Barred Owl and Spotted Owl Populations and Habitat in the Central Cascade Range of Washington

j RaptorRes. 34(4):279-286 ¸ 2000 The Raptor ResearchFoundation, Inc.

BARRED OWL AND SPOTTED OWL POPULATIONS AND HABITAT IN THE CENTRAL CASCADE RANGE OF WASHINGTON

DAL• R. HERTER RaedekeAssociates 5nc., 5711 N.E. 63rd Street,Seattle, WA 98115 U.S.A.

LORIN L. H•cIcs Plum Creek Timber Co., L.P., 999 3rd Avenue, Suite 2300, Seattle, WA 98102 U.S.A.

A•$TRACT.--The Barred Owl (Strix varia) has continued to expand its range southwardinto the north- western United States from Canada since the 1970s, and has become an established member of the forest avifaunain westernWashington. There is increasingconcern that it may be competingfor re- sourceswith the threatened Northern Spotted Owl (S. occidentaliscaurina) throughout its range. We surveyedfor SpottedOwls over an extensivearea of the central CascadeRange of Washingtonduring the breeding seasonsof 1991-93. Both Spotted Owls and Barred Owls respondedto tape recordings and vocalimitations of SpottedOwl calls.By usingpair responsesor grouping singleowl responsesfrom closegeographic locations on at least three different surveynights, site centersrepresenting probable breeding pairs or territorial single individualswere designatedfor both species.A total of 53 Barred Owl and 62 Spotted Owl site centerswere identified in the 1280 km9 surveyarea. Barred Owls were found at greatestdensities on the wetter,western portions of the CascadeRange. On the driest, eastern portionsof thismountain range,Barred Owlswere usuallyfound alongmajor river and streamcorridors, in the vicinity of forested wetlands,or at higher elevationsreceiving increasedprecipitation. We com- pared the extent of mature, young, and other forest habitats at radii of 0.8 and 1.6 km around site centers of both species.Spotted Owls used siteswith greater amounts of mature coniferousforest than did Barred Owls within 0.8 km of site centers acrossall portions of the study area. Additionally, we found no evidenceof mixed-speciespairing or hybridsof the two speciesduring the study,suggesting that extensivehybridization may not be occurring where Barred Owls have become firmly established within the range of the Spotted Owl.

K•¾ WORDS: BarredOwl; Strix varia; NorthernSpotted Owl; Strix occidentalis;interbreeding;, populations; habitat;,Washington.

Poblacionesy habitat de Strixvaria y Strixoccidentalis en el central Cascadede Washington RES•MEN.--St•ixvaria ha continuado expandiendo su rango hacia el sur dentro del noroeste de los EstadosUnidos desde Canada a parfir de 1970. Alli se ha establecidocomo miembro de la avifauna de bosque en el oeste de Washington. Existe una creciente preocupaci6n de que pueda estar com- pitiendo pot recursoscon el amenazado Strix occidentaliscaurina a lo largo de su rango. Examinamos una vasta area en busqueda de Strix occidentalisen la regi6n del Central Cascade de Washington durante las estacionesreproductivas de 1991-93. Ambos buhos respondieron alas grabaciones e imitaci6n de vocalizacionesde Strix occidentalis.Mediante la utilizaci6n de respuestaspareadas o la agrupaci6n de respuestasfinicas de localidades geogrfificascercanas en al menos tres noches di- ferentes de investigaci6n, fueron encontrados los sitios centrales los cuales probablemente repre- senraton a parejas en reproducci6n o a individuos territoriales de las dos especies.Un total de 53 sitios centrales de Strix varia y 62 sitios centrales de Strix occidentalisfueron identificados en los 1280 kineinvestigados. Strix varia fue usualmenteencontrado a lo largo de los rios y quebradas,en la vecindad de humedales boscososo a elevaciones mas altas con mayor precipitaci0n. Comparamos la extensi6n de bosquesmaduros y jovenes y otros tipos de habitat boscosoen un radio de 0.8 y 1.6 km alrededor de los sitios de centro de ambas especies.Strix occidentalisutiliz6 sitios con mayor cantidad de bosquesde coniferas maduros que Strix varia dentro de 0.8 km del sitio de centro a traves de todas las porciones del firea de estudio. Adicionalmente, no encontramos evidencia de especiesmezcladas en pareja o hibridos de las dos especiesdurante el estudio sugiriendo que la

