Status of Owls in the Glass Mountain Region, Mono County, California

WESTERNB

Volume 29, Number 1, 1998

W. DAVID SHUFORD, Point Reyes Bird Observatory,4990 ShorelineHighway, StinsonBeach, California 94970 SAM D. FITTON, Bureau of Land Management,20 Hamilton Court, Hollister, California 95023

In east-centralCalifornia, avifaunal surveys have been conductedrecenfiy in the White-Inyo Range (Johnsonand Cicero 1986, 1991) and in the Yosemiteregion and adjacenteast slope of the Sierra Nevada (Gaines 1988). Knowledgeof the distributionand abundance of mostspecies of owls in theseareas appears to be basedon limitedsurveys or compilationsof anecdotalobservations. Shuford and Metropulos(1996) reported on the firstfive yearsof a breeding-bird-atlasproject in the GlassMountain region of Mono County, California. Here we present the resultsof intensive nocturnalowl surveysconducted as part of that ariasproject in 1995 and 1996, supplementedby incidentalobservations of owlsfrom diurnal surveys of all speciesfrom 1991 to 1996. We describethe distribution,elevational breedinglimits, relative abundance,and general habitat requirementsof owlsin the GlassMountain region, compare this knowledge to that of owls in nearbymountain ranges, and discussfactors that may limit owlsin the region.Finally, we provideland managers in the regionwith a foundationof knowledgeof owls, previouslylacking, upon which to buildmore detailed studiesneeded to guideland-use decisions.

STUDY AREA AND METHODS StudyArea The GlassMountain study area is locatedin Mono County,California, on the westernedge of the GreatBasin desert and liesbetween the White-Inyo Rangeto the eastand the Sierra Nevadato the west (Figure1). The study area centerson GlassMountain and its spurridges and stretchesfrom the Mono Cratersand Adobe Hills on the north to the upper OwensGorge on the southand from Highway 395 on the westto the eastslope of the Benton

Western Birds 29:1-20, 1998 1 STATUS OF OWLS IN THE GLASS MOUNTAIN REGION, CALIFORNIA

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Figure1. The GlassMountain atlas grid in relationto nearbymountain ranges in east- central California. Contour interval, I000 ft.

Rangeon the east(Figure 2). Elevationsin the studyarea rangefrom a low of about5800 ft in the upper OwensGorge below the Upper PowerPlant to 11,140 ft on the southpeak of GlassMountain. Much of the regionhas been shapedby volcanicactivity. STATUS OF OWLS IN THE GLASS MOUNTAIN REGION, CALIFORNIA

Figure2. GlassMountain region with 5-km atlas grid. Contour interval, 250 ft.

Majorterrestrial habitats (adapted from USFS 1981) include (1) Sagebrushscrub--a moderately open shrubland usually dominated by BigSagebrush (Artemisia tridentata), but other species, such as Bitterbrush (Purshiatridentata) and rabbitbrush(Chrysothamnus spp.), may be domi- nantsor co-dominants.On alkalinesoils, Greasewood ($ar½obatus vermi- ½ulatus)may dominate, as mayRubber Rabbitbrush (C. nauseosus),which alsocolonizes disturbed areas. Other frequent shrubs include Green Ephedra (Ephedraviridis), Hop-sage (Grayia spinosa), Desert Peach (Prunus ander- sonii), and horsebrush(Tetradymia spp.). (2)Pinyon woodland--an open woodland usually dominated by Singleleaf PinyonPine (Pinus monophylla). In thisregion, junipers (Juniperus spp.) are importantat onlyscattered sites, such as low on the eastslope of the STATUS OF OWLS IN THE GLASS MOUNTAIN REGION, CALIFORNIA

BentonRange. Curl-leaf Mountain-mahogany (Cercocarpus ledifolius) may mix with the pinyons locally, and Big Sagebrushand Bitterbrushare important understowshrubs. (3) Mountain-mahoganywoodland--a moderatelyclosed short woodland dominatedby Curl-leaf Mountain-mahogany;Big Sagebrushand Bitter- brushare importantunderstow shrubs. (4) Jeffrey Pine forest--an open forest dominatedby pure standsof primarilysecond-growth Jeffrey Pine (Pinusjeffreyi) with an open under- stow of Bitterbrushand sagebrush. (5) Mixed coniferforest--an open to moderatelyclosed forest of mixed standsof White Fir (Abies concolor)and Jeffrey Pine or LodgepolePine (Pinuscontorta ssp. murrayana).The understowmay be of smallWhite Firs and scatteredshrubs. Of very localoccurrence on the westside of the studyarea. (6) LodgepolePine forest--an open to moderatelydense forest dominatedby LodgepolePine. Importantunderstow shrubs are Big Sagebrush, Bitterbrush,and, locally,currant (Ribes spp.). (7) Limber Pine forest--an open subalpineforest dominated by Limber Pine(Pinus fiex!lis) found locally on dry steepslopes at highelevations. At the lower extentof its altitudinalrange, Limber Pine mixeswith Lodgepole Pine. The understowmay be open or of scatteredBig Sagebrushbushes. (8) WhitebarkPine forest/woodland--ashort subalpineforest or woodlanddominated by WhitebarkPine (Pinusalbicaulis), found only in patches on the top of GlassMountain. (9) Riparian forest/woodland--adense to moderatelyopen forest or woodlanddominated by deciduoustrees or shrubs,including willows (Salix spp.), Quaking Aspen (Populus tremuloides), Black Cottonwood (P. balsamiferassp. trichocarpa), Wild Rose (Rosa woodsii var. ultramontana), Water Birch(Betula occidentalis),and, locally,Buffalo Berry (Shepherdia a rgen tea). (10) Dry meadow--a meadow that supportsbunch grasses,annual grasses,and someforbs and shrubs;sedges (Carex douglasii)and rushes (•luncusspp.) tolerant of relativelydry conditionsmay mix with the grasses. Saltgrass(Distichlis spicata) dominates on salinealkali fiats. The underlying water tablefluctuates seasonally. (11) Sand fiat--pumice sand flats are coveredsparsely with perennial forbs, such as Pussypaws(Calyptridium umbellatum), Hulsea (Hulsea vestita),evening primrose (Oenothera spp.), Mono Lake Lupine(Lupinus duranii), and Mono Milkvetch(Astragalus monoensis). (12) Wet meadow--a meadow thickly vegetatedwith relativelyshort perennialsedges, rushes, and grasses that occurson levelor gentlysloping areaswith a year-roundsource of water.Small forbs are alsocommon. (13) Perennialgrassland--limited areas dominated by nativegrasses are foundin the sagebrushzone where fire or otherdisturbance has occurred. (14) Alpinefell-field•n the top of GlassMountain dry open pumicesoil supportsscattered patches of variousperennial herbs and grasses. (15) Barren areas--includeareas largely devoid of vegetativecover, such as rock outcrops,rocky cliffs, earthen bluffs, talus slopes, volcanic craters, and some sand or alkali fiats. STATUS OF OWLS IN THE GLASS MOUNTAIN REGION, CALIFORNIA

Important wetlands--open water of lakes, ponds, and streamsand associatedmarshes and wet meadows--are found in Adobe Valley to the north of Glass Mountain and to the west and south in the Owens River/ CrowleyLake drainageof LongValley and the OwensGorge. The studyarea is managedprimarily by the U. S. ForestService/Inyo National Forest, Bureau of Land Management,and Los AngelesDepart- ment of Water and Power. Human habitation is minimal and clustered mostlyin the LongValley region in the southwesternportion of the study area, thoughhuman influence is widespread.Cattle grazing is extensivein meadowsand riparianzones. Heavy logging, particularly of JeffreyPines, coupledwith fire suppressionover the last100 yearshas greatly altered the remainingforests, leaving denserstands of smaller-diametertrees than existedhistorically (T. Higley pers. comm.).

Data Collection Atlas grid. As in manyother California atlas projects, the studyarea was dividedby a gridof 5-km (3.11 rni)squares or blocksbased on the Universal TransverseMercator grid tick marks on 15-minute USGS topographic maps. The studyarea thus comprises63 completeand 11 partialblocks (Figure2). Theseblocks were the basicunits of fieldwork and for mapping the distributionof all speciesof owls. Nocturnal surveys.In 1995 and 1996, 14 observersspent about 190 hoursconducting nocturnal surveys for owls;we accountedfor 74% of this total.Surveys were conductedprimarily by drivingthe extensivenetwork of dirt loggingroads in the studyarea and stoppingat irregularintervals in seeminglysuitable habitat to try to detectowls. Because of steepterrain and a virtuallack of two-wheel-driveroads above 9200 ft, Shufordbackpacked overnighton 7 July 1996 to an unnamedpeak at 9961 ft aboveupper Wilfred Canyon and on 9 July 1996 to the upper elevationallimits of Sentinel Meadow ResearchNatural Area at 10,171 ft. At lower elevations, observersalso occasionallywalked up to 1.5 mi. off roads,particularly on nights of or close to full moons. Also, a few owls were encountered fortuitouslyat night at camp sites.All nocturnalsurveys were conducted from 27 April to 29 July (Figure3). Althoughsome owls were recordedfrom spontaneousvocalizations, ob- serversattempted to elicitresponses from owlsby playingtape-recorded calls or makingvocal imitations of the variousspecies. Because observers were so few, we focusedon spreadingcoverage throughout all atlas blocksand elevationsrather than on standardizedroutes and call points aimed at randomizingobservations and documenting call frequencies over the season. Diurnal coverage.From 1991 to 1996, observersspent 1861 hours conductingmulti-species diurnal surveys for breedingbirds in the studyarea. Althoughnot ideal for detectingnocturnal species, these diurnal surveys providedimportant supplemental data on certainspecies of owls.We were ableto covermost habitats in all blocks,except in riparianor wetlandhabitat in partsof three blocksalong about a 7-mile stretchof privateland on the upper OwensRiver. Methods used were similarto thosefollowed by most breeding-bird-atlasprojects in North America(Laughlin et al. 1982, 1990), as summarizedby Shufordand Metropulos(1996). For eachblock, observ- STATUS OF OWLS IN THE GLASS MOUNTAIN REGION, CALIFORNIA

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Figure3. Numberof hoursspent on nocturnalowl surveysby 1O-day periods from April throughJuly, 1995 and 1996. ers recordedthe most conclusivetype of breedingevidence observed for each speciesencountered. Observers attempted to obtainadequate cover- ageof eachblock by visitingall habitatspresent until knowledge of species- habitatassociations suggested that furtherfield work was unlikelyto add many breedingspecies to a particularblock (see Shuford 1993:46-48) Nevertheless,as in all ariasprojects, no matterhow thorough,we assumed that somebreeding species likely were missedin manyblocks, particularly difficult-to-surveyspecies such as owls.Likewise, because habitat, climate, prey populations,and otherconditions change over time, speciesrecorded in a blockduring the ariasperiod may not necessarilybe foundthere in subsequentyears. Other informationcollected. On eachvisit to a block,whether nocturnal or diurnal,observers recorded (1) the elevationalbreeding limits (to the nearest100 ft) of all speciesencountered, (2) the numberof hoursspent in the field(to the nearest1/4 hr) as a measureof observereffort, (3) a count or estimateof the numberof eachspecies observed or heard,and (4) details of all confirmedbreeding records. Elevations were estimatedin the field from topographicmaps or a calibratedaltimeter. Observers also recorded whetherowls were detected aurally and/or visuallyand, to the bestof their ability,the habitatsfrom whichowls were vocalizing. Incidentalsightings. We alsoaccepted any breedingevidence observed outsideof regulararias surveys that could be accuratelyassigned to a specific block.Such information was obtained by ariasparticipants in the courseof miscellaneoustravels or other field work or by reliableobservers who transmittedtheir observationsto ariasparticipants. Relatiue distribution.In speciesaccounts the relativeextent of each species'breeding distribution within the studyarea is describedby meansof STATUS OF OWLS IN THE GLASS MOUNTAIN REGION, CALIFORNIA a rankingof the numberof blocksin whichthe speciesoccurred: very local -- 1-15 blocks,local -- 15-30 blocks,fairly widespread-- 31-45 blocks, widespread-- 46-60 blocks,and nearlyubiquitous -- 61-74 blocks. Estimatesof owl numbers.The total numbersof each speciesof owl recordedon bothnocturnal and diurnal surveys were converted to estimates of owl territories;these are not estimatesof pairsof owls,as some territorial owlsmay not be paired,or of the total numberof owl territorieswithin the ariasstudy area. To make theseconversions we assumedthat (1) two owls callingat differentpitches and cadencesrepresented mated pairs on a mutualterritory and (2) singleadults, whether recorded by callor by sight, alsorepresented one owl territoryregardless if they were pairedor not. Groupsof fledglings,whether or not accompaniedby adults,also obviously representedmated pairs on territory. Comparative data. To obtain historicalrecords of owls in the Glass Mountainarea and informationon the statusof owlsin nearbymountain rangesin California(White-Inyo Range, Mono and Inyo counties;eastern SierraNevada, Mono and Inyo counties;and SweetwaterMountains, Mono County) (Figure 1), we searchedthe publishedliterature, combed the unpublishedfiles of the editorsfor the middle Pacific coast region of National Audubon SocietyField Notes, correspondedwith localexperts, and obtainedspecimen and egg-setdata from the Los AngelesCounty Museumof NaturalHistory (LACM), Museum of VertebrateZoology (MVZ), San Bernardino County Museum (SBCM), San Diego Natural History Museum(SDNHM), Santa BarbaraMuseum of Natural History (SBMNH), and Western Foundationof VertebrateZoology (WFVZ). Recordsfrom American Birds are citedas AB: page number. Observerscited: A1 DeMartini (ADeM), Anthony Desch (ADes), Sam D. Fitton (SDF), Helen and Paul Green (H & PG), Mike McClaskey(MMcC), DebraLove Shearwater (DLSh), Dave Shuford (DS), and Emilie Strauss (ES).

RESULTS AND DISCUSSION

We recordedseven species of owl in the studyarea and know of the historicaloccurrence of one additionalspecies, the Short-eared.From our detectionrates, the NorthernSaw-whet was the mostabundant, followed by the Great Horned, Long-eared,Flammulated, Western Screech, Northern Pygmy,and Barn. The firstthree were numerousand fairlywidely distrib- uted,whereas the otherswere rare and occurredvery locally.Although we confirmedbreeding of onlythe threemost numerous species, circumstantial evidencesuggests the remainingspecies also breed in the studyarea. A declineof breedingShort-eared Owls throughoutCalifornia (see account) may explain our current inabilityto find this species.Alternatively, the speciesmay breedin the studyarea irregularly,depending on upswingsin cyclesof rodentabundance (Clark 1975, Voous1988), aswe haveobserved elsewherein California.Also, we documenteda range extensionof a subspeciesof the Western Screech-Owl,presumably Otus kennicottii inyoensis(Grinnell and Miller 1944), if thisis adequatelydifferentiated from aikeni (Marshall 1967). STATUS OF OWLS IN THE GLASS MOUNTAIN REGION, CALIFORNIA

SpeciesAccounts Barn Owl (Tyto alba) A verylocal breeder (possibly a transient) recorded in only1 (1.4%)of 74 ariasblocks (Figure4). Our onlyrecord was of a singleindividual heard on a nocturnalsurvey at about6200 ft inthe upper Owens Gorge above the Upper Power Plant on 4 May 1996 (SDF).The habitaton the slopesof the gorgeis dominatedby sagebrushscrub with scatteredpinyon and Jeffrey pines; clumps of willowsand wet sedgemeadow line the riverbelow. Numerous potential nesting cavities are preser•tin the extensiverock cliffs of theOwens Gorge. This location may be at theupper elevational limit of thisspecies' breedingin California.Grinnell and Miller (1994) listedthe upperelevation of known "occurrence"as 5500 ft in the southernSierra. Gaines (1988) considered the species a rare transientup to 6500 ft in the Mono Lake area, but hisApril to Junerecords suggestthe possibilityof occasionalbreeding at thatelevation. The speciesis a "fairly common"nesting bird to thesouth in the Owens Valley (T. and J. Heindelpers. comm.) but isunrecorded in the adjacentWhite-Inyo Range (Johnson and Cicero 1986, T. and J. Heindel pers. comm.). Likewise,we know of no recordsfor the Sweetwater Mountains,though the specieswas seenon 10 September1995 in the Bridgeport Valley(P. J. Metropulospers. comm.) at the baseof that range. FlammulatedOwl (Otus flarnmeolus) A verylocal breeder recorded in 4 (5.4%)of 74 ariasblocks (Figure 4). Represen- tative locations were about 1.5 mi. NE of Indiana Summit Research Natural Area (8300 ft, callingadult, 25 June1995, DS),Sagehen Meadow (8400 ft, callingadult, 25 Juneand 10 July1995; DS, DLSh),Wet Meadow(8800 ft, callingadult, 4 July 96, SDF et al.),about 1 mi. N of SawmillMeadow (8600 ft, agitatedadults, 11 July 1995; ADeM, DLSh),and about 0.5 mi. NW of SawmillMeadow (9200 ft, pair, 10 June 1995, SDF). On nocturnalsurveys, we detectedeight vocalizingbirds (one subsequentlyseen) representing seven Flammulated Owl territories.Of these, five werein mixedgroves of aspensand either Jeffrey or Lodgepolepines; two werein pure standsof JeffreyPine forest.On 13 June 1992, D. and J. Parker(in litt.) found the wingof a FlammulatedOwl at 8000 ft in a mixedwoodland of QuakingAspen, BlackCottonwood, juniper, and JeffreyPine in an unnamedcanyon southeast of O'HarrelCanyon; identification of thewing was confirmed by T. andJ. Heindel(pers. comm.).Grinnell and Miller (1944) reportedspecimens collected on 20 and 22 June 1942 from 9 mi. W of Benton(8300 ft; MVZ 84823, 84824). A. H. Miller'sfield notes(MVZ library) indicate that on these dates he andW. C. Russellwere camped out in an aspengrove off the road to SawmillMeadow on the northeastflank of Glass Mountain.They heard Flammulated Owls calling in Ponderosa[Jeffrey] Pine both on the edgeof the aspengrove and up the drainageabout one-quarter mile. Knowledgeof the species'habitat requirements in Californiais still incomplete, and morework is needed to confirmthe extentof the species'apparent strong association in ourstudy area with aspen-pine groves. Grinnell and Miller (1944) described breeding habitatas openor brokenforests of variousconifers often mixed with CaliforniaBlack Oak (Quercuskelloggii) or Oregon Oak (Q. garryaria).Though recognizingthe vegetativediversity of theFlammulated owrs breedinghabitat, Winter (1974) reported itsclose association in Californiawith yellow pine (P. ponderosa and P. jeffrey/). Black Oak, thoughtto be importantfor nestcavities, is a co-dominantwith Ponderosa Pine in breedinghabitat in northwesternCalifornia (Marcot and H•111980). Quaking Aspen is a keynesting tree in Idaho(Powers et al. 1996) andColorado, where Webb (1982) also founda closeassociation between this owl and the aspen-pine e•otone. Gaines(1988) listedthree May-to-Augustrecords from 6400 to 8200 ft in the easternSierra of MonoCounty; also, a specimenwas obtained 3 May 1983 at 9000 ft at LakeGeorge, Mammoth Lakes (LACM 103003). Similarly,T. andJ. Heindel(in litt.) STATUS OF OWLS IN THE GLASS MOUNTAIN REGION, CALIFORNIA STATUS OF OWLS IN THE GLASS MOUNTAIN REGION, CALIFORNIA knowof onlythree May-to-July records from 8200 to 9700 ft in the easternSierra of Inyo County.The FlammulatedOwl is unrecordedfrom the SweetwaterMountains (Winter 1974, Johnson1975). Kenyon(1947) founda dead FlammulatedOwl in a LodgepolePine forestat 9500 ft on the westslope of the southernSierra, Fresno County.But far and awaythe highest-elevationbreeding record is of a nestwith two youngobserved from 10 Julyto 7 August1990 in a WesternBrisfiecone Pine (Pinus Iongaeva)at 10,500 ft in SchulmanGrove of the WhiteMountains, Inyo County(AB 44:1187, T. andJ. Heindelpers. comm.); the speciespreviously was unrecorded from thesemountains (Winter 1974, Johnsonand Cicero 1986, 1991). It is unclearif sites meeting the FlammulatedOwI's insectivorousniche are localizedat these higher elevationsor if otherfactors explain the species'patchy distribution at theseelevations in the Great Basin.

Western Screech-Owl(Otus kennicottii) A verylocal breeder recorded in 3 (4.0%)of 74 atlasblocks (Figure 4). Ouronly records werefrom 2 mi. NNE of the peakof GraniteMountain (7000 ft, duettingpair, 7 June 1996, DS), north-facingslope of ChidagoCanyon about 1.5 mi. E of AntelopeSpring (6400-6600 ft, twoduetting pairs, 26 Mayand 28 June1996, SDF),and 1 mi.WSW of the peakof CasaDiablo Mountain (6900 ft, callingadult, 5 May 1996, DS).On nocturnal surveys• detectedseven vocalizing birds (one also seen) representing four screech-owl territories.Also, I. Mandelbaum(in litt.)heard a screech-owlin the AdobeHills, about 8- 9 mi. E of MonoLake and 2-3 mi. S of DeepWells, just north of ourstudy area, on 10 April 1996. Theserecords extend the rangeof the WesternScreech-Owl about 40-50 mi. NNW to NW,respectively, of the previously known northern limits of thesubspecies O.k. inyoensisin Californianear Bishop in the OwensValley and the WhiteMountains, Inyo County(Grinnell and Miller 1944, Miller and Miller 1951, Johnsonand Cicero 1986);the subspeciesalso occurs to the northin Nevada(Alcom 1946). All screech-owlswere found in pinyonwoodlands ranging from large, moderately denseto small,very open stands;the owrs densitieswere very low, as appearsto be typicalin thishabitat elsewhere (Marshall 1967, J. Marshallpers. comm.). We didnot detectscreech-owls in grovesof Black Cottonwood,Quaking Aspen, or willows, thoughthe owl is foundin deciduoustrees at lowerelevations in the OwensValley (T. and J. Heindel pers. comm.). Millerand Miller(1951) andJohnson and Cicero(1986) recordedthe speciesup to 8250 ft in the White Mountains,where the latter authors consideredthe species "uncommon."Thus, the low densitieswe detectedpresumably reflect the statusnear the upperelevational limit of thissubspecies. The few recordsof screech-owlson the eastslope of the centralSierra Nevada, Mono County,appear to representtransient individuals(Gaines 1988), andthe speciesis unrecorded in the SweetwaterMountains (N. K. Johnsonin litt.). Efforts should be made to find screech-owlselsewhere in California east of the Sierra Nevada,as we knowof observationsof thisspecies on the eastslope of the Sierra,Inyo County(T. and J. Heindelin litt.), in Siena Valley,Plumas County (L. Jensenpers. comm., Shufordpers. obs.),and in the Susanville-Janesvillearea, LassenCounty (B. Stovallin litt.),outside the species'range as mapped by Grinnelland Miller (1944). Great Horned Owl (Bubovirginianus) A fairlywidespread breeder recorded in 41 (55.4%)of 74 atlasblocks (Figure 5). Locationsranged in elevationfrom 5800 ft (canyonin BentonRange above Benton Hot Springs,fledglings, 2 June1992, DS) to 9200 ft (SawmfilMeadow, calling adult, 29 June 1996; SDF,ADes). We encounteredabout 61 adult-sizedbirds and 14 fledglings representingabout 56 territories.Of these,20 adult-sizedbirds and 9 fledglingswere from daytimeobservations (13, 9) or frommiscellaneous dusk or nocturnalsightings (7, 0), and41 adult-sizedbirds and 4 fledglingswere from nocturnal surveys.

10 STATUSOF OWLSIN THE GLASSMOUNTAIN REGION, CALIFORNIA

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11 STATUS OF OWLS IN THE GLASS MOUNTAIN REGION, CALIFORNIA

Of four nestsfound, one wasin an old raptornest in a largeJeffrey Pine and three were in cavitiesin rockycliffs surrounded in two casesby sagebrushscrub and in the otherby sagebrushand Jeffrey Pine forest. Of fiveadditional fledged broods, one was seen in an aspen grove, two were seen in rocky canyonssurrounded by either sagebrushscrub or pinyon woodland,and singlejuveniles were heard in pinyon woodlandand JeffreyPine forest,in both caseswith rockycliffs in the vicinity. Adult Great Horned Owls were foundin almostall terrestrialhabitats up into the lodgepolezone. Of 45 recordswith adequatehabitat data, 14 were in pinyon woodland,14 were in JeffreyPine forest,8 were in sagebrushscrub or sandflats, 5 werein forestsof JeffreyPine mixed with SingleleafPinyon Pine, Lodgepole Pine, or White Fir, 2 were in LodgepolePine forest,and 2 were in standsof variouspines mixedwith aspens. Johnsonand Cicero(1986) consideredthe Great Horned Owl a "fairlycommon" breederup to 9500 ft in the White-InyoRange, and Gaines (1988) termedthe species a "fairly commonresident below 7000 ft and uncommonresident or visitorto treeline"in the easternSierra Nevada. Gaines had recordsof callingbirds at 10,000 ft in February,when birdsshould be pairing,but knewof no confirmedevidence of breedingabove 7400 ft; subsequenfiy,a successful nest was observed in spring1990 at 8400 ft in the town of Bodie (P. Nicholsonfide ES). Great Horned Owls alsooccur in the SweetwaterMountains (e.g., 2 calling,9400 ft, 3 mi. S of LobdellLake, 4 June 1996; ES, MMcC).

Northern Pygmy-Owl(Glauciclium gnoma) A very local breederrecorded in 2 (2.7%) of 74 ariasblocks (Figure 5). The two recordsare from TaylorCanyon (7300 ft, callingadult, 23-24 June 1994, DS) and WildroseCanyon (7700 ft, callingadult, 12 June 1995; DLSh, ADeM). These individuals,both encountered during the day, were in aspengroves bordered either by pinyonwoodland (heard only) or a mixedwoodland of Jeffreyand pinyonpine (seen and heard).N. K. Johnson(in litt.) alsocollected a Northern Pygmy-Owlon 6 June 1970 at 8600 ft at Wet Meadow (MVZ 162393). Gaines(1988) consideredthis speciesa "rare resident"on the east slopeof the SierraNevada to 8000 ft and citeda suspectednesting location, in our studyarea, at 7800 ft at O'Harrel Canyon.Similarly, T. and J. Heindel(pers. comm.) know of only four recordsfor the easternSierra of Inyo County,including a copulatingpair on 8 April 1995 (E. A. Cardiff)and a familygroup on 12-13 July 1997 (S. Blanchard), bothat 7800 ft at GlacierLodge 8.5 mi. WSW of Big Pine. The speciesalso seems relativelyrare in the White-InyoRange. Records for the Inyosinclude an individual seenat 7100 ft at Upper AddleSprings on 5 August1975 (D. Julianifide T. and J. Heindelpers. comm.), a specimenfrom a pinyon-juniperwoodland at 7700 ft near WaucobaMountain on 27 June 1977 (Johnsonand Cicero 1986), andone in pinyon woodlandat 8500 ft eastof Lone Pine on 16 June 1978 (AB 32:1209). We know of onlyone validrecord from the White Mountains,Inyo County:a birdcalling at 8400 ft at GrandviewCampground on 23 May 1987 (AB 41:1488). Hall et al. (1991) listed severalreports for the White Mountains,but theseneed furtherconfirmation given that theseauthors listed a numberof questionablerecords for other speciesøThe NorthernPygmy-Owl also occurs in the SweetwaterMountains (Johnson 1975). We suspectthe species'rarity in the GlassMountain region and othernearby mountain rangesmay reflect, in part,declining abundance with elevation,as it isnumerous only to about6000 ft nearbyon the westslope of the Sierra Nevada(Gaines 1988).

Long-earedOwl (A$io otus) A fairlywidespread breeder recorded in 33 (44.6%)of 74 ariasblocks (Figure 6). Notablerecords were from Antelope Spring (6500 ft, fledglings,12 June1994, H & PG), SawmillMeadow (9100 ft, family group, 30 July 1992, J. Blanchardfide

12 STATUS OF OWLS IN THE GLASS MOUNTAIN REGION, CALIFORNIA

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13 STATUS OF OWLS IN THE GLASS MOUNTAIN REGION, CALIFORNIA

D. Parker),and unnamedpeak aboveupper WilfredCanyon (9900 ft, pair, 7 July 1996, DS).We encounteredabout 45 adult-sizedbirds and 21 fledglingsrepresenting about 42 territories.Of these, 28 adult-sizedbirds and 14 fledglingswere from daytimeobservations (25, 14) or from miscellaneousdusk or nocturnalsightings (3, 0), and 17 adult-sizedbirds and 7 fledglingswere from nocturnalsurveys. Of five nestsdetected, two were in old Black-billedMagpie (Pica pica) nestsin willow-wildroseor Water Birch riparian borderedby wet meadowand sagebrush scrub,one was on a platformresembling an old squirrelnest in a LodgepolePine forestadjacent to a wet meadow,one wasin an old corvidnest in one of a few dense pinyonson the edgeof an openJeffrey Pine forest bordered by Bitterbrush-sagebrush scrub,and one wasin a cavityat the top of a JeffreyPine snag in a mixedstand of JeffreyPines and White Firs.Another probable nest site also was in a cavityatop a JeffreyPine snag in an openJeffrey Pine forest near sagebrush scrub. Of sixbroods foundout of nests,four were in willow-wildroseor BuffaloBerry riparian, one wasin mountain-mahoganyin a JeffreyPine-sagebrush matrix, and for one we lackspecific habitatdata. Although 50% of nestsand broodswith adequatehabitat data were in lowlandriparian groves, which provide the owlsmany nest platforms from old magpie nestsand presumablya good prey base in adjacentmeadows and sagebrush,we suspectthese data overemphasizethe importanceof riparianhabitats to theseowls. First,riparian habitats, including aspen groves, account for lessthan 1% of the extent of potentialLong-eared Owl habitatin the studyarea, and, second,owl nestsand broodsare much easierto find in the thin stringersof short riparian habitat that predominatein thisregion than in extensivestands of other forestsand woodlands. When the owlsdid not nestin relativelyopen forests,the densestands of treeswhere theynested were usually adjacent to or closeto wet or drymeadows, sand fiats, open sagebrushscrub, or otheropen foraging areas. Of 29 other recordsof these owls with adequatehabitat data, 7 were from LodgepolePine forest,6 from JeffreyPine forest,5 from sagebrushscrub, 4 from riparianthickets, 2 from pinyonwoodland, 2 from mountain-mahoganywoodland/ sagebrushscrub edge, 1 frommixed Lodgepole-Jeffrey Pine forest, 1 frommountain- mahoganywoodland, and 1 froma mixedaspen/lodgepole forest on a meadowedge. Gaines (1988) consideredthe Long-earedOwl "a locallyuncommon summer resident"to 8000 ft in the easternSierra Nevada, and Johnsonand Cicero (1986) termedthe species"an uncommonresident" to 9500 ft in the White-InyoRange. Recordsfrom the White Mountainsof singleindividuals on 26 May 1919 at an unspecifiedlocation at 10,500 ft, Mono County(Dawson 1923, Grinnelland Miller 1944), and on 18 July 1997 at 10,400 ft at SilverCanyon, Inyo County(T. and J. Heindelpers. comm.), suggest possible nesting at theseelevations. The statusof this speciesin the SweetwaterMountains is uncertain,though habitat conditions suggest it is justas numerousthere as it is near GlassMountain. Large declines in breeding populationsof the Long-earedOwl have led to the species'designation as a Bird Speciesof SpecialConcern in California(Remsen 1978, S. Laymonpers. comm.). Gaines(1988) documentedhistorical declines near Mono Lake causedby habitat destruction,but thisis likelya localeffect given our recentobservations nearby in the GlassMountain area. Grinnelland Miller(1944) considered"the northernGreat Basin territory"to be among the species'"centers of abundance"in the state. Our observations,showing the GlassMountain region currenfiy to be a centerof abun- dancein the state,and those of othersto the northand south (Remsen 1978, Johnson and Cicero 1986, T. and J. Heindel in litt.) indicatethe speciesprobably is still numerousin the GreatBasin portions of Californiaall alongthe Cascade-Sierraaxis. Bloom(1994) consideredhabitat loss from urbandevelopment and agricultureto be the main causeof populationdeclines of breedingLong-eared Owls in coastal southernCalifornia. Besides residing in areasfar fromurban centers and large-scale agriculture,Long-eared Owls in the Great Basinof Californiamay benefitfrom a diverseand abundantprey base.Species richness of mammals,the owl's principal

14 STATUS OF OWLS IN THE GLASS MOUNTAIN REGION, CALIFORNIA prey (Voous 1988), at the Great Basin-Sierraecotone is among the highestin California(Howell 1924, Smith 1979) and in North America (Simpson1964). Althoughthe diet of Long-earedOwls near GlassMountain is unknown,the area's smallmammal faur•a is not only rich but includesseveral heteromyid rodents, long- lived specieswith life historiesthat tend to dampen their populationfluctuations (Brown and Harney 1993). In the desertsof Idaho, where Long-earedOwls are numerousand breedregularly (Marks 1986), the speciespreys on a wide varietyof smallmammals, but primarilyon aboutequal proportions of deer mice(Peromyscus), pocketmice (Perognathus),and kangaroorats (Dipodomys)(Marks 1984). These rodentsare numerousin the Mono Lake-GlassMountain area (Howell 1924, Harris 1982), and the diet of winteringLong-eared Owls in the southernCalifornia deserts is totally dominatedby the two heteromyidgenera Perognathus and Dipodomys (Barrows1989). By contrast,in muchof their range,where they dependon highly fluctuatingpopulations of voles(•licrotus), Long-earedOwl populationsfluctuate correspondingly(Voous 1988).

Short-earedOwl (Asio flammeus) We did not record this specieson our surveysof potentialbreeding habitat of marshesin Long and Adobe valleys.Dixon (1934) reportedvarious records from "withina twenty-mileradius of June Lake," includinga nest of a Short-earedOwl foundon 15 June 1933. Althoughthe exactlocation of this sightingis uncertainit may havebeen within the westernboundary of our studyarea. Also, Rowley(1939) reporteda Short-earedOwl nestfound on 19 May 1926 in a meadownear McGee Creek, Long Valley(WFVZ 26579), which apparentlywas within or just outsidethe westernboundary of our studyarea. The only recentevidence of breedingof this specieseast of the centralSierra Nevada is the observationof two birdscourting at 6500 ft in BridgeportValley in 1984, thoughthere are alsoa few breeding-season observationsfor 6400 to 6500 ft at Mono Lake (Gaines1988; AB 45:493, 1158). A breeding-seasonrecord for the OwensValley is of an individualseen 3 mi. NE of Big Pineon 20 June1978 (T. andJ. Heindelpers. comm.). We knowof no recordsof this speciesfrom the SweetwaterMountains, and its statusin the White Mountainsis uncertain(Johnson and Cicero 1986). Becauseof statewidedeclines of breeding Short-earedOwls, the speciesis listed as a Bird Species of Special Concern in California(Remsen 1978, S. Laymonpers. comm.).

Northern Saw-whetOwl (Aegoliusacadicus) A fairlywidespread breeder recorded in 38 (51.4%) of 74 ariasblocks (Figure 6). Notablerecords were from the upper Owens Gorge abovethe Upper Power Plant (6400 ft, callingadult, 4 May 1996, SDF),McGee Canyon (7800 ft, nestwith young, 8-12 June1995; DLSh, ADeM), andabove Wilfred Canyon and E of GlassMountain Ridge(9800 ft, callingadult, 7 July 1996, DS). We encounteredabout 84 individuals representingabout 72 territories.All were on nocturnalsurveys except for a pair at a nesthole 15 ft up in a JeffreyPine and an adultroosting in an aspengrove in the daytime.Gaines (1988) reported a record of a family group at 9500 ft on Glass Mountain,but that elevationis in error and probablywas about9000 ft (R. Stallcup pers. comm.). Saw-whetOwls breedin a wide rangeof forestsand woodlandsof varyingage, stature,and openness.Of 70 recordswith adequatehabitat data, 27 were from JeffreyPine forest,15 from pinyonwoodland, 11 from LodgepolePine forest,10 from mixedstands of JeffreyPine, LodgepolePine, or White Fir, and 7 from stands of QuakingAspen or aspenmixed with Lodgepoleor Jeffreypine. Gaines(1988) deemedthe statuseast of the Sierrauncertain, but felt the species was "probablya rare summerresident" up to about8500 ft. He listeda few nesting recordsfor the eastslope of the SierraNevada to whichwe canadd two more:an adult

15 STATUS OF OWLS IN THE GLASS MOUNTAIN REGION, CALIFORNIA at a nesthole 8.2 ft up in an aspentree near the Log Cabin Mine Road in lowerLee ViningCanyon (7800 ft, 6-10 June1996, K. Farwell)and a nestwith eggsand young about 40 ft up in a JeffreyPine snag cut down by a woodcutterat GlassCreek Campground(7500 ft, 15 May 1995, L. Trefry).In theeastern Sierra of lnyoCounty, twojuveniles were found at 10,100 ft in LodgepolePine forest at GoldenTrout Camp SW of LonePine 13-14 August1984 (AB39:98, T. andJ. Heindelin litt.).Johnson and Cicero (1986, 1991) consideredthe speciesan "uncommonresident" to about 9000 ft in the White Mountains. Saw-whets also occur in the Sweetwater Mountains (Johnson1975), wherea specimenwas taken on 3 July1946 fromWhitebark Pines at 10,000 ft in SweetwaterCanyon, Mono County(MVZ 98334).

SpeciesLimits We suspectthat the rarity of the Barn Owl, FlammulatedOwl, Western Screech-Owl,and Northern Pygmy-Owl in the Glass Mountain region reflectsa funnelingof thesespecies into fewer and fewer sites that meet their nicherequirements as they reachor approachtheir elevationalor ecological limitsof breeding,perhaps as dictated by preyavailability or climate.Of the four,the three speciesof smallowls depend to varyingdegrees on insect prey (Voous1988), the abundanceof which may be reducedby colder temperaturesat higher elevations.The FlammulatedOwl seemsfurther restrictedprimarily to aspenor aspen-pinegroves, where insect •abundance may be greaterthan in pure pine forests(Webb 1982). in Oregon, FlammulatedOwls prefer warm east, south, or higher slopes,perhaps becauseprey are moreabundant or activethere (Bull et al. 1990). McCallum (1994) felt this owl'supper elevational limits might be set by low nocturnal temperatures(and/or high humidity)as well as food availability.In some areas,competition for nest sit•s with other species of smallowls may restrict FlammulatedOwls to aspengroves where nest cavitiesgenerally are more numerousthan in conifers(Webb 1982). The Northern Pygmy-Owloccurs in the studyarea very locally at riparianor meadowedges, where small birds, and presumablyother prey, are more numerousthan in mostother habitats. Althoughriparian edges may be appealingforaging areas for Pygmy-Owls, they themselvesmay be subjectto predationby Cooper'sHawks, which in the Glass Mountain area breed in most major riparian groves at the elevationswhere the owlswere recorded(Shuford pers. obs.). Barn Owlsmay simplybe limitedby temperatures,which in the ariasarea candrop belowfreezing in any monthof the year,as the speciesis primarily a low-elevationand low-latitudebreeder known to be affectedby cold(Voous 1988). The Great Horned Owl appearsto reacha slightlylower elevational breedinglimit than the Long-earedand Northern Saw-whetowls, perhaps becausethe largermammals that usuallymake up the bulkof the species' diet by mass (Jaksi• and Marti 1984) occur in small numbersat higher elevations.High on GlassMountain we saw few lagomorphsor ground squirrels,species important in the diet of Great Horned Owls in the Lahontan Valley, Nevada (Alcorn 1942). Over broad areas, nest sites appearedto be limitingto all owls, as few were recorded,despite good coverage,in Adobe and Long valleys,where there are few treesand only localized cliffs.

16 STATUSOF OWLS IN THE GLASS MOUNTAIN REGION, CALIFORNIA

Further Work Much more work couldbe doneto refineour knowledgeof thesedifficult- to-studyspecies. Because owls vary their vocalactivity seasonally, tending to call mostfrequenfiy in late winteror earlyspring (e.g., Great Horned Owl, Morrell et al. 1991), our concentrationof fieldwork in June and July may have somewhatskewed our understandingof the relativeabundance of the variousspecies. Surveying owls in the GlassMountain region early in the season,though, will in most yearsbe hamperedby roadsclosed by snow. Also, becauseof the difficultyof conductingnocturnal surveys away from roadsand on the steepslopes of GlassMountain above 10,000 ft, we may have underestimatedthe upper elevationallimits of breeding of some speciesof owlsand missedcovering some habitats at nightthat we surveyed in the day. Constraintsof coveringall atlasblocks with a few field workers likewiselimited our abilityto samplehabitats relative to theiravailability, thus biasingour appreciationof the relativeimportance of varioushabitats to each owl species. More studiesare neededto elucidatethe key habitatrequirements of the variousspecies so that land-managementdecisions can be made without threateningthe viabilityof owl populations.Study of the effectsof grazing and timber harvestingon owlswould be especiallyvaluable, as we know of no publishedstudies on bird responsesto thesepractices in this region.As mostof the extensiveJeffrey Pine forest in the areahas been logged, priority shouldbe givento assessingthe importanceto owlsof old-growthstands versusother seral stagesand to the featuresof snagsused for nesting.In Oregon, Flammulated Owls prefer to nest in mature forests in large- diametersnags (Bull et al. 1990). An importantfeature of FlammulatedOwl territoriesin northwesternCalifornia is a locallydense clump of tall, mature trees locatednear a break in canopyclosure and vegetationtype; brush cover may provideinsect prey and cover when the birdsforage near the ground (Marcot and Hill 1980). Finally, more diet studiesshould be undertaken. Little work has been conductedon owl dietsin the Great Basinof California(e.g., Aigner et al. 1994), and almostnothing is knownhere aboutthe trophicstructure of the owl communityrelative to itsprey base compared with suchknowledge from similarhabitats in Idaho (Marti et al. 1993).

SUMMARY

As part of a breeding-birdatlas, we documented the distribution, elevationalbreeding limits, relative abundance, and generalhabitat requirementsof owlsin the GlassMountain region of Mono County,California, on the westernedge of the Great Basindesert. We recordedseven species of owls;one other species,the Short-earedOwl, occurredhistorically. Three species(the Great Horned, Northern Saw-whet, and Long-eared)were relativelynumerous and widespreadbreeders; the abundanceof the latter two speciesin this region was not previouslyknown. Four species(the Flammulated,Western Screech,Northern Pygmy, and Barn) that were relativelyrare and localbreeders appear to reachtheir elevationallimits for

17 STATUS OF OWLS IN THE GLASS MOUNTAIN REGION, CALIFORNIA breeding,perhaps as restrictedby prey availabilityor cold temperatures. Also, we documenteda 40- to 50-mile range extensionof the Western Screech-Owl,presumably of the subspeciesO.k. inyoensis.The statusof owls in the GlassMountain region is fairly similarto that in other nearby mountain ranges, but more surveys are needed, particularly in the SweetwaterMountains. Habitat data suggestedthat riparianthickets, aspen groves,and meadowsmay be of particularimportance to breedingowls by providingnest sites and abundantprey. More work is neededto determine the relativeimportance to owlsof variousseral stages of forests,particularly old growth,and to elucidatefeatures of snagsused for nesting.

ACKNOWLEDGMENTS

The followingindividuals helped conductnocturnal owl surveys:AI DeMartini, Anthony Desch, Joel Ellis,Terri Fitton, Hope Fitton, Joan Humphrey, Dan Keller, Don Keller, Mike McClaskey,Peter J. Metropulos,Debra Shearwater,and Emilie Strauss.These individualstook responsibilityfor conductingfield surveysof arias blocks,helped with fieldwork, or providedindividual observations of breedingbirds: Bob Baez, John Blanchard,Carolyn Callahan,Julie Clothier,A1 DeMartini, Sam Fitton, Brian Flaig, Sage Gaines, Helen and Paul Green, Steve Holland, Joan Humphrey,Dan Keller,Don Keller,Roland Knapp, Tony Leukering, Mike McClaskey, MichaelJ. Mammoser,Peter J. Metropulos,Debby and Jim Parker,Lina Prairie, Michael Prather,Bob Richmond,Rusty Scalf, Debra Shearwater,Dave Shuford, Glenn Sibbald,Courmey Smith, Evan Smith, EmilieStrauss, Rob Urry, Brian Voll, Dave Winkler,and Neil Whitehouse.Karen Cebra, Carla Cicero, KristaFahy, Kimball Garrett, Ned Johnson,Bob McKernan,Sam Sumida,and PhilipUnitt provideddata on specimensat their respectiveinstitutions. Ned Johnsonalso facilitated access to field noteson ffie at the Museumof VertebrateZoology, Berkeley. Additional owl recordsfor Mono Countywere providedby Helen Greenfrom a copyof the filesof the editorsfor the middlePacific coast region of National Audubon SocietyField Notes archivedby GoldenGate AudubonSociety and by EmilieStrauss from her personalfiles. Tom and Jo Heindelkindly provided unpublished data on owlsin Inyo County.Rusty Scalf worked tirelessly on developinga GIS databasefor the Glass Mountainatlas project and the mapspresented in thispaper. Forest Service biologists Ginelle O'Connor, Debby Parker, RichardPerioff, and, particularly,Gary Milano providedinformation and were supportiveof our research.Terry Hicks reviewed our descriptionsof vegetationtypes in the studyarea, and John Harrisdirected us to key referenceson mammals.Tom and Jo Heindel, Ned Johnson,Emilie Strauss, Philip Unitt, and Jon Winter providedconstructive comments on earlier drafts of the manuscript.We appreciatethe variousland managers of the ForestService, Bureau of LandManagement, and Los Angeles Department of Waterand Power and selected privateland owners who allowedaccess to landswithout which our studieswould not havebeen possible. We alsoare gratefulto our manyfriends in the easternSierra for theircompanionship and moral support. Field work in 1995 and 1996 wassupported by ChallengeCost-share Agreements between the lnyo NationalForest and Point ReyesBird Observatory(PRBO). This is Contribution725 of PRBO.

UTERATURE CITED

Aigner,P. A., Morrison,M. L., Hall, L. S., and Block,W. M. 1994. Great Horned Owl food habitsat Mono Lake, California.Southwestern Nat. 39:286-288. Alcorn, J. R. 1942. Notes on the food of the Horned Owl near Fallon, Nevada. Condor 44:285-286. 18 STATUS OF OWLS IN THE GLASS MOUNTAIN REGION, CALIFORNIA

Alcorn, J. R. 1946. The birdsof LahontanValley, Nevada. Condor 48:129-138. Barrows,C. W. 1989. Dietsof five speciesof desertowls. W. Birds20:I-I0. Bloom,P. H. 1994. The biologyand current status of the Long-earedOwl in coastal southern California. Bull. S. Calif. Acad. Sci. 93:I-I2. Brown, J. H., and Harney, B. A. I993. Populationand communityecology of heteromyidrodents in temperatehabitats, in Biologyof the Heteromyidae(H. H. Genowaysand J. H. Brown, eds.), pp. 618-65I. Spec. Publ. I0, Am. Soc. Mammalogists. Bull, E. L., Wright,A. L., and Henjum, M. G. I990. Nestinghabitat of Flammulated Owls in Oregon.J. Raptor Res. 24:52-55. Clark,R. J. 1975. A fieldstudy of the Short-earedOwl, Asio flammeus (Pontoppidan), in North America.Wildlife Monogr. 47. Dawson,W. L. I923. The Birdsof California.South Moulton, San Diego. Dixon, J. B. 1934. Recordsof the nestingof certainbirds in easternCalifornia. Condor 36:35-36. Gaines, D. I988. Birdsof Yosemiteand the East Slope, 2nd ed. (revisedI992). ArtemisiaPress, Lee Vining, CA. Grinnell,J., and Miller,A. H. I944. The distributionof the birdsof California.Pac. Coast Avifauna 27. Hall, L. S., Morrison, M. L., and Keane, J. J. I991. The distributionof birdsin the White and Inyo mountainsof California:An update,in Naturalhistory of eastern Californiaand high-altituderesearch (C. A. Hall, Jr., V. Doyle-Jones,and B. Widawski, eds.), pp. 203-245. Univ. Calif. White Mtn. ResearchStation Symposium,vol. 3. Harris,J. H. 1982. Mammalsof the Mono Lake-TiogaPass Region. David Gaines/ KutsaviBooks, Lee Vining, CA. Howell, A. B. 1924. The mammalsof Mammoth,Mono County,California. J. Mammalogy5:25-36. JaksiC F. M., and Marti, C. D. I984. Comparativefood habitsof Bubo owls in Mediterranean-typeecosystems. Condor 86:288-296. Johnson,N. K. I975. Controlsof numberof birdspecies on montaneislands in the Great Basin. Evolution 29:545-567. Johnson,N. K., and Cicero,C. 1986. Richnessand distributionof montaneavifaunas in the White-Inyoregion, California, in Naturalhistory of the White-InyoRange, easternCalifornia and western Nevada, and high altitude physiology (C. A. Hall, Jr. and D. J. Young,eds.), pp. I37-I59. Univ. Calif. White Mtn. Research StationSymposium, August 23-25, I985, Bishop,CA, vol. 1. Johnson,N. K., and Cicero, C. I99I. Breedingbirds, in Natural History of the White-Inyo Range,Eastern California (C. A. Hall, Jr., ed.), pp. 361-436. Calif. Nat. Hist. Guides55. Univ. of Calif. Press,Berkeley. Kenyon, K. W. 1947. Causeof death of a FlammulatedOwl. Condor 49:88. Laughlin,S. B., Carroll, J. R., and Sutcliffe,S. M. I990. Standardizedbreeding criteriacodes: Recommendations for NorthAmerican breeding bird arias projects, in Handbookfor ariasingAmerican breeding birds (C. R. Smith,ed.), pp. 2. I- 2.3. Vt. Inst. Nat. Sci., Woodstock,VT. Laughlin,S. B., Kibbe,D. P., andEagles, P. F. J. 1982. Ariasingthe distributionof the breedingbirds of North America.Am. Birds36:6-19. McCallum,D. A. I994. FlammulatedOwl (Otusflammeolus), in The Birdsof North America(A. Poole and F. Gill, eds.),No. 93. Acad. Nat. Sci., Philadelphia. 19 STATUS OF OWLS IN THE GLASS MOUNTAIN REGION, CALIFORNIA

Marcot,B. G., and Hill, R. 1980. FlammulatedOwls in northwesternCalifornia. W. Birds 11:141-149. Marks,J. S. 1984. Feedingecology of breedingLong-eared Owls in southwestern Idaho. Can. J. Zool. 62:1528-1533. Marks,J. S. 1986. Nest-sitecharacteristics and reproductivesuccess of Long-eared Owls in southwestern Idaho. Wilson Bull. 98:547-560. Marshall,J. T., Jr. 1967. Parallelvariation in North and Middle American screech owls.W. Found.Vert. Zool. Monogr.1:1-72. Marti, C. D., Steenhof,K., Kochert, M. N., and Marks, J. S. 1993. Community trophicstructure: The rolesof diet, body size, and activitytime in vertebrate predators.Oikos 67:6-18. Miller,A. H., andMiller, L. 1951. Geographicvariation of the ScreechOwls of the deserts of western North America. Condor 53:161-177. Morrell,T. E., Yahner,R. H., and Harkness,W. L. 1991. Factorsaffecting detection of Great Horned Owls by usingbroadcast vocalizations. Wildlife Soc. Bull. 19:481-488. Powers,L. R., Dale, A., Gaede,P. A., Rodes,C., Nelson,L., Dean, J. J., and May, J. D. 1996. Nestingand food habits of theFlammulated Owl (Otus fiammeolus), in southcentralIdaho. J. RaptorRes. 30:15-20. Remsen,J. V., Jr. 1978. Birdspecies of specialconcern in California:An annotated list of decliningor vulnerablebird species.Nongame Wildlife Invest., Wildlife Mgmt. BranchAdmin. Rep. 78-1, Calif. Dept. FishGame, Sacramento. Rowley,J. S. 1939. Breedingbirds of MonoCounty, California. Condor 41:247-254. Shuford,W. D. 1993. The MarinCounty Breeding Bird Arias: A Distributionaland NaturalHistory of CoastalCalifornia Birds. Calif. Avifauna Ser. 1. BushtitBooks, Bolinas, CA. Shuford,W. D., andMetropulos, P. J. 1996. The GlassMountain Breeding Bird Atlas: Preliminaryresults, 1991 to 1995. Report to the lnyo NationalForest. Point ReyesBird Observatory,4990 ShorelineHighway, Stinson Beach, CA 94970. Simpson,G. G. 1964. Speciesdensity of North Americanrecent mammals. Syst. Zool. 13:57-73. Smith, A. T. 1979. High localspecies richness of mammalsat Bodie, California. Southwestern Nat. 24:553-555. U.S. Forest Service. 1981. Vegetationresource inventory. Unpubl. report, Inyo NationalForest, 873 N. Main St., Bishop,CA 93514. Voous,K. H. 1988.Owls of the Northern Hemisphere. M.I.T. Press, •ambridge, MA. Webb, B. 1982. Distributionand nestingrequirements of montaneforest owls in Colorado.Part III: FlammulatedOwl (Otusfiammeolus). Colo. FieldOrnithol. J. 16:76-81. Winter, J. 1974. The distributionof the FlammulatedOwl in California.W. Birds 5:25-44.

Accepted3 August 1997