j. Raptor Res. 26(2):66-73 ¸ 1992 The Raptor ResearchFoundation, Inc.

PREY USE BY EASTERN SCREECH-OWLS: SEASONAL VARIATION IN CENTRAL KENTUCKY AND A REVIEW OF PREVIOUS STUDIES

GARY RITCHISON AND PAUL M. CAVANAGH 1 Departmentof BiologicalSciences, Eastern Kentucky University, Richmond, KY dOd75

ABSTRACT.--Weexamined prey useby EasternScreech-Owls (Otus asio) in centralKentucky and reviewed the resultsof previousstudies. Invertebrates and mammals were the mostcommon prey in centralKentucky, with mammalsand birds contributingthe mostbiomass. Although prey useby screech-owlsvaried among other locations,small mammalsor birds always contributedthe mostbiomass. In central Kentuckyand at other locations,invertebrates were frequently used during the breedingseason. However, the small size of invertebrateslimited their contributionto total prey biomass.Although capableof killing prey with massesgreater than 100 g, screech-owlstypically usedmuch smaller prey (• = 28.3 g). The mean massof prey taken by screech-owlsduring the breedingperiod (• = 24.6 g) was lower than during the non-breedingperiod (• = 31.8 g), a result of the increasedavailability and use of smaller prey (e.g., invertebrates)during the breeding period.

Presascazadas por tecolotesde la especieOtus asio: variaci6n estacional en Kentucky central,y una revisi6n de estudiosprevios EXTRACTO.--Hemosexaminado el usode las presaspor tecolotesOtus asio en Kentucky central,y hemos revisadolos resultadosde estudiosanteriores. Mamlferos e invertebradosfueron las presasmils comunes en Kentucky central. La biomasaestuvo compuesta en su mayorla por mamlferosy aves.Aunque las presasdel O. asiovariaron segfin los sitios de caza,los pequefios mamlferos y las avessiempre contribuyeron mayormentea la biomasa.En Kentucky centralyen otrossitlos, los invertebradosfueron frecuentemente cazadosdurante la estaci6nde reproducci6n;sin embargo, la pequefia dimensi6n de fistoslimit6 su contribuci6na la biomasade presatotal. Aunque tienen capacidadpara matar presascon una masa de mils de 100 g de peso,estos tecolotes cazaron presas tlpicamente mils pequefias(• = 28.3 g). La masa media de la presacogida por el O. asiodurante el perlodoreproductor (• = 24.6 g) fue menor que la de la presadel periodono reproductor(• = 31.8 g). Esto es resultadodel aumentoen la disponibilidadde presasmils pequefias(e.g., invertebrados)durante el perlodode reproducci6n. [Traducci6n de Eudoxio Paredes-Ruiz]

Although Eastern Screech-Owls(Otus asio) are The objectiveof our study was to examine prey amongthe mostwidespread raptors in easternNorth use, both in terms of occurrenceand biomass,by America (Johnsgard1988), relatively few data are EasternScreech-Owls. We provideinformation con- available concerningtheir food habits (Marti and cerningprey use in central Kentucky and compare Hogue 1979). Most studieshave beenconducted in our results with those published previously. Data the northern United States and most authors have from previousstudies were reanalyzed,converting only reportedthe percentageof occurrenceof each occurrencedata into biomassdata, sothat occurrence prey category.Using frequencydata to draw con- and biomassdata couldbe compared.We soughtto clusionsabout the relative importance of various determinethe extentto which prey use by screech- prey may be misleading.Although suchdata may owls varied with geographiclocation and with time provideinformation about the relative impacta rap- of year. tor has upon prey species,biomass determination METHODS AND MATERIALS may give a more accurateevaluation of the relative Prey Use by Screech-Owlsin Central Kentucky. We importanceof preyspecies to theraptor (Marti 1987). determinedprey useby identifyingthe remainsof prey in pellets (N = 351) and nest debris (N = 9 nests),and by identifyingcached items. Pelletsand nestdebris were col- • Present address:Department of Forestry and Wildlife lectedfrom nestsand roostsites at the Central Kentucky Management, 204 Holdsworth Hall, University of Mas- Wildlife ManagementArea, Madison County,Kentucky, sachusetts,Amherst, MA 01003. betweenSeptember 1985 and August 1986. Pellets were