279 280 HERTER AND HICKS VOL. 34, NO. 4

hibridacitn no est/t ocurriendo en los sitios en los cuales Strix varia se ha buen establecido dentro del rango de Strix occidentalis. [Traduccitn de C•sar M•trquez]

The Barred Owl (Strix varia) is a relatively recent We present the resultsof surveyefforts over a 3-yr member of the forest avifaunaof Washingtonstate. period, showing relative populations of Barred The specieswas first reported in the mid-1960sin Owls and SpottedOwls within the area of complete northeastern Washington. West of there, in the surveycoverage. We alsoinvestigated whether hab- northern WashingtonCascades, the first pair was itat conditionsaround territory centersfor the two recordedin 1974 (Taylorand Forsman1976). The speciesdiffered. We hypothesizedthat mature co- Barred Owl began to invade the range of the niferous forest habitat, known to be important to Northern Spotted Owl (S. occidentaliscaurina) in SpottedOwls, would be usedto a greater extent by southwesternBritish Columbia by the early 1970s this speciesthan by Barred Owls.

(Dunbar et al. 1991). Barred Owlshave apparently STUDY AREA AND METHODS become more numerous than Spotted Owls over a short period of time at the northern edge of the Following listing of the Northern Spotted Owl as a Threatened Speciesin July 1990, extensivesurvey pro- Northern Spotted Owl's range. From 1985-88, for grams were initiated to provide site-specificdata for the example, extensivesurveys in southwesternBritish reviewof timber harvestapplications in SpottedOwl hab- Columbia found 57 Barred Owl territories and 14 itat. These surveyshelped to determine local abundance Spotted Owl territories (Dunbar et al. 1991). Sim- and distribution of Northern Spotted Owls, particularly in managed forests.We conducted surveysover an exten- ilarly, in 1985, Hamer (1988) found 15 Barred Owl siveand relativelycontiguous region of the centralWash- territories and 8 Spotted Owl territories in north- ington Cascadesin an area of checkerboard land own- western Washington. By the 1990s, Barred Owls ership. The area is typified by alternating sections(1 6 had expanded their range through Oregon and km2) of public and privateownership. Public lands are administered by the U.S. Forest Service (USFS) and, to become established in northern California in the a lesserextent, by the WashingtonDepartment of Natural southern reaches of the Northern Spotted OwI's Resources (DNR). Surveyswere inclusive of all owner- range (Dark et al. 1998). shipswithin the surveyboundaries. Both Barred Owls and Spotted Owls are similar The area of surveycoverage straddled the crest of the CascadeMountains in central Washington, extending in size, select mature forest habitats (Gutifirrez et acrossboth the east and west slopesof the range (Fig. al. 1995, Haney 1997, Mazur et al. 1997), and ap- 1). This area includedmajor portionsof the upper Green pear to have some overlap in prey use (Devereaux and Yakima Riversand their tributaries, and minor por- and Mosher 1984, Gutifirrez et al. 1995). Possible tions of the upper White and Naches River basins.To- pography consistedof steep,mountainous terrain deeply competition betweenthe two speciesmay favor the bisected by rivers and streams.Elevations ranged from slightlylarger and possiblymore aggressiveBarred 400-2000 m and weatherranged from rainy,mild winters Owl (Sharp 1989, Hamer et al. 1994, Dark et al. with cool summerswest of the crestto snowy,cold winters 1998). The Interagency Scientific Committee to with warm summerseast of the crest. The study area was predominantly composed of coniferous forest habitats Addressthe Conservationof the Northern Spotted ranging from early to late successional,with a history of Owl (Thomas et al. 1990) noted that potential timber harvestand fire disturbanceon both private and competitionwith the Barred Owl wasof immediate federal lands. Minor portions of the studyarea were cov- concern in maintaining viable Spotted Owl popu- ered by deciduousor mixed forests(primarily in major river valleys),shrub, herb, and grass-dominatedhabitats, lations in the northern Cascadesof Washington or bare rock and talus. (north of Mount Rainier). Considering the rapid The rain-shadoweffect of the CascadeRange produces spread of this congener acrossthe range of the a gradient of fbrest types from west to east, with mmst Northern Spotted Owl, understandingthe habitat conifer forestsoccurring west of the crest,and extending east of the crest for variable distancesdepending on el- relationshipsof the two speciesin areaswhere they evation (higher elevationsreceived more precipitation), are now sympatric is important for future conser- this type is graduallyreplaced by dry conifer forestssev- vation planning for this threatened owl. eral kilometerseast of the crest.We surveyedfor owlsm During extensive surveysfor Spotted Owls, we nearly all forested habitats up to 1525 m in elevation Near this elevation, west of the Gascade crest, low-eleva- noted that Barred Owls responded regularly to tion forestsdominated by Douglas-fir(Pseudotsuga menz•e- broadcastsof tape recordingsand vocal imitations sii) and westernhemlock ( Tsugaheterophylla) are replaced of Spotted Owl calls (see also Dunbar et al. 1991). by stands of Pacific silver fir (Abiesamabilis), mountain DECEMBER 2000 BARRED AND SPOTTED OWL POPULATIONS IN CENTRAL WASHINGTON 281

