/tbitatsde pastizalesen el este de Kansas.Hicimos conteoscada 2 semanas entre septiembrey marzo 1994-98. Los indices de diversidadde especiesno difirieron entre los dos h/tbitats(P = 0.15). Calculamoslas densidadesy la selecci6nde cobertura para Buteojamaicensis,Circus cyaneus,y Falco sparverius. Las densidades de Buteojamaicensis y Circus cyaneus fueron mayoresen lasfireas de cultivos,mientras que las densidadesde Falcosparverius no difirieron entre los dosh/tbitats. Las tres especiesa lo largo de ambos h/tbitatstuvieron una preferencia general por el h/tbitat de tierras sin trabajar. Creemos que tres factorespueden explicar la mayor densidad en tierras cultivadas;aumento de la abundanciade presas,aumento de la visibilidadde presasasociada alas fireasde tierrascosechadas, y/o a un aumento relativo de la cantidad de h/tbitat de caza. [Traducci6n de Cfisar M/trquez]

EasternKansas is the wintering range for 11 spe- Although there is a large amount of research on cies of diurnal raptors. In addition, three species the basicwinter ecologyof many speciesof raptors of diurnal raptors migrate through eastern Kansas (e.g., Craighead and Craighead 1956, Collopy to wintering and breeding ranges (American Or- 1973, Bohall and Collopy 1984, Collopy and Bild- nithologists' Union 1998). Eastern KansasAudu- stein 1987, Temeles and Wellicome 1992, Ardia bon SocietyChristmas Bird Countsaverage 41-100 and Bildstein 1997), little research has examined individual falconiform birds per count in 1986 the effects of different landuse regimes (e.g., ag- (Johnsgard 1990). riculture or grazing) on winter raptor ecology.

203 204 WILLIAMS ET AL. VOL. 34, No. 3

Consequently,we estimated densities, speciesdi- power poles that could influence raptor abundancewere versity,and habitat selectionof winter raptors in presentalong 50% of the RSA transectand 55% of the CSA transect (Andersen et al. 1985). Transectlength was cropland and rangeland ecosystemsin eastern 31.40 km on CSA and 28.94 km on RSA. We ran transect Kansas. routes every 2 wk between 15 September-31 March 1994-98. With two observationvehicles, each containing STUDY AREAS two individuals, we sampled each route on the same day We conducted raptor surveysin both an agricultural- starting approximately 1 hr after sunrise.At each sight- and rangeland-dominatedlandscape in southern Lyon ing, we stopped the vehicle at approximatelya perpen- County,Kansas, where there wasnarrow transitionzone dicular angle from where the raptor was first observed between rangeland (western) and cropland (eastern) perched or flying. We recorded the species,major land ecosystems.We selectedstudy areas within this transition use the raptor wasoccupying, and estimatedthe distance zone to ensure that the distance between study areas from car to raptor using rangefinders.We estimatedden- would reduce confounding climatic differences yet min- sities with five possible detection functions (HNormal xm•ze migration between study areas. Both study areas Hermite, Uniform Polynomial, HNormal Cosine, Uni- were approximately2849 ha of private land and separat- form Cosine, and Hazard Cosine) using program DIS- ed by 20 km. The cropland study area (CSA) was 3 km TANCE (Laake et al. 1993). The best fit detection func- west of Hartford, Kansas,and the rangeland studyarea tion and density was chosen by program DISTANCE (P (RSA) was7 km westof Olpe, Kansas.Because the study --<0.05). We used repeated measuresANOVA to compare areaswere large, we could not spatiallyreplicate our land- density estimateswithin and among years within study scapes. areas and between study areas. We performed compositionalanalyses for individual METHODS speciesacross all surveyswithin a given year using log- ratio differencesbetween cover type use and availability The percent coverageof covertypes on our studyareas (Aebischer et al. 1993). We consideredcover type use as was calculated areas using aerial photographsfrom 1990 the percent of all cover typesa specieswas