66 JUNE 1992 SCREECH-OWLPREY USE 67 collectedfrom open roostsites either on or one day after 671 prey items(Table 1). The numberof prey items the day of use.Prey remainsin nestsand nestboxes were from the five prey groups (invertebrates,fish, am- collectedonly when the site was vacant.Nest debriswas phibians,birds, and mammals)varied significantly collectedfrom each nest site in May 1986 afteryoung owls left the nest. (X2 = 865.7, df = 4, P < 0.0001), with invertebrates We identified and quantified most vertebratesusing and mammals being most numerous. Crayfish and skulls and most invertebratesusing head capsules.Some beetles were the most common invertebrate prey. mammalsand birds were identifiedusing hair and feath- Short-tailed shrews (Blarina brevicauda),voles (Mz- ers,and theseprey were quantifiedby assumingthe fewest possiblenumber of individuals (e.g., feathers from one crotusspp.), and mice (Peromyscusspp.) were the specieswere assumedto representone individual).Cray- mostcommon mammalian prey. Mammals contrib- fish remains in pelletswere highly fragmentedso we as- uted the most biomass (65.9%), followed by birds sumedthat a pellet containingcrayfish contained one in- (19.8%) and invertebrates (12.8%; Table 1). d•vidual.All preyitems were identifiedto the lowestpossible Prey usevaried significantly by period(X 2 = 27.95, taxonomiccategory. We used Chi-square analysesto test for differencesin frequencyof use of different prey (in- df = 4, P < 0.0005), with more mammals taken by vertebrates,fish, amphibians, birds and mammals), and screech-owlsduring the non-breeding period and to test for differencesin prey use between the breeding more invertebratestaken during the breedingperiod (March throughAugust) and non-breedingperiods (Sep- (this study;Table 2). Birds, fish, and amphibians temberthrough February). Estimating the Mass of Prey Items. The massof some were taken in similar frequenciesduring the two prey was estimatedby weighing individualscaptured on periods.Mammals contributedmore biomass during or near our study area (e.g., several invertebratesand the non-breeding(75.5%) than the breedingperiod severalspecies of salamanders).Most estimates,however, (61.6%; Table 2). Despite being the most common were taken from the literature (Craigheadand Craighead 1956, Burt and Grossenheider 1964, Carlander 1969, Bar- prey duringthe breedingperiod (63.5% of all prey), bour and Davis 1974, Marti 1974, Clench and Leberman invertebratescontributed only 15.5%of the total prey 1978, Trautman 1981, Steenhof 1983, Dunning 1984, biomass(Table 1). During the non-breedingperiod, Kellner and Ritchison1985). When the massof a species invertebratescontributed 7.7% of the total prey bio- or group was presentedas a range (e.g., Burt and Gros- mass(this study; Table 2). senheider 1964), we used the midpoint as the estimated mass.The massof someprey (e.g., unidentifiedthrush) Prey Use by Screech-Owls: a Review. Infor- wasestimated based on the massesof closelyrelated species mation concerningprey usewas obtainedfrom elev- (e.g., the mean massof all thrush species).Although the en studies (Table 2). Six were conducted in the massof prey may vary with sex, age, and geographical northernpart of the screech-owl'srange (Ohio, Wis- location, it was not possibleto adjust for these variables. Thus, the same estimate of mass was used for all individ- consin,Illinois, New York and two in Michigan), uals of a particular prey speciesor category,regardless of four in the middle (Missouri, Tennessee and two in the geographiclocation of the study. The massof some Kentucky),and only one in the southernpart (Ar- preyitems was potentially (i.e., for olderindividuals) greater kansas).These studiesreported a total of 4917 prey than that of an adult screech-owl(e.g., bluegill Lepomis items, including 20 speciesof mammals, 73 species rnacrochirusand Norway Rat Rattus norvegicus).We as- sumedthat screech-owlswould not take a prey item with of birds, 1 speciesof reptile, 8 speciesof amphibians, a mass larger than their own (mean = 167 g for males and 9 speciesof fish. Although most invertebrates and 194 g for females;Henny and VanCamp 1979) and were not identifiedto species,35 families and genera assignedthese potentially large prey itemsa massof 150 g. were reportedas screech-owlprey. Amongthe major Terminology. Previous investigatorshave examined seasonalvariation in prey use by screech-owls,however, prey groups,mammals (60.9%) were taken most theseinvestigators have delimited seasons in differentways. frequently, followed by invertebrates(22.9%) and We divided the year into two periods:breeding (March birds (14.4%; Table 2). Mammals (73.7%) and birds through August) and non-breeding(September through (19.5%) contributed the most biomass (Table 2). February). Thus, the breedingperiod includes the "nest- Invertebratesmade up only 1.7% of the prey biomass ing season"(Craighead and Craighead1956, VanCamp and Henny 1975) and "spring" (Duley 1979), while the (Table 2). non-breedingperiod includes the "winter" (Craigheadand Rodents(93.6%) were the most frequently taken Craighead1956, Duley 1979),"fall andwinter" (VanCamp mammalian prey of screech-owls,followed by in- and Henny 1975), and the "late fall and winter" (Cahn sectivores(6.1%) and bats (0.2%). Voles (Microtus and Kemp 1930). spp., 69.2% of rodent prey) and mice (Peromyscus RESULTS spp., 17.4% of rodent prey) were the most common Prey Use by Screech-Owlsin Central Ken- rodent prey of screech-owls.Most avian prey were tucky. Pellets,nest debris, and nestboxes yielded passerines(95.3%), largely in the families Emberi- 68 G^R¾RITCHISON AND P^UL M. CAVANAGH VOL. 26, NO. 2