•.•:-•-•1991 - 1993 Survey Areos ,.-, East oSpotted Owl Site m Borred Owl Site " ...IF?.- -•'":;"•=...... iiL,.';•""i...:,i•7: ' ,::!!'.;.;i,.:,•.,,.,..:%;jL,.,.j!L East- ! sop I eth Areo ......

I '"=' ...... =.' --- County Boundory

• s T.O.•*•.--I•.J[KILOMETERS

KINO CO.

KITTITAS CO.

P l ERCE CO.

Figure 1. Location of the surveyedarea in central Washingtonshowing distribution of Barred Owl and SpottedOwl site centers.The three major subdivisionsof the study area based on geography (Cascadecrest) and rainfall (150 cm annual isopleth) are also shown. hemlock (T. mertensiana),and noble fir (A. procera)at surveyseason approximated the breeding seasonfor Strix higher elevations. Similarly, low-elevation forests domi- owls in the local area. Surveysfor Spotted Owls followed nated by Douglasfir, grand fir (A. grandis),and Ponde- U.S. Fish and Wildlife Service(1991, 1992) guidelinesfor rosa pine (Pinus ponderosa)in the eastern Cascadesare surveying lands proposed for forest management activi- replaced by standsof Pacific silver fir, subalpine fir (A. ties. Individual surveyareas were establishedaround pro- lasiocarpa),mid Engelmann spruce (Piceaengelmanni•3 at posed timber harvest units, extending 2.9 km in radius higher elevations.Spotted Owls were not thought to nest from the perimeter of each unit (harvest units were 5- aboveapproximately 1525 m in the WashingtonCascades 35 ha in size). These bounds were selected because a (see Allen et al. 1989). circle of radius 2.9 km (26.4 km• approximated the av- We conducted Spotted Owl surveysfrom 1991-93, sur- erage size of a Spotted Owl territory based on regional veying between 15 March-31 August in each year. The home range studies (WSFPB 1996). Survey areas often 282 HERTER AND H•C• VOL. 34, NO. 4 overlapped, yielding several large regions of complete site than late seasonresponses, although pair responses coveragewith rounded perimeters (Fig. 1). alwaystook priority over single responses. In each surveyarea, calling stationswere established We overlaid isoplethsof annual precipitation on study along roads, trails, or on off-trail routes to provide com- area maps to compare the effects of the east-westmois- plete audio coverageof all potential habitat of Spotted ture gradient acrossthe Cascadeson owl distribution.We Owls. Calling stationswere typically 0.4-0.8 km apart also plotted site centers on habitat maps digitized from along roads or trails, with closer spacingin off-trail areas. 1:64 000 aerial photography. We used mapping that was Surveysconsisted of an observerconducting a 10-minvis- originally prepared for Spotted Owl management plan- it to each calling station, repeated six times over a survey ning based on Washington DNR habitat definitions in season,or three times in each of two consecutivesurvey use at the tiine, and separated all habitats into three seasons. All road and most trail stations were visited dur- types: (1) Old Forest Habitat which was dominated by ing hours of darkness,and for safetyreasons, some trail coniferoustrees typicallyover 100 yr old, >60% canopy and all off-trail stationswere visited during the day, usu- cover, one to multiple canopylayers, and at least 40% ally during afternoon or early evening hours when we cover of Douglas-fir;(2) Young ForestHabitat which was suspectedowls to be more responsive.During each 10- dominated by trees typically<100 yr old (but of sufficient rain calling session,observers imitated calls of Spotted height and spacing to allow movemerit of owls during Owlsvocally, broadcast a playbackof severaltypes of Spot- foraging), >60% canopycover, and typicallya singlecan- ted Owl calls, or used both methods to elicit responses opy layer; (3) Non-habitatwhich wasmade up of forested from owls.Calling wasinterspersed with periods of listen- habitats with overstory trees <10 m in height, standswith <60% canopycover and/or <40% coverof Douglas-fir, ing at the observer'sdiscretion, with generally 3-4 min deciduous stands or mixed stands with >25% deciduous of callsand •-7 min of listeningat each station.Calling overstory,and all forests>1525 m elevation.Shrub, herb was often concentrated at the beginning of the 10-min and grass-dominatedhabitats, bare rock arid talusslopes, period, and listening concentrated during the latter half farmland, and water were also included in the Non-hab- of the 10-min period. Responsesfrom all large owl spe- itat category. cieswere mapped and