The Condor 91:355-361 0 The CooperOrnithological Society 1989

DISTRIBUTION AND HABITAT USE OF MEXICAN SPOTTED OWLS IN ’

JOSEPH L. GANEY AND RUSSELL P. BALDA Department of BiologicalSciences, Northern Arizona University,FlagstaE AZ 86011

Abstract. Distribution and habitat use of Mexican Spotted Owls (Strix occidentalislu- cida) in Arizona were studied from 1984-1988. Owls were widely but patchily distributed throughout the state except for the arid southwesternportion. Distribution of the owl cor- respondedwith distribution of forested mountains and canyonlandswithin the state. Owls occurredeither in rocky canyons or in any of several forest types, and were most common where unloggedclosed canopy (> 80%) forestsoccurred in steepcanyons. Several forest types provided thesehabitat characteristicsin southernArizona, and owls occurredin all of them. Only unloggedmixed-conifer forest provided these characteristicsin northern Arizona, and most owls (67%) were found in this forest type in northern Arizona. Many owls in northern Arizona (54%) were located in areaswhere timber harvest was either occurringnow or was planned in the next 5 years.Owls could not be located at 27% of the historic sitesresurveyed, indicating that population levels may have declined in Arizona.

Key words: Mexican SpottedOwl; Strix occidentalis lucida; Arizona; distribution;habitat use;population trends.

INTRODUCTION STUDY AREA The Spotted Owl (Strix occidentalis) has been We searchedfor Spotted Owls throughout Ari- the focus of considerable controversy in the Pa- zona. Elevation ranges from 365 to 3,660 m in cific Northwest in recent years. Spotted Owls are Arizona, and climate ranges from tropical-sub- most common in old-growth and mature conif- tropical to arctic-boreal. Vegetation types range erous forestsin this region (Gould 1977, Marcot from Chihuahuan and Sonoran desert scrub at and Gardetto 1980, Forsman et al. 1984), and the lower elevations to alpine tundra on the high- owl populations appear to be declining through- est peaks (Brown 1982). The complex topogra- out the region as timber harvest reduces the phy resultsin a diversemosaic of vegetationtypes. amount of old-growth forest (Gould 1977, Fors- Based on differencesin forest types, the study man et al. 1984). area was divided into two geographic regions, Despite this situation, little attention has fo- northern and southernArizona. The dividing line cused on the Mexican subspeciesof the Spotted ran along the base of the Mogollon Rim, a prom- Owl (S. o. lucida), which inhabits rocky canyon- inent east-west scarp in central Arizona (Fig. 1). lands and coniferous forestsin the southwestern Northern Arizona is dominated by high plateaus United Statesand Mexico (Kertell 1977, Wagner dotted with isolated volcanic mountains and dis- et al. 1982, Webb 1983, Johnson and Johnson sectedby deep canyons. Much of this region is 1985, Ganey 1988, Skaggs 1988). No detailed dominated by extensive forestsof ponderosapine studies have been conducted on this owl, and (Pinusponderosa), often containing an under- little is known of its distribution or ecology. We storyof Gambel oak (Quercusgambelit]. At higher studied distribution and habitat use of Mexican elevations, or in cold air drainages, mixed-co- Spotted Owls in Arizona from 1984-1988. This nifer forestscontaining Douglas fir (Pseudotsugu paper reports on patterns of distribution and menziesii)and white fir (Abiesconcolor) often habitat use, population trends, and ownership dominate. Subalpine spruce-fir forests occur at and management prospectsof areas occupied by still higher elevations, while areasjust below the Spotted Owls. ponderosa pine belt are dominated by pinyon- juniper woodlands (Brown 1982). I Received 16 September 1988. Final acceptance6 Southern Arizona is characterized by isolated February 1989. mountain ranges separated by intervening allu-

13551 356 JOSEPHL. GANEY AND RUSSELL P. BALDA

I trast, extensive areas of old-growth coniferous . : .a. forestshave been harvested in northern Arizona. . . Most recent logging has been done using tractor- yarding systems,and thus has been restricted to Northern Arizona areaswith lessthan 40% slope. As a result, most

” . remaining old-growth forests in northern Ari- +.~%BGSTQFF - zona occur on steep slopes or in roadless can- yons.