Table 1. Prey usedby EasternScreech-Owls in centralKentucky.

OCCURRENCE BIOMASS

PREY N % GRAMS

Mammals Blarina brevicauda 49 7.3 1127.0 11.2 Cryptotisparva 7 1.0 42.0 0.4 Unident. shrew 3 0.3 54.0 0.5 Pipistrellussubflavus 1 0.1 5.0 < 0.1 Glaucornysvolans 2 0.3 128.0 1.3 Reithrodontornyshurnulis 1 0.1 12.0 0.1 Peromyscusleucopus 3 0.3 66.0 0.7 Peromyscusspp. 39 5.8 858.0 8.5 Microtuspennsylvanicus 17 2.5 629.0 6.3 Microtus ochrogaster 12 1.8 516.0 5.1 Microtus spp. 28 4.2 1120.0 11.1 Rattus norvegicus 1 0.1 150.0 1.5 Mus musculus 11 1.6 209.0 2.1 Unident. cricetid/murid 39 5.8 1092.0 10.8 Unident. rodent 18 2.7 630.0 6.3 Mammal subtotal 231 34.5 6638.0 65.9

Birds Cyanocittacristata 5 0.7 435.0 4.3 Sialia sialis 2 0.3 64.0 0.6 Turdusmigratorius 1 0.1 77.0 0.8 Unident. warbler 1 0.1 10.0 0.1 Quiscalusquiscula 2 0.3 228.0 2.3 Cardinalis cardinalis 6 0.9 264.0 2.6 Pipilo erythrophthalmus 3 0.4 123.0 1.2 Unident. passerine 17 2.5 680.0 6.8 Unident. bird 2 0.3 112.0 1.1 Bird subtotal 39 5.8 1993.0 19.8 Amphibians Unident. salamander 1 0.1 3.5 < 0.1 Rana spp. 1 0.1 30.0 0.3 Fish Notropischrysocephalus 9 1.3 117.0 1.2 Amphibian/fish subtotal 11 1.6 150.5 1.5 Insects Acrididae 26 3.9 39.0 0.4 Tettigoniidae 2 0.3 3.0 <0.1 Unident. orthopteran 2 0.3 2.0 <0.1 Carabidae 30 4.5 6.0 < 0.1 Scarabaeidae 2 0.3 0.6 <0.1 Tenebrionidae 2 0.3 1.2 <0.1 Unident. coleopteran 123 18.3 36.9 0.4 Pentatomidae 2 0.3 0.4 <0.1 Apidae 3 0.4 1.2 <0.1 Noctuidae 2 0.3 2.0 < 0.1 Unident. insect 11 1.6 16.5 0.2 ,JUNE 1992 SCREECH-OWLPREY USE 69

Table 1. Continued.