information on species,sex, move- To compare habitatsnear site centersof both species, ments, and other observationswere recorded. All Spot- we drew concentric circles of 0.8- and 1.6-km radius ted Owl responseswere investigatedthe fbllowing day or around each site center. Circular areas around Spotted as soon as possibleto determine reproductivestatus. Owl siteshave been used in similar investigationsof hab- Maps containing Spotted Owl and/or Barred Owl re- itat patterns (Lehmkuhl and Raphael 1993, Meyer et al sponsesfrom the six surveyvisits were reviewedfollowing 1998, Swindle et al. 1999). Habitat comparisonsin our the third and final surveyseason. Sites where we obtained studywere restricted to mature and young coniferousfor- at least one responsefrom a pair of owls, or at least three est habitats becauseof the demonstratedimportance of responseson three differentnights (separatedby >7 d) mature foreststo Spotted Owls (Thomas et al. 1990) and from singleowls of either sexwithin a 0.2-km radiusarea, the suggestionthat Barred Owls could usestands of youn- were designatedas site centersfor that species.If an ac- ger forest (Hamer 1988). tual nest tree was located, this location then became the We followed recent habitat studies of Spotted Owls site center. The techniqueswe usedto designatesite cen- (Meyer et al. 1998, Swindle et al. 1999) in selecting the ters for both owl specieswere essentiallyidentical to pro- two circular areas for determining the nest-sitelocations cedures used to determine regulatory Spotted Owl site of Spotted Owls. Radii of --•0.8 km have been shown to centers by state and federal agencies.Each site center is have significant differencesin comparisonsof habitat consideredlikely to represent a territorial individual or around nest sites and random fbrest sites (Meyer et al. pair (U.S. Fish arid Wildlife Service 1992). Previously- 1998, Swindle et al. 1999), and differences in the amount known Spotted Owl site centerswhich were not occupied of old fbrest may occur up to 1.6 km (Swindle et al. during our three surveyyears were not included in the 1999). We stratified owl sites in our area into three sub- sample.Although we did not follow-upon night respons- units basedprimarily on precipitation criteria: westof the es to determine nest sites for Barred Owls, designation CascadeRange crest, east of the crest to the 150 cm pre- of site centers was usually apparent based on clustersof cipitation isopleth, arid east of the 150 cm isopleth. Our responsesand consistencyof responselocations in mul- comparisonsof average amounts of each habitat type tiple years. We provided six opportunities for territorial within the tested radii were achievedusing multiple anal- owlsto respond to our callsand often over three respons- ysisof variance (MANOVA), following testsfor normality es were used to determine a site center. In addition, the and use of the Wilks' lambda (likelihood ratio criterion) mountainous terrain helped delimit responses,which to test for significant interaction betweenvariables (SYS- were often located in distinct valleysand separated from TAT version 8.0). We randomly sampled circular areas a nearby site center by an obviousridge (thereby out of around site centers, and used mutually exclusive (site hearing range of the other pair). Simultaneousor near- centers of both speciestested at 0.8-kin radius were not simultaneous calls from adjacent pairs or singles of the used for testsat 1.6-km radius), nonoverlapping areasfor same sex on a given night also helped delimit one site both radii. from the next for each species. The actual center was placed on the earliest record of a pair (or nest for Spot- RESULTS ted Owls) during a season,and likewise the earliest record of a single if no pair was ever found. Early season Population Size and Distribution. Spotted Owl responseswere assumedto be closer to a potential nest surveys,when combined over three breeding sea- DECEMBER 2000 BARRED AND SPOTTED OWL POPULATIONS IN CENTRAL WASHINGTON 283 sons,covered 1280 km2. Portions of the surveyed forest than Spotted Owl sites in the far west and area above 1525 m, or extensive areas classified as far east subunits. nonhabitatwere not surveyed.We may have missed In the dry zone of the eastern Cascadeseast of some Barred Owls by not surveying in forested the 150-cm isopleth, 8 of 12 Barred Owl site cen- habitatscontaining >75% deciduoustrees. Large ters were found