observed oc- and ArcView Geographic Information System (Version cupying.We consideredcover type availabilityas the per- 3 1, 1998). The CSA included 49% cropland (e.g., soy- cent of all cover typeswithin the studyarea boundaries. beans, sorghum,corn, and winter wheat), 19% native We defined cover type "selection" as the difference be- hayland,16% nativetallgrass pasture, 12% idle grassland tween cover type use and availability. We first tested (e g., Conservation Reserve Program grasses,grassy wa- whether all cover type selectionwas random using Wilk's terways,roadsides), and 4% woodycover (e.g., treelines, lambda statistic(P <- 0.05). We then used 1-samplet-tests wooded drainage ways).We identified 65 discreteunits to rank the selection of cover types (Aebischer et al. of woodycover on CSA,each measuring on average1.75 1993). If covertype selectionoccurred significantly great- ha Percent coverageof cover typeswithin CSA wassim- er than random, we defined the cover type as "pre- fiar to agriculturalareas within easternLyon County (By- ferred." If cover type selectionoccurred significantlyless ram 1996). than random, we defined the cover type as "avoided." The compositionof RSAwas 72% nativetallgrass pas- To compare relative cover type selectionbetween study ture, 8% hayland,8% idle grassland,8% cropland,and areasamong years,we used 2-wayANOVA. 3% woodycover. We identified 28 discreteunits of woody cover on RSA, each measuring on average 3.05 ha. As RESULTS compared to CSA, woody cover units were larger and more fragmented from each other. Percent coverageof Species diversity indices did not differ among cover types within RSA was similar to rangeland areas yearswithin studyareas (F3.68= 1.51, P = 0.22) or wxthin the Flint Hills region (Kollmorgan and Simonett 1965), and grazing and burning dominated land use betweenstudy areas (F•,68-- 3.04, P -- 0.09) (Table practices(every 1-4 yr). Landownersreported the aver- 1). Due to low sample sizes (mean N ( 10 per age annual grazingpressure on RSAwas I steer/0.81 ha, year), we only estimateddensity and cover type se- whxch was considered overgrazed (Launchbaugh and lection for Red-tailed Hawks (Buteojamaicensis, Owensby1978, Owensbyet al. 1988). CSA: mean N = 127, RSA: mean N = 127), North- To measure relative diurnal raptor speciesdiversity between studyareas, we used the Shannon-Wienerdiversity ern Harriers (Circuscyaneus, CSA: mean N = 36, xndex (Zar 1984) on raw observationsof species.By using RSA: mean N = 20), and American Kestrels (Falco raw observations,we assumeddetectability functions were sparverius,CSA: mean N = 18, RSA:mean N = 19). equal acrossall speciesand individuals.We used a two- Red-tailed Hawk densities did not differ within way ANOVA (P --< 0.05) to compare diversityindices among years and between study areas. and amongyears in both CSAor RSA (F •,6= 2.79, We establisheda single line transect on roads travers- P = 0.15), so data were pooled within each study ing CSA and RSA (Andersenet al. 1985). An assumption area. Densities were three times higher on CSA of line transect sampling is that the distribution of ob- than on RSA (F•.6 = 14.81, P (0.01) (Table 2). served speciesis not influenced by the transect lines (Buckland et al. 1993). We feel any violation of this as- Habitat use did not differ amongyears within both sumption wasreduced becauseroads were generallyone studyareas (F3.70( 1.42, P ) 0.24) and waspooled lane, unpaved, and had low traffic and telephone and within studyareas. On both studyareas, overall cov- SEPTEMBER2000 KANSAS RAPTOR ECOLOGY 205 206 WILLIAMS ET AL. VOL. 34, NO. 3