OCCURRENCE BIOMASS

PREY N % GRAMS

Crustaceans Astacidae Cambarusspp. 10 1.5 65.0 0.6 Unident. crayfish 172 25.6 1118.0 11.1 Arachnids Unident. spider i 0.1 0.5 < 0.1 Gastropods Polygridae 2 0.3 0.8 < 0.1 Invertebrate subtotal 390 58.1 1293.1 12.8

Overall total 671 100.0 10 074.6 100.0

Table 2. Summary of prey use by Eastern Screech-Owls.

PERCENT OCCURRENCE PERCENT BIOMASS

FISH, FISH, AMPHIB- AMPHIB- IANS, IANS, AND AND MAM- IN- REP- MAM- IN- REP- PREY LOGATIONa PERIODb MALS BIRDS VERTS. TILES MALS BIRDS VERTS.c TILES ITEMS METHOD d

Michigan-1 NB 91.9 7.7 0.4 0 89.8 10.2 * 0 235 P Michigan-1 B 46.2 16.9 36.9 0 62.2 29.9 7.9 0 65 P Michigan-2 Sept.-May 99.3 0.3 0.4 0 99.5 0.4 0.1 0 1549 P Wisconsin all 68.6 26.3 2.2 2.9 71.6 18.0 0.4 10.0 137 P New York B 6.1 36.1 48.4 9.4 27.1 45.0 7.9 20.0 213 C, P, O Ohio B 30.4 64.8 0.8 4.0 27.1 59.8 0.1 13.0 477 C Ohio NB 60.3 26.5 2.5 10.7 50.5 29.3 0.3 19.8 121 C Illinois NB 92.2 7.8 0 0 89.6 10.4 0 0 128 P Missouri all 92.4 7.0 0.4 0.2 92.1 7.7 * 0.2 497 P Kentucky-1 all 14.7 14.8 70.5 0 39.1 56.4 4.5 0 244 S, P Kentucky-2 B 29.0 5.6 63.5 1.9 61.6 21.0 15.5 1.9 203 P, C Kentucky-2 NB 49.3 5.9 43.8 1.0 75.5 16.1 7.7 0.7 468 P, C Tennessee B 16.5 63.7 9.9 9.9 10.8 68.2 0.6 20.4 91 C Tennessee NB 4.2 72.9 6.2 16.7 1.9 65.1 0.5 32.5 48 C Tennessee all 4.7 1.2 93.1 1.0 49.8 15.2 18.7 16.3 407 S Arkansas all 8.8 8.8 76.5 5.9 18.5 57.3 12.4 11.8 34 S

Overall 60.9 14.4 22.9 1.8 73.7 19.5 1.7 5.1 4917 a References= Michigan-l, Craigheadand Craighead1956; Michigan-2, Wilson 1938; Wisconsin,Errington 1932; New York, Allen 1924; Ohio, VanCamp and Henny 1975; Illinois, Cahn and Kemp 1930; Missouri,Korschgen and Stuart 1972; Kentucky-I, Brown 1989; Kentucky-2,this study;Tennessee, Duley 1979;Arkansas, Hanebrink et al. 1979. bNB = non-breedingperiod, B = breedingperiod, and all = all year. ½* = less than 0.1%. d C: cachedprey, P = pellets,O = directobservation, S = stomachcontents. 70 GARY RITCHISON AND PAUL M. CAVANAGH VOL. 26, No. 2