in moister forest situations, such standsof mixed and deciduous forests comprised as those along major river or stream drainages or <2% of the studyarea and occurred only in the near lakes or wooded swamps or at higher eleva- floodplain of the Green and Yakima Rivers. Like- tions where the true amount of precipitation may wise,stands of <60% canopyclosure were uncom- actually have exceeded 150 cm/yr. On both slopes mon and small in size,and often occurred adjacent of the CascadeRange, severalBarred Owl sitesoc- to surveyedstands, therefore receivinglimited sur- curred in deciduous and mixed forest stands found vey coverage (Fig. 1). exclusively in major river valleys. Forest stands A total of 62 Spotted Owl site centers and 53 dominated by deciduoustrees are not considered Barred Owl site centers were identified. Spotted important Spotted Owl habitat in Washington Owls were well-distributed across the area (0.047, (WSFPB 1996). East of the 150-cm isopleth, Spot- 0.043, and 0.053/km 2 from westto eastby subunit; ted Owl siteswere typically located in coniferous Fig. 1). Barred Owls were most abundant west of forests on the sidesof slopesand were not found the Cascade crest (0.063/km2), with similar densi- in the habitats described above for Barred Owls. ties (0.063/km2) extendingeast of the crestonly West of the 150-cm isopleth and above major river within the 150 cm/yr isopleth for annual precipi- valleys,however, Spotted Owl sitesoccurred in very tation. East of this line, Barred Owl densities similar situations to those of Barred Owls. We did dropped to 0.019/km •. To the westof our survey not find Spotted Owl nestsin high-elevation,true area within the CascadeRange, only Barred Owls fir-dominated forests. Our own observations of were located during similar surveysfrom 1991-93 Barred Owls, plus those of Wright and Hayward (L. Young pers. comm.). To the east of our study (1998), suggestthat this speciesis also more com- area, severaladditional Spotted Owl sitesand a few mon in lower elevation mixed conifer forests than Barred Owl sites have been located across north- in high elevation spruce-fir forests. ern Kittitas County almost to the forest/sagebrush DISCUSSION steppe interface (S. Sovern and M. Taylor pers. comm.). Also, we have found Barred Owls breed- Population Size and Distribution. The full im- ing at sitesboth lower and higher in elevation than pact of the Barred Owl range expansion into the known Spotted Owl nest locations. Barred Owls Pacific Northwest on resident Spotted Owls prob- have completelyoverlapped the known geographic ably hasyet to be fully realized.We detectedalmost and altitudinal distribution of SpottedOwls in cen- as many Barred Owls as Spotted Owls, and in some tral Washington. portions of the WashingtonCascades, Barred Owls Habitat Analyses.We found no significant differ- have become more numerous than Spotted Owls. ences in the mean amount of all habitat types be- We could have missed some territories of both owl tween Spotted and Barred Owls within the 1.6 km species,particularly Barred Owls; however,we re- radius analysisarea (Wilks' It = 0.946, P = 0.475) ceived consistentresponses from both speciesat around site centers. Within the 0.8 km radius sur- night and during the day, even though we only rounding Spotted Owl and Barred Owl sites,how- broadcast Spotted Owl calls. Responsesobtained ever, significant differences in mean habitat during the day were typically at closer range than amounts were detected (Wilks' It = 0.725, P = at night. Daytime surveyswere designedwith closer 0.003). Spotted Owl sitescontained more old for- spacingof calling stationsand transectsto account est close to the site center than Barred Owl sites. for this tendency. Even so, we could have missed Within the three geographic regions we tested, some owls,particularly Barred Owls, becauseof in- MANOVA results indicated that mean amount of dividual variation in response levels to calls of a habitat differed significantly within the 0.8 km congener. (Wilks' It = 0.594, P = 0.001) radius. There was All Spotted Owl sitesknown in the survey area consistentlymore old forest surrounding Spotted were monitored for occupancy and reproduction Owl sites than Barred Owl sites in all subunits (Ta- annually from 1991-98. Of the 62 known sites,22 ble 1). Barred Owl sitesalso contained more young were unoccupied at least temporarily by both 284 HERTER AND HICKS VOL. 34, NO. 4