er type selection departed from random selection (CSA: A < 0.53, X24 > 44.00, P < 0.01). On CSA, Red-tailed Hawks preferred idle grassland and woody cover (t40> 2.33, P < 0.03) while avoiding hayland, cropland, and pasture (t40 > 3.81, P < 0.01) (Fig. 1). On RSA, they used pastureequally with availability (•6 = 1.95, P = 0.06), preferred woody cover (t36 = 12.48, P < 0.01), and avoided pasture, hayland, and cropland (t42 > 3.91, P < 0.01) (Fig. 1). We found Red-tailed Hawks selectedhayland and croplandequally between CSA and RSA (F•,70 < 0.47, P > 0.50). However,they selectedpasture and woody cover less on RSA than CSA (FL70 > 5.48, P • 0.02) while they selectedidle grassland more on RSA than CSA (F3,70= 28.34, P < 0.01). Northern Harrier densities did not differ within or among yearsin both CSA or RSA (FL6 = 0.62, P = 0.46), so data were pooled within studyareas. Densitieswere twice as high on CSA than on RSA (FL6 --- 4.22, P = 0.09) (Table 2). Habitat use did not differ among years in either study area (F3,s8 • 1.53, P • 0.22) and waspooled within studyareas. On CSA overall cover type selection did not depart from random selection(CSA: A = 0.96, X2 = 8.26, P • 0.08) whereas selection on RSA did (RSA: A = 0.73, X24= 12.87, P < 0.01). On RSA, Northern Harriers used idle grasslandequally with its availability(t28 = 1.00, P = 0.32) while avoiding woody cover and hayland (t28 • 2.86, P • 0.01) and preferring pastureand cropland (t28• 2.58, P < 0.02) (Fig. 1). We found Northern Harriers selected hayland, idle grassland,woody cover,and cropland equally betweenCSA and RSA (FLs8 < 3.45, P > 0.07). However,they selectedpasture more on RSA than CSA (FL58= 9.17, P < 0.01). American Kestrel densities did not differ within or among yearsin both CSA or RSA (FL6 = 1.90, P = 0.22) or betweenstudy areas (F•.6= 0.02, P = 0.90) (Table 2). For kestrelson both study areas, habitat use did not differ among years (F•,4• < 2.71,P > 0.06) and waspooled within study areas. On both study areas, overall cover type selection departedfrom random selection(A < 0.56, •(24 > 24.01, P < 0.01, RSA). On CSA, kestrels used idle grasslandand cropland equally with their availability (t,24< 1.33, P > 0.20), preferred woodycover (t,24= 6.48, P < 0.01), and avoidedpasture and hayland (t,24> 3.01, P < 0.01) (Fig. 1). On RSA, they used pasture and cropland equallywith their availability(t2• < 1.43,P > 0.17), preferredwoody SEPTEMBER2000 IL•4sAs R•TOR ECOLOGY 207

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[] CROPLAND STUDY AREA -6 ß RANGELAND STUDY AREA Figure 1. Relativecover type selectiongiven availability(_SE) by Red-tailedHawks, Northern Harriers, and Amer- ican Kestrelsin CSA and RSA, Lyon County,Kansas, 1994-98. Log-ratiocover type selectionvalues above zero indicate relative preference whereasvalues below zero indicate relative avoidance. 208 WILLIAMS ET AL. VOL. 34, NO. 3 cover (t24 = 5.36, P < 0.01), and avoided hayland swainsoni)and Ferruginous Hawks (Buteoregalis) and idle grassland(t24 > 14.30, P < 0.01) (Fig. 1). wasdetermined more by the presenceof prey pro- We found that American Kestrelsselected hay- tective cover than by prey density. Therefore, land, woody cover, and cropland equally between hawks were present in habitat, such as harvested CSA and RSA (F1,41< 3.20, P > 0.08). However, agriculture,where prey wasmore vulnerable.How- they selected pasture more on RSA than CSA ever, Preston (1990) and Bildstein (1987) found (F1.4•= 23.05, P < 0.01) and they selected idle Red-tailed Hawks and Northern Harriers tended to grasslandless on RSA than CSA (F1.4•= 4.25, P > avoid harvested agriculture and Preston (1990) 0.05) (Fig. 1). noted this might be due to lower prey densitiesin these patches. Becauseour findings that raptors DISCUSSION avoided harvested agriculture generally support In the four years of our study,we found stable Preston (1990) and Bildstein (1987), we question populations of Red-tailed Hawks, Northern Harri- whether this hypothesiscould explain higher den- ers, and American Kestrels.While long-term data sities on CSA. (1959-88) from Kansas Christmas Bird Counts Alternatively, Newton (1979) suggested the (Sauer et al. 1996) suggestthat Red-tailed Hawk shortageof perching sitesinfluence winter raptor populationshave remained stable,they alsofound density.Relative abundanceof perching treesnext Northern Harriers have declined