OCCURRENCE BIOMASS

5O z 4O

2O

10

MAMMALS BDS !VERT. OTHER

PREY

Figure 1. Prey use (N = 735) by EasternScreech-Owls during the non-breedingperiod usingdata derivedfrom several studies. zidae (47.3% of passerines),Muscicapidae (12.1% seasonal variation in the diet of screech-owls in the of passerines)and Passeridae(9.6% of passerines). northeastern United States and Ontario, Canada, The most commoninvertebrate prey were crayfish using stomachcontent data. Analysis revealedthat (24%), mothsand butterflies(26.6%), beetles(23.8%), 61% of the screech-owlstomachs collected during and cricketsand grasshoppers(15.3%). April through November containedarthropod (pri- Severalinvestigators have reported seasonal vari- marily insect)remains while only 18% of the stom- ation in prey use by screech-owls(Table 2). Craig- achscollected during Decemberthrough March con- head and Craighead (1956) found that screech-owls tained arthropod remains. in Michigan used mammalian prey almost exclu- For all studiesproviding seasonaldata combined sivelyduring the non-breedingperiod but used a (Allen 1924, Cahn and Kemp 1930, Craigheadand variety of prey (mammals,birds, and invertebrates) Craighead1956, VanCamp and Henny 1975, Duley during the breedingperiod (Table 2). On the basis 1979, this study), the mostcommon prey (both in of cachedprey, VanCamp and Henny (1975) found frequencyof occurrenceand biomass)during the that small mammalswere the mostcommon prey of non-breedingperiod were mammals (Fig. 1) while screech-owlsduring the non-breedingperiod (Oc- the most commonprey during the breedingperiod tober-February) while birdswere the mostcommon were birds (Fig. 2). Invertebrateswere preyedupon prey duringthe breedingperiod (March-June; Ta- more frequently during the breedingperiod (33.3% ble 2). VanCamp and Henny (1975) alsoexamined of all prey; Fig. 2) than during the non-breeding JUNE 1992 SCREECH-OWLPREY USE 71

•0 m OCCURRENCE 0 I BIOMASS

MAMMALS BRDS VERT, OTHER

PREY

F•gure 2. Prey use (N = 1314) by EasternScreech-Owls during the breedingperiod.