Table 1. Comparison of mean hectaresof habitat present within selectedradii around Barred Owl and Spotted Owl s•te centersacross three geographicregions in the Central Cascaderange of Washington.

WEST a E^ST a EAST 150 a RADIUS b (km) MEAN 95% CI N MEAN 95% CI N MEAN 95% CI N

0.8 km Old/Mature Forest Barred Owl 57 43 10 81 27 11 55 47 4 Spotted Owl 83 32 8 106 42 4 98 30 13 Young Forest Barred Owl 72 34 10 42 29 11 41 41 4 Spotted Owl 51 36 8 5 10 4 40 20 13 Non-habitat c Barred Owl 73 33 10 79 30 11 106 83 4 Spotted Owl 68 35 8 87 33 4 64 20 13

I 6km Old/Mature Forest Barred Owl 173 153 8 430 112 9 304 125 8 Spotted Owl 182 136 5 334 85 9 323 97 15 Young Forest Barred Owl 354 178 8 91 98 9 163 94 8 Spotted Owl 420 133 5 117 71 9 178 55 15 Non-habitat Barred Owl 403 161 8 442 144 9 545 200 8 Spotted Owl 405 42 5 456 156 9 489 103 15 aWest = west of the CascadeRange crest,East = east of the CascadeRange crest but west of the 150 cm/yr rainfall isopleth,East 150 = eastof the 150 cm/yr rainfall isopleth. •' Area within 0.8 km radius = 201 ha; 1.6 km radius = 804 ha. • Non-habitat included non-forest,deciduous-dominated forests, and high-elevationforests.