while American to open hunting areas have been found to be an Kestrels have increased. important regulating factor for both Red-tailed Our finding that local densities of Red-tailed Hawks and Northern Harriers (Preston and Beane Hawks and Northern Harriers were higher on CSA 1993, MacWhirter and Bildstein 1996). Research in is similar to Fitch et al. (1973) who found higher Kansasby Cox (1976) and by us indicatedthe use raptor populations in eastern Kansas (similar to of woody cover is important habitat for Red-tailed CSA) than in the Flint Hills Region (RSA) between Hawks and Northern Harriers. We believeit is pos- 1950-63. We believe severalfactors could explain sible that a larger availabilityof potential hunting higher raptor densities on CSA including prey areas, associatedwith woody cover,could have pro- abundance, prey visibility, and/or the relative moted higher densitieson CSA. amount of preferred hunting habitat. The abundanceof prey and the availabilityof Relative local prey abundance can affect local suitable habitat for roosting and perching affect raptor densities (Craighead and Craighead 1956, raptor populations.Consequently, landuse practic- Grant et al. 1991). In a study of Eurasian Kestrels es can have an impact on raptors. Our resultsonly (Falcotinnunculus) in cropland and grassland,Vil- indicate relationshipson our studyareas. However, lage (1989) found kestrel numbers were higher we encouragemanagers to considerthese relation- and less variable in cropland ecosystemsbecause shipsand addresswhether they could applyto oth- of the greater diversityof stableprey populations. er agricultural and rangeland systems. Both Red-tailed Hawk and Northern Harrier ACKNOWLEDGMENTS choice of prey includes small- and medium-sized mammals (mainly rodents), reptiles and small- to We thank G. Horak, J. Stephen, R. Powers,M. Paradise, medium-sized birds (Preston and Beane 1993, K. Church, C. Roy, and A. Schleicher for assistingwith counts; and J.R. Cary and M.L. Williams who provided MacWhirter and Bildstein 1996). Additionally,both data analysisadvice. The KansasDepartment of Wildlife are known to consume Northern Bobwhite (Coli- and Parks,Federal Aid ProjectNo. W-39-R,Wisconsin Co- nus virginianus)(Errington and Breckinridge1938, operative Wildlife ResearchUnit, the University of Wis- Selleck and Glading 1943). Williams (1996) found consin, Emporia Area Chapter of Quail Unlimited, and the Max McGraw Foundation helped fund this research. that Northern Bobwhitedensities were significantly higher on the CSA than on the RSA, potentially LITERATURE CITED indicatinga larger prey baseon CSA,which in turn AEBISCHER,NJ., P.A. ROBERTSONAND R.E. KENWARD. could promote a higher abundanceof raptors. 1993. Gompositionalanalysis of habitat use from ani- Secondly,raptor densitiescould have been high- mal radio-trackingdata. Ecology 74:1313-1325. er on CSA because of the increased visibility of AMERICAN ORNITHOLOGISTS' UNION. 1998. Check-list of prey associatedwith harvested agriculture fields. North American birds, 7th ed. Am. Orinthol. Union, Wakeley (1978) and Bechard (1982) found that se- Washington,DG U.S.A. lection of hunting sitesby Swainson'sHawks (Buteo ANDERSEN,D.E., OJ. RONGSTAD,AND W.R. MYrTON.1985. SEPTEMBER2000 KANSASRAPTOR ECOLOGY 209

Line transect analysis of raptor abundance along Chase County, Kansas.Ann. Assoc.Am. Geog.55:260- roads. Wildl. Soc. Bull. 13:533-539. 290. ARDIA, D.R. AND K.L. BILDSTEIN.1997. Sex-related differ- LAAKE,J.L., S.T. BUCKLAND,D.R. ANDERSON,AND K P encesin habitat selectionin wintering American kes- BURNHAM.1993. DISTANCE user'sguide V2.0. Colo- trels,Falco sparverius. Anim. Behav.53:1305-1311. rado Coop. Fish Wildl. Res. Unit, Colorado State BECHARD,MJ. 1982. Effect of vegetativecover on forag- Univ., Fort Collins, CO U.S.A. ing siteselection by Swainson'sHawk. Condor84:153- LAUNCHBAUGH,J.L. AND C.E. OWENSBY.1978. Kansas 159. rangelands--their management based on a half cen- BILDSTEIN,K.L. 1987. Behavioral ecology of Red-tailed tury of research.Kansas Agric. Exp. StationBull. 