period(Fig. 1), but only accountedfor 4.4% of total study).Other differencesbetween locations were also prey biomass(Fig. 2). apparent. For example, few invertebrateswere used Prey useby screech-owlsvaried with location(Ta- by screech-owlsin Missouri (Korschgenand Stuart ble 2), however,differences in methodologyand the 1972) while many were used by screech-owlsin time and durationof studieswere probably respon- central Kentucky (this study;Table 2). siblefor someof thisvariation. Among studies using The meanmass of all prey (N = 4917) takenby similarmethods (examining pellets and cached prey) screech-owlswas 28.29 + 0.33 (SE) g. During the and timing (all or mostof the year), mammalswere non-breedingperiod, the mean massof screech-owl predominantat both northern (Wisconsin,Erring- prey (N = 735) was 31.77 + 0.88 g. During the ton 1932; Michigan, Craigheadand Craighead1956; breedingperiod, the mean massof prey (N = 1314) Ohio, VanCamp and Henny 1975) and more south- takenby screech-owlswas 24.61 + 0.90 g. The mean ern (Missouri, Korschgenand Stuart 1972; Ten- massof prey itemsin eachof the major prey groups nessee,Duley 1979; Kentucky,this study)locations was 34.27 + 0.26 g for mammals(N = 2992), 38.23 (Table 2). Thesestudies also suggest that birdswere + 1.02 g for birds (N = 708), 31.50 + 6.93 g for used more frequently by screech-owlsat northern amphibians(N-- 34), 106.34 + 7.81 g for fish (N locationsand invertebratesmore frequentlyfurther = 56), and 2.12 + 0.05 g for invertebrates(N = south.However, theseresults were due largely to 1126). The mean massfor fish is relatively high just two studies(VanCamp and Henny 1975, this becausesix of nine speciesreported as prey are po- 72 GARY RITCHISON AND PAUL M. CAVANAGH VOL. 26, NO. 2 tentially larger than screech-owlsand, therefore,were nest boxes,while Allen (1924) used cachedprey, assigneda massof 150 g. pellets,and direct observations.Screech-owls rarely cachesmall prey itemslike invertebrates(VanCamp DISCUSSION and Henny 1975), explainingthe apparentnear ab- Prey useby EasternScreech-Owls may vary with sence of invertebrates in the diet of screech-owls in season and location, but our results indicate that northern Ohio. Similarly, Duley (1979) reported small mammals and birds contribute the most bio- few invertebrates(less than 10% of all prey items) mass. Invertebrates were sometimes taken more fre- in the diet of screech-owlswhen examiningcached quentlythan otherprey (e.g.,Alien 1924, VanCamp prey but foundmany invertebrates(more than 90%) and Henny 1975, Duley 1979, Brown 1989, this when using stomachcontent analysis (Table 2). study),however, the small sizeof mostinvertebrates Some differencesin prey use betweenlocations limited their contributionto total prey biomass. may be due to differencesin prey availability. For Invertebrates were taken more frequently by example, although screech-owlsrarely preyed on screech-owlsduring the breedingperiod than during crayfish at other locations(see referencesin Table the non-breedingperiod (Craigheadand Craighead 2), we foundthat crayfishwere frequentlyused by 1956, VanCamp and Henny 1975, Duley 1979, this screech-owlsin central Kentucky. Our study site is study). Increaseduse of invertebratesby screech- a low, poorly drained area (seeBelthaff 1987 for a owls during the breedingperiod may be due to in- descriptionof the area) supportinglarge numbers creased availability at this time. Screech-owlsat of terrestrial crayfish (Cambarusspp.) (pers. obser- northern locationsalso took birds more frequently vation). during the breedingperiod (e.g.,Allen 1924, Craig- Our overall estimateof the mean massof prey head and Craighead 1956, VanCamp and Henny usedby EasternScreech-Owls was 28.3 g, and mean 1975). No seasonalvariation in the number of birds prey masswas lower for the breedingperiod than in the diet of screech-owls was found in either Ken- for the non-breedingperiod. Based on previousstud- tucky (this study) or Tennessee(Duley 1979). In- ies of screech-owlfood habits, Marti and Hague creased use of birds by screech-owlsduring the (1979) estimateda mean prey massof 38.1 g. Dif- breedingperiod at northernlocations may be due to ferencesin estimatesof the massof prey itemsmay the increasedavailability of birds plus the reduced have contributed to this difference. In addition, how- availabilityof otherprey. Craigheadand Craighead ever, we used data from more recent studies con- (1956:289) reportedthat "meadowmice and all oth- ductedin the southernUnited States(Duley 1979, er prey species,with the exceptionof the small-bird Hanebrink et al. 1979, this study). These studies group,reached a periodof minimum populationden- revealedgreater use of smaller prey (invertebrates) sity in spring" in Michigan. VanCamp and Henny by screech-owlsthan previousstudies and, as a re- (1975:18) suggestedthat the breeding period of sult, our overall estimateof mean prey masswas screech-owls in northern Ohio was "timed to take lower. Similarly, our estimateof mean prey mass advantageof the spring migration of small birds." was lower during the breedingperiod than the non- Prey availability may fluctuateless at more southern breedingperiod becauseof an increaseduse of in- locations,with ectothermsmore likely to be available vertebrates. throughoutthe