members of the original pairs. Of these 22 sites, 1991), but they persistat low densitiesand typically half remained unoccupied through 1998. Of the nest in a patch of old forest. In our study area, remaining 11 sites,six were reoccupied by differ- where relatively large stands(>200 ha) of old for- ent Spotted Owl pairs or single individuals, while est habitat remained, surrounded by a mosaic of Barred Owls were present at or near five site cen- managedand unmanaged fire-regeneratedhabitat, ters. In most cases,Barred Owls were already pre- both SpottedOwls and Barred Owlsoccupied nest- sent in the vicinity (--<0.8km) prior to the disap- ing territories and produced young. Our data sug- pearanceof the SpottedOwl pairs. In one instance, gestedthat Barred Owls persistedin areaswith less a newly establishedpair of Spotted Owls nested old forest than Spotted Owls. within I km (and hearing distance) of an estab- Within conservation areas designedfor Spotted lished Barred Owl site. Surveys over additional Owl habitat protection, management options that years are needed to determine whether Spotted consolidateand protect preferred habitat for Spot- Owls regularly reoccupysites in closeproximity to ted Owls in well-spaced,large blocks (>100 ha) Barred Owl territories. may help them compete with Barred Owls in Cas- Habitat Analyses. In portions of the western cade Range forests.Recent studiesby Meyer et al. WashingtonCascades west of our studyarea where (1998) and Swindle et al. (1999) have also noted less old forest remained, Barred Owls have occu- a preference for an unfragmented patch of old for- pied second-growthDouglas-fir/western hemlock est around Spotted Owl nest sites. This does not standswith remnant large trees and snagswhich mean that Barred Owls cannot successfullyoccupy provide nest cavities. Spotted owls have been areas of extensive cover of old forest. Observations known to occur in landscapeswhere young forests by Wright and Hayward (1998) and our own ob- predominate (Forsman et al. 1988, Irwin et al. servationsin neighboring wildernessareas and na- DECEMBER 2000 BARRED AND SPOTTED OWL POPULATIONS IN CENTRAL WASHINGTON 285 tional parks indicated that territorial Barred Owls petition in some habitats appears likely and may can occur in wildernessvalleys with extensivecover negativelyaffect Spotted Owl population recovery. of old forest. ACKNOWLEDGMENTS Some competition for resources likely takes place where the two speciesare sympatricbecause We are indebted to the many field biologistswho spent of significant overlap in habitat use, prey species, long nights surveyingfor owls and hiked many miles in steep terrain to provide complete surveycoverage; prom- and nest-sitepreferences. Spotted Owls and Barred inent among them were: L. Melampy,A. Stabins,M. Mac- Owls were previouslysympatric in only one other Donald, J. Bottelli, C. Smith, M. Rabanal, K. Jorgensen, area in North America, at the southern limit of the D. Malkin, H. Smith, S. Sagor,M. Lanphere, B. Shepard, ranges of both speciesin the southern Sierra Ma- C. Holloway, A. Raedeke, G. Riddick, M. Richey, and C. Eakins. R. Early deftly carried out the GIS analysisand B. dre Occidental of Mexico (Enriquez-Rochaet al. Marx, T. Hitzroth, and M. Baumgarmer produced the 1993, Howell and Webb 1995). In Mexico, there habitat maps. C. Olson, H. Stabins,and T. Hillman as- are two different subspeciesand the duration of sistedwith data analyses.We also thank S. Sovern and M the sympatryhas been longer. In our studyarea, Taylor of the U.S. Forest Service, Pacific Northwest Re- the northern subspeciesof both owlsappear to co- search Laboratory, for providing additional field survey coverageat owl sitesand reviewof the manuscript.Drafts exist in very similar habitats in the wet, western of the manuscript were also improved by the comments Cascades,but they may be exhibiting greater hab- of G. Hayward, H. Stabins,and two anonymousreviewers. itat separation in the eastern Cascades.In these LITERATURE CITED dryer forests,the predominanceof Spotted Owls in conifer forests at mid-slope (Buchanan et al. ALLEN, H.L., K.R. DIXON, •U'4DK.L. KNUTSON. 1989. Co- 1995), and Barred Owls in forested wetlands, operativeadministrative study to monitor SpottedOwl mixed riparian stands,and high elevationmoist co- management areas in national forestsin Washington niferous forests, mirrored the habitat use of the Unpubl. Rep., Washington Depart. Wildl., Olympia speciesover the majorityof their respectiveranges. WA, U.S.A. Spotted Owls, outside the coastalPacific North- BUCHANAN,J.B., L.L. IRWIN,AND E.L. MCCUTCHEN.1995. west, are primarily found in relatively-dry,western Within-standnest site selectionby SpottedOwls in the eastern Washington Cascades.J. Wildl. Manage. 59: mountains, while Barred Owls occur in more mesic 301-310. habitats in eastern mixed or deciduous forests and DARK,SJ., RJ. GUTIgRR•Z,AND G.I. GOULD,J[t. 1998. The boreal forests. Barred Owl (Styix va•a) invasion in California. Auh Barred Owlswere alreadywell-established on our 115:50-56. study area by the time we began our surveys.We DEWREAUX,J.G. ANDJ.A. MOSHE[t.1984. Breeding ecol- found no mixed-species (Barred Owl/Spotted ogy of the Barred Owl in the central Appalachians Owl) pairs or hybrid owls,but hybridshave been RaptorRes. 18:39-58. reported from Washingtonand other parts of the DUNBAR, D.L., B.P. BOOTH, E.D. FORSMAN,A.E. HETHER- Northern Spotted Owl range (Hamer et al. 1994). INCTON,AND DJ. WILSON.1991. Statusof the Spotted Owl, Strix occidentalis,and Barred Owl, Strix vmia, in Widespread hybridization in the central Washing- southwestern British Columbia. Can. Field-Nat. 105 ton Cascadesdid not appear to be continuing.As 464-468. shownin other species(Short 1969, Rohwer 1972), ENRiQUEZ-ROCI4_&P., J.L. P•GEL-SXI•ZPm, ^Nr) D.W it is likely that once Barred Owls establishedself- HOLT. 1993. Presence and distribution of Mexican sustaininglocal populations,individuals of the in- owls:a review.J. RaptorRes. 27:154-160. vadingspecies no longer had trouble finding con- FORSMA•,E.D. 1988. A surveyof Spotted Owls in young specific mates, minimizing the incidence of forestsin the northern CoastRange of Oregon. Mur- mixed-speciespairing. relet 69:65-68. Although this study suggestsonly minor differ- GUTIP.PO•Z, RJ., A.B. FRANKLIN,AND W.S. LAHAYE.1995 ences in the amount of old and mature forest hab- SpottedOwl (Styixoccidentalis). Pages 1-28 in A. Poole and E Gill lEDS.], The birds of North America, No. itat surroundingSpotted and Barred Owl site cen- 179. The Academyof Natural Sciences,Philadelphia, ters based on the broad seral stagesused in our PA and American Ornithologists' Union, Washington, analyses,perhaps more detailedhabitat use studies DC U.S.A. would indicate more partitioning. The extent that HAMER, T.E. 1988. Home range size of the Northern habitat or niche separation will keep the two spe- Barred Owl and Northern Spotted Owl in western cies from competing directly for resourcesshould Washington.M.S. thesis,W. Wash. Univ., Bellingham, be considered speculative.However, direct com- WA U.S.A. 286 HE}•q:E}•AND HICKS VOL. 34, NO. 4