622. Hawks (Buteojamaicensis),Rough-legged Hawks (Buteo Manhattan, KS U.S.A. lagopus),Northern Harriers (Circus cyaneus),and MACWHIRTER, R.B. AND K.L. BILDSTEIN. 1996. Northern American Kestrels (Falcosparverius) in south central Harrier ( Circuscyaneus). In A. Poole and F. Gill lEDs ], Ohio. Ohio Biol. Surv. Biol. Notes 18. The birds of North America, No. 210. The Academy BOHALL,P.G. AND M.W. COLLOPY.1984. Seasonal abun- of Natural Sciences,Philadelphia, PA, and The Anner- dance, habitat use, and perch sitesof four raptor spe- ican Ornithologists'Union, Washington,DC U.S.A. cies in north-centralFlorida. J. Field.Ornithol. 55:181- NEWTON,I. 1979. Population ecology of raptors. Buteo 189. Books, Vermillion, SD U.S.A. BUCI4LAND,S.T., D.R. ANDERSON,K.P. BURNHAM,AND J.L. OWENSBY,C.E., R. COCHP,AN, AND E.F. SMITH. 1988. Stock- LAAKE.1993. Distance sampling: estimating abun- ing rate effectson intensive-earlystocked Flint Hills dance of biologicalpopulations. Chapman and Hall, bluestemrange. J. RangeManage. 41:483-487. London, U.K. PRESTON,C.R. 1990. Distribution of raptor foraging •n BYRAM,T.S. 1996. Kansasfarm facts. KansasDep. Agric. relation to prey biomassand habitat structure.Condor Topeka, KS U.S.A. 92:107-112. COLLOPY,M.W. 1973. Predatory efficiencyof American --AND R.D. BEANE.1993. Red-tailed Hawk (Buteoya- Kestrelswintering in northwesternCalifornia. Raptor maicensis).In A. Poole and E Gill lEDS.], The birds of Res. 7:25-31. North America, No. 52. The Academyof Natural Sci- --AND K.L. BILDSTEIN.1987. Foraging behavior of ences,Philadelphia, PA and The American Ornithol- Northern Harriers wintering in southeasternsalt and ogists'Union, Washington,DC U.S.A. freshwater marshes. Auk 104:11-16. SAUER,J.R., S. SCHWARTZ,AND B. HOOVER.1996. The Cox, J.A. 1976. Winter ecologyof hawksin easternKan- ChristmasBird Count home page. Version 95.1. Pa- sas. M.S. thesis, Univ. Kansas, Lawrence, KS U.S.A. tuxent Wildlife Research Center, Laurel, MD U.S.A. CRAIGHEAD,JJ. AND F.C. CRAIGHEAD,JR. 1956. Hawks, SELLECK,D.M. AND B. GLADING. 1943. Food habits of nest- owls,and wildlife. Stackpole,New York, NY U.S.A. ing Barn Owls and marshhawks at Dune Lakes,Cal- ERRINGTON,P.L. ANDw.J. BRECKINRIDGE.1938. Food hab- ifornia, as determined by the "cage nest" method its of buteo hawks in north-central United States. Wil- Calif. Fish Game20:122-131. son Bull. 50:113-121. TEMELES,EJ. ANDT.I. WELLICOME.1992. Weather-depen- FITCH, H.S., H.A. STEPHANS,AND R.O. BARE.1973. Road dent kleptoparasitism and aggressionin a raptor counts of hawks in Kansas. Bull. Kans. Ornithol. So& guild. Auk 109:920-923. 24:33-35. VILLAGE,A. 1989. Factorslimiting Europeankestrel Falco FULLER,M.R., C.J. HENNY,AND P.B. WOOD. 1995. Raptors. tinnunculus numbers in different habitats. In B.-U. In E.T. LaRoe, G.S. Farris, C.E. Puckett, P.D. Doran, Meyburg and R.D. Chancellor [EDS.],Raptors in the and MJ. Mac [EI•s.], Our living resources:a report to modern world. World Working Group of Birdsof Prey the nation on the distribution, abundance, and health and Owls, Berlin, Germany. of U.S. plants, animals, and ecosystems.U.S. Dep. In- WAKELEY,J.S. 1978. Factorsaffecting the use of hunting ter., Natl. Biol. Serv., Washington,DC U.S.A. sitesby FerruginousHawks. Condor 80:327-333. GRANT,C.V., B.B. STEELE,AND R.L. BA•,JR. 1991. Raptor WILLIAMS,C.K. 1996. Winter ecology of the northern population dynamicsin Utah's Uinta Basin:the im- bobwhite in Kansascropland and rangeland ecosys- portanceof food resource.Southwest. Nat. 36:265-280. tems. M.S. thesis, Univ. Wisconsin, Madison, WI JOHNSGAP,D, P.A. 1990. Hawks, eagles,and falcons of U.S.A. North America. Smithsonian Institution Press, Wash- ZAR,J.H. 1984. Biostatisticalanalysis. Prentice Hall. En- ington, DC U.S.A. glewood Cliffs, NJ U.S.A. KOLLMORGAN,W.M. AND D.$. SIMONETT.1965. Grazing operations in the Flint Hills--bluestem pasturesof Received 30 October 1999; accepted 22 May 2000