ST. JOHNS’ 0 METHODS We located Spotted Owls by imitating their vocalizations and then listening for a response l . . (Forsman 1983). Most surveys were conducted PHOENIX0 . :* by stopping to call and listen for owls at calling 3 SBFFORDl stations spaced every 0.3-0.8 km along forest Southern Arizono roads. We remained at these calling stations for 15 min or until a Spotted Owl responded. In roadless areas we conducted surveys by hiking ridgetops or canyon bottoms and calling every 30-40 sec. Surveys were concentrated in forests and canyonlands after initial efforts to locate F’IGURE 1. Map of Arizona showinggeographic re- Spotted Owls outside of such areas failed. All gionsrecognized (northern and southernArizona) and surveys were conducted on calm nights between 160 locationswhere Spotted Owls werefound during thestudy. Also shown are two locations in theHualapai March and September, when Spotted Owls are Mountains(indicated by triangles)where Spotted Owls most responsive (Forsman et al. 1984). Surveys wereheard in 1978-1979,but werenot relocateddur- were conducted from 1984-l 988, with most oc- ing the study. curring in 1985. Most areas were surveyed only once. As a result, we undoubtedly failed to locate owls in some areas where they occurred. vial valleys containing desert vegetation types. We mapped nocturnal owl locations based on These mountains are dominated by mixed-co- a compassbearing and estimated distance to the nifer forests at high elevations. Ponderosa pine calling owl. Accuracy of this method decreased forests occur below the mixed-conifer, but are as distance to the owl increased. Consequently, limited in extent and not nearly as predominant we revisited areas by day to locate roosting owls as in northern Arizona. Below the ponderosapine when possible. Roosting owls were located by belt, extensive Madrean pine-oak forests occur calling during the day in areas where owls were (Brown 1982). These forestscontain an overstory heard at night, then homing in on a responding of Chihuahua (P. leiophylla), Apache (P. engel- owl and locating it visually. Owl locations less mannig, ponderosa,and southwesternwhite pine than 2 km apart were assumed to represent the (P. strobijknis), with an understory ofevergreen same pair unless owls could be heard in both hardwoods(Brown 1982). This forestis thus quite areas nearly simultaneously or located roosting different from the ponderosa pine-Gambel oak in both areas during the same day. This as- forests of northern Arizona. Below the pine-oak sumption may have caused us to underestimate belt, encinal woodlands of low-growing ever- the number of owls located. green oaks (Quercus spp.) are dominant. These We used roosting locations to assesshabitat woodlands are sometimes extremely dense, and use, since owls may move long distancesat night replace the pinyon-juniper woodlands found at in responseto calls (R. J. GutiCrrez, pers.comm.). lower elevations in northern Arizona. We assignedeach owl location to a broad forest Land-use history differs between regions. The type, based on a visual inspection of the area mountains of southern Arizona are managed pri- occupied by a roosting owl. Where roosting owls marily for range, watershed, and recreational could not be located or time constraints pre- purposes,and timber harvest has not been a ma- vented revisiting an area by day, forest type was jor factor in altering vegetation patterns. In con- classified as unknown. SPOTTED OWL DISTRIBUTION 351