, E.D. FORSMAN, A.D. FUCHS, AND M.L. WALTERS. SHORT,L.L. 1969. Taxonomic aspectsof avian hybridiza- 1994. Hybridization between Barred and Spotted tion. Auk 86:84-105. Owls. Auk 111:487-492. SWINDLE,K.A., W.J. RIPPLE,E.C. MESLOW,AND D. SCHAF- HANEy,J.C. 1997. Spatialincidence of Barred Owl (Strix ER. 1999. Old-forest distribution around Spotted Owl varia) reproduction in old-growth forest of the Ap- nests in the central CascadeMountains, Oregon. J. palachian Plateau.J. RaptorRes. 31:241-252. Wildl. Manage. 63:1212-1221. HOWELL, S.N.G. AND S.B. WEBB. 1995. The birds of Mex- T^V•OR,A.L., JR. ANt)E.D. FORSM^N.1976. Recent range ico and northern Central America. Oxford Univ. extensions of the Barred Owl in western North Amer- Press, New York, NY U.S.A. ica, includingthe first recordsfor Oregon. Condor78: IRWIN, L., T.L. FLEMING,S.M. SPEICH,ANDJ.B. BUCHANAN. 560-561. 1991. Spotted Owl presence in managed forests of THOMAS,J.W., E.D. FORSMAN,J.B. LINT, E.C. MESLOW, southwesternWashington. Tech. Bull. No. 601. Na- B.R. NOON, ANDJ. VERNER.1990. A conservationstrat- uonal Council of the Paper Industry for Air and egy for the Northern Spotted Owl. U.S. Fish Wildl. Stream Improvement, Inc., Corvallis, OR U.S.A. Serv. Portland, OR U.S.A. LEHMKUHL,J.F. ANDM.G. RAPHAEl..1993. Habitat pattern U.S. FISH AND WILDLIFE SERVICE. 1991. Protocol for sur- around Northern SpottedOwl locationson the Olym- veyingproposed management activities that mayim- pic Peninsula,Washington. J. Wildl.Manage. 57:302- pact Northern Spotted Owls. U.S. Fish Wildl. Serv., 315. Portland, OR U.S.A. MAZUR, K.M., P.C. J^MES,MJ. FITZSIMMONS,g. LANGEN, --. 1992. Protocol for surveying proposed manage- AND R.H.M. ESPIE. 1997. Habitat associations of the ment activities that may impact Northern Spotted Barred Owl in the boreal forest of Saskatchewan, Can- Owls (Revised). U.S. Fish Wildl. Serv., Portland, OR ada. J. RaptorRes. 31:253-259. U.S.A. MEYE•t,J.S., L.L. IRWIN,AND M.S. BOVCE.1998. Influence WASHINGTON STATE FORESTPRACTICES BOARD (WSFPB). of habitat abundanceand fragmentationon Northern 1996. Final environmental impact statement on fbrest Spotted Owls in western Oregon. Wildl. Monogr 139: practicesrule proposalsfor: Northern Spotted Owl, 1-51. Marbled Murrelet, Western Gray Squirrel. Wash. ROHWER, S.A. 1972. A multivariate assessment of inter- Dept. Nat. Resources,Olympia, WA U.S.A. breeding between the meadowlarks, Sturnella.Syst. WRIGHT, A.L. AND G.D. HAYW•V,I). 1998. Barred Owl Zool. 21:313-338. range expansioninto the central Idaho wilderness.J. SHARP,D.U. 1989. Range extensionof the Barred Owl in RaptorRes. 32:77-81. westernWashington and first breeding record on the OlympicPeninsula. J. RaptorRes. 23:179-180. Received28 January 1999; Accepted 1 August 2000