year. Thus, screech-owlsfurther south Although capable of killing prey with masses (e.g., Kentucky and Tennessee)may not be as de- greater than 100 g, our resultsindicate that Eastern pendent on the influx of small birds that occurs Screech-Owlstypically use much smaller prey. Sim- during spring migration. ilarly, Marti and Hague (1979) found that captive Differencesin methodologywere responsiblefor screech-owlsoffered lab miceof varioussizes usually someof the variation reportedin prey useby screech- selectedsmaller prey over larger. There are several owls. For example, birds were the most frequent reasonswhy screech-owlsmay selectsmaller prey: prey of screech-owlsduring the breedingperiod in 1) more small prey speciesare available,2) smaller northern Ohio (VanCamp and Henny 1975) while prey are likely younger and more vulnerable, 3) invertebrateswere the mostfrequent prey of screech- capturing larger prey may require greater energy owls during the breedingperiod in New York (Allen expenditureif suchprey escapemore often, 4) risk 1924). However, VanCamp and Henny (1975) de- of injury may be greater with larger prey, and 5) scribedfood habits basedsolely on prey cachedin sit-and-wait predatarslike screech-owlsexpend lit- JUNE1992 SCREECH-OWLPREY USE 73 tle energyin searchingand may be able to afford to age,and sex.Bull. No. 5 CarnegieMuseum of Natural take smaller,easier prey (Marti and Hogue 1979). History. Our results indicate that Eastern Screech-Owls CRAIGHEAD,J.J. AND F.C. CRAIGHEAD. 1956. Hawks, usea wide variety of prey, with vertebratespredom- owls, and wildlife. StackpoleCo., Harrisburg, PA. inant in terms of biomass, and, furthermore, that DULE¾, L.J. 1979. Life history aspectsof the screech owl (Otusasio) in Tennessee.M.S. thesis,University prey usevaries with time of year. Theseconclusions, of Tennessee, Knoxville, TN. however,are basedlargely on studiesconducted at DUNNING, J.B., JR. 1984. Body weights of 686 species northern locations,many of which focusedon prey of North American birds. Monograph No. 1, Western useby screech-owlsduring the non-breedingperiod, Bird Banding Association. Eldon Publishing, Cave when owls roost in natural or artificial boxes and Creek, AZ. prey remainsare easierto locate.In addition, tech- ERRINGTON, P.L. 1932. Food habits of southern Wis- niques used to examine prey use by screech-owls consinraptors. Part I. Owls. Condor34:176-186. may overemphasizethe importanceof certain types HANEBRINK, E.L., A.F. POSEYAND K. SUTTON. 1979. of prey. Studiesof prey useby screech-owlsrelying A note on the food habits of selected raptors from northeastern Arkansas. Arkansas Acad. Sci. Proc. 33: more on either stomachcontent analysis or direct 79-80. observationand conductedduring the breedingpe- HENNY, C.J. AND L. VANCAMP. 1979. Annual weight riod and in the southern part of their range may cyclein wild screechowls. Auk 96:795-796. yield different results. JOHNSGARD,P.A. 1988. North American owls: biology ACKNOWLEDGMENTS and natural history. SmithsonianInstitution Press, Washington, DC. We thank Corrine Wells for helping with the identi- ficationof prey and James R. Belthoff for assistancein KELLNER, C.J. AND G. RITCHISON. 1985. An exami- collectingpellets. Carl Marti, Brian Millsap and Denver nation of the predatory behavior of captive American Holt providedmany useful commentson the manuscript. Kestrels. Trans. KentuckyAcad. Sci. 46:137-140. This studywas supportedby fundsfrom EasternKentucky KORSCHGEN,L.J. ANDH.B. STUART. 1972. Twenty years University. of avian predator-smallmammal relationshipsin Mis- souri.J. Wildl. Manage. 36:269-282. LITERATURE CITED MARTI, C.D. 1974. Feeding ecologyof four sympatric ALLEN,A.A. 1924. A contributionto the life historyand owls. Condor 76:45-61. economicstatus of the screechowl (Otusasio). Auk 41: 1987. Raptor food habits studies.Pages 67-80 1-16. in B.A. Giron Pendleton,B.A. Millsap, K.W. Cline BARBOUR,R.W. AND W.H. DAVIS. 1974. Mammals of and D.M. Bird [EDS.],Raptor managementtechniques Kentucky.University Pressof Kentucky,Lexington, manual. National Wildlife Federation, Washington, KY. DC. BELTHOFF,J.R. 1987. Post-fledgingbehavior of the -- AND J.G. HOGUE. 1979. Selectionof prey by EasternScreech-Owl. M.S. thesis,Eastern Kentucky size in screech owls. Auk 96:319-327. University, Richmond, KY. STEENHOF,K. 1983. Prey weightsfor computingpercent BROWN,R.K. 1989. Foodhabits of Kentuckyowls. Ken- biomassin raptor diets. Raptor Res. 17:15-27. tucky Warbler 65:38-48. TRAUTMAN, M.B. 1981. The fishes of Ohio. Ohio State BURT, W.H. AND R.P. GROSSENHEIDER. 1964. A field University Press,Columbus, OH. guideto the mammals.Houghton Mifflin Co., Boston, VANCAMP,L.F. AND C.J. HENNY. 1975. The screech MA. owl: its life historyand populationecology in northern CAHN,A.R. ANDJ.T. KEMP. 1930. On the foodof certain Ohio. North American Fauna No. 71, Fish and Wild- owls in east-central Illinois. Auk 47:323-328. life Service,U.S. Department of the Interior. CARLANDER, K.D. 1969. Handbook of freshwater fish- WILSON, K.A. 1938. Owl studies at Ann Arbor, Mich- ery biology.Iowa StateUniversity Press, Ames, IA. igan. Auk 55:187-197. CLENCH,M.H. ANDR.C. LEBERMAN.1978. Weightsof 151 speciesof Pennsylvaniabirds analyzed by month, Received2 January 1992; accepted24 March 1992