Six forest types were recognized, based on roost tree in each cardinal direction, then aver- speciescomposition. Spruce-fir forest was dom- aged. inated by Engelmann spruce(Picea engelmannii) Information on land ownership of areas oc- and/or subalpine fir (Abieslasiocarpa), while cupied by Spotted Owls was obtained from U.S. mixed-conifer forest was dominated by Douglas Geological Survey topographic maps. Informa- fir and/or white fir, often with a prominent com- tion on management “status” of occupied lands ponent of pines (Pinusspp.) (Moir and Ludwig was obtained from U.S. Forest Service biologists. 1979). Forestswith > 50% ofoverstory treescon- Six status categorieswere recognized, based on sisting of ponderosa pine were classifiedas pon- the amount of future habitat protection offered. derosa pine forest (after Old-growth Definition Active timber saleswere defined as areas where Task Group 1986). Similarly, forestswhere > 50% timber harvest occurred during the course of the of overstory trees consisted of Apache and/or study (1984-l 988). Planned timber sale referred Chihuahua pines, with an understory of ever- to areas where harvest was planned within the green hardwoods,were classifiedas pine-oak for- next 5 years. This status could change at any est. Forestsdominated by various evergreenoaks time. Available timber lands were areasthat were were classified as evergreen oak forest, while open to harvest,but whereno harvestwas planned woodlands dominated by pinyon pines (Pinus within the next 5 years. Reserved lands included spp.) and junipers (Juniperusspp.) were classified National Park Service lands, as well as National as pinyon-juniper woodland. Within these forest Forest lands classified as wilderness, primitive, types, deciduous riparian forests or Arizona cy- or researchnatural areas.Private referredto lands press (Cupressusarizonica) forests sometimes in private ownership. occurred along canyon bottoms. Due to the lim- ited extent of such habitats, owls occurring in RESULTS these habitats were assignedto the surrounding forest type. DISTRIBUTION We surveyed extensive areas of potential hab- Spotted Owls were found at 160 locations during itat throughout the state. Forest types were often the study (Fig. l), including pairs at 77 sites and patchy within the areas surveyed, and effective single individuals at 83 sites. Repeated sampling calling distance varied with topography, vege- would probably have revealed pairs at many of tation, and weather conditions. As a result, we the latter sites (Forsman et al. 1984). Owls were were unable to determine the amount of each widely but patchily distributed in Arizona, being forest type surveyed. Therefore, the data pre- found in all but the arid southwesternportion of sented describe observed patterns of habitat the state.Owls were located only in forestedhigh- “use,” rather than habitat “selection” in the sense lands, at elevations ranging from 1,125 to 2,930 of use vs. availability. m, and their distribution reflected the availabil- At each roost site, we noted whether or not ity of such areas. timber harvest had occurred in the area. We re- In southern Arizona, we found owls at 84 sites. ferred to areas where harvest had not occurred Owls were found in the Atascosa(Pajarito), Santa as unloggedforest, rather than old-growth forest, Rita, Santa Catalina, Patagonia, Whetstone, Ga- since we lacked data on stand agefor many areas. liuro, Huachuca, Chiricahua, Pinaleno, Super- Most such stands appeared to have some or all stition, , Mazatzal, and Bradshaw of the characteristicslisted in Old-growth Defi- mountains. We were unable to locate owls in the nition Task Group (1986) as being diagnostic of basins and valleys between these ranges. Several old-growth forests, however. other mountain ranges in this region were not We measured selected site characteristics at surveyed, and Spotted Owls may be present in many roost sites (after Solis 1983). Only two some or all of these ranges. characteristics are discussed here; others were In northern Arizona (n = 76 sites), concentra- summarized in Ganey (1988). Percent slope was tions of owls were found along the Mogollon measuredwith a clinometer. Two measurements Rim, in the White Mountains, and on the vol- were averaged, one taken upslope and one taken canic peaks near Flagstaff. Owls were located at downslope from the roost. Percent canopy clo- scattered sites on the and the sure was measuredwith a spherical densiometer. Navajo Reservation. There are historic records Four measurements were taken 5 m from the from the Mountains in northwestern 358 JOSEPH L. GANEY AND RUSSELL P. BALDA

Arizona, but we were unable to locate owls there this forest type. Most owls were located in un- during the study. Many areaswere not surveyed, logged forests in southern Arizona. In the few and Spotted Owls are undoubtedly more wide- caseswhere timber harvest had occurred, it con- spread than our data indicate. sisted of light overstory removal through selec- tive logging. SPACING OF PAIRS In northern Arizona, Spotted Owls were found We did not have sufficient data to estimate den- at elevations ranging from 1,525-2,925 m, and sities of Spotted Owls. We did estimate nearest- inhabited only two major forest types (Fig. 2). neighbor distancesfor two areas in northern Ar- Most owls in northern Arizona (67%) were found izona where we were confident we had located in mixed-conifer forest. A few owls (5%) were all resident pairs. Mean nearest-neighbor dis- located in ponderosa pine forest; none were lo- tances were 3.8 km in the cated in spruce-fir forest. Pine-oak and evergreen area (n = 7 pairs, SE = 0.42, range = 1.5-7.1 oak forests did not occur in northern Arizona km) and 3.5 km in the White Mountains of east- (Brown 1982). In general, the range of the Spot- ern Arizona (n = 6 pairs, SE = 0.12, range = ted Owl in northern Arizona appeared to coin- 2.7-6.1 km). The minimum known distance be- cide with the mixed-conifer zone between the tween two active nests in northern Arizona was ponderosa pine belt and the spruce-fir forest. 2.7 km. Nearest-neighbor distances were not Stands of unlogged forest were present at all computed for owls in southern Arizona, due to but two of the owl sites(3%) in northern Arizona. inadequate data. Pocketsof mature timber remained after harvest at both sites, and these pockets of closed canopy HABITAT USE (> 80%) forest were used by roosting owls. Most Spotted Owls were located in deep canyons, Becausewe made no attempt to quantify the particularly at the lower end of the owl’s eleva- amount of each forest type surveyed, a potential tional range. At elevations above 2,300 m owls for bias existed in analysis of habitats occupied. appeared to be less dependent on deep canyons, This potential was difficult to evaluate in south- and were found on mountain slopesas well. Owls em Arizona, but was not suspectedto seriously were found in several forest types, ranging from bias the results presented here. All of the avail- coniferous forests to evergreen oak forest and able forest types were surveyed for owls, owls associateddeciduous riparian forests.Owls were were located in all forest types from the evergreen alsolocated in canyonscontaining extensiverocky oak belt upwards, and we have no reasons to cliffs with potholes and caves; these structures suspectthat the pattern of occupancy is greatly were used for both roosting and nesting when different from the pattern presented here. available. In northern Arizona, a mosaic of loggedridge- In southern Arizona, owls were found at ele- tops and unlogged canyons occurred, and most vations ranging from 1,125-2,930 m. Habitat surveys were conducted from roads through se- use was more variable in this region than in lectively-logged ponderosa pine forest on ridge- northern Arizona (Fig. 2). At elevations below tops. Since owl responseis likely to decreasewith 1,300 m owls were found in steep canyons con- distance, this should have created a bias toward taining cliffs and stands of evergreen oaks, Mex- location of owls in loggedponderosa pine forest. ican pinyon (P. cembroides),and broadleaved Thus, the fact that most owls in northern Arizona riparian trees. Above 1,800 m owls were found were found in unloggedmixed-conifer forest was primarily in mixed-conifer and pine-oak forests. unlikely to be due to survey bias. Mid-elevation sites were variable, and included Despite the range of forest types occupied, cer- Arizona cypressforests as well as all of the forest tain features were shared by most sites. Most types mentioned above. The lower limit of Spot- owls were found on steep slopes(X = 56%, SE = ted Owl habitat appeared to coincide with the 6.2, n = 44) containing unlogged forests and/or lower limit of the evergreen oak belt, while there rocky cliffs. The relative amount of forest and did not appear to be a well-defined upper limit cliff varied among sites. At one extreme owls to Spotted Owl range in southern Arizona. A were located in canyons containing extensive for- possible exception to this pattern was the Pina- ests and little or no cliff habitat. At the other leno Mountains, where spruce-fir forest occurred extreme owls were located in canyons with prom- at the upper elevations. No owls were found in inent cliffs where forest habitat was largely re- SPOTTED OWL DISTRIBUTION 359

stricted to a narrow belt along the canyon bot- NORTHERN ARIZONA (N q 76) tom. Many siteswere intermediate between these extremes,containing cliffs and rock outcropsand extensiveforest tracts. Habitat diversity was often high, with different forest types forming a com- plex mosaic. Owls generally roosted on shaded cliffs (n = 5) or in unlogged stands with high canopy closure (X = 86%, SE = 1.3, y1= 39). Canopy layering was well-developed in mixed- conifer and pine-oak forests, and most owls roosted in these types. Canopy layering was not well-developed in evergreen oak and ponderosa pine forests,and fewer owls roosted in these for- 5.3 % est types (Fig. 2).

LAND OWNERSHIP OF SITES WHERE OWLS WERE LOCATED SOUTHERN ARIZONA (N = 84) Most owls (89%) were located on lands admin- istered by the U.S. Forest Service, with the re- mainder located on Department of Defense, In- Ponderoso Pin dian Reservation, National Park Service, Bureau 6 % of Land Management, and private lands. This pattern was partly due to the fact that survey effort was greater on U.S. Forest Service lands, but there is no question that the types of habitats Evergreen Oak 10.7 % occupied by Spotted Owls in Arizona are con- centrated on these lands. Few owls were located on reserved lands in Pine-ook Arizona. In northern Arizona, where most tim- 22 6 % ber harvest occurs, 54% of the 76 known owl FIGURE 2. Forest typesused for roostingby Spotted sites were in active or planned timber sales. Owls in northern (n = 76 sites) and southern (n = 84 sites)Arizona. Geographicregions and forest types are Another 35.5% were on available timber lands defined in the text. where no timber harvest was planned in the next 5 years. Only 10.5% of the known sites were on reserved lands. was sufficiently accurate to allow location of the original observation. Spotted Owls were found SITE OCCUPANCY AND at 11 (73%) of these sites. No owls were located POPULATION TRENDS at the remaining four sites (27%) despite inten- Site occupancy was monitored by checking 44 sive searching. Two of these sites were in areas known owl sites at l- to 3-year intervals to de- formerly occupied by extensive riparian forests termine if suchsites were continuously occupied. (Bendire 1892) that had subsequently been con- One or more owls were relocated at 42 of these verted to arid desert. At the third site, the owls sites in one or more years. At the other two sites, formerly nested in a rocky grotto that subse- occupancy was uncertain because survey effort quently became a heavily used recreational area. was limited. The fourth site had undergone no obvious hab- Site tenacity was monitored for eight adult owls itat alteration and appeared to contain suitable radio-tagged in northern Arizona during the habitat. summer of 1986. Seven of these owls still oc- cupied the same home ranges in August 1987. DISCUSSION The eighth owl died in November 1986, while Spotted Owls appear to be most common in still on its home range. mountains and canyons containing mixed-co- To evaluate population trends, we resurveyed nifer, pine-oak, and evergreen oak forests. They 15 historic Spotted Owl sites where information are also found in ponderosapine forest and rocky 360 JOSEPH L. GANEY AND RUSSELL P. BALDA canyonlands, and we cannot rule out the possi- potential for loss of Spotted Owl habitat in this bility that they occur occasionally in other hab- region. itats. Owl pairs occurred at intervals of 3-4 km Habitat loss due to timber harvest has been in suitable habitat in northern Arizona. Marshall blamed for declining Spotted Owl populations (1957) estimated that pairs occurred every 1.6- along the west coast (Gould 1977, Forsman et 3.2 km in the mountains of southern Arizona, al. 1984). Population trends are difficult to eval- suggestingthat densities may vary among re- uate in Arizona, due to the short duration of this gions. More surveys and a better understanding study and the lack of historic information. The of Spotted Owl habitat requirements and den- fact that owls are now found primarily in rem- sities will be required to arrive at an accurate nant stands of unlogged forest on steep slopes estimate of the number of Spotted Owls in Ar- suggeststhat timber harvest may have reduced izona. the amount of suitable habitat. Habitat loss has Spotted Owls are most common in unlogged certainly occurred where shady low-elevation ri- old-growth forests in the Pacific Northwest parian forestshave been eliminated, and we were (Gould 1977, Marcot and Gardetto 1980, Fors- unable to locate Spotted Owls at 27% of the his- man et al. 1984). Most Spotted Owls in Arizona toric sites resurveyed. Thus, a decline in Spotted were also found in unloggedforests, often in steep Owl numbers may already have occurred in Ar- canyons. In the few caseswhere owls were lo- izona. cated in selectively-logged forests, they roosted Habitat loss due to timber harvest could have in remnant unloggedstands. This associationbe- severe consequencesfor Mexican Spotted Owls. tween Spotted Owls, steep canyons, and un- This owl is already patchily distributed. Further logged forestsalso appearsto hold in New Mex- fragmentation of suitable habitat could disrupt ico (Johnsonand Johnson 1985, Skaggsand Raitt dispersal patterns, increase isolation of subpop- 1988). ulations, and reduce effective population size, Mexican Spotted Owls do not appear to de- thus increasing the likelihood of local extinction pend on old-growth foreststo the same extent as (Dawson et al. 1987, Lande and Barrowclough northern Spotted Owls, however, as they are 1987). Unless land managers act quickly to pro- sometimes found in rocky canyons with little tect Spotted Owl habitat, future management op- forest habitat (Kertell 1977, Wagner et al. 1982, tions could be lost, and Mexican Spotted Owls Johnson and Johnson 1985, this study). Barrows could be reduced in numbers or eliminated from (198 1) suggestedthat Spotted Owls are intolerant large portions of their present range. ofhigh temperaturesand may require closedcan- opy forests for protection from heat. This may ACKNOWLEDGMENTS explain the ability of owls in Arizona to inhabit We heartily thank the many professionalbiologists and deep canyons lacking extensive forests. In such private citizens who assistedwith surveysor provided cases the cliffs and caves present may provide information about owl locations. We especiallythank the necessary refuges from high daytime tem- G. A. Goodwin for moral and logisticsupport through- peratures. out the study. Thanks also to G. C. Bateman and C. Mixed-conifer forest appeared to be an im- N. Slobodchikofffor their critical input. Comments by R. J. Gutierrez and an anonymous reviewer greatly portant forest type for Mexican Spotted Owls. improved the paper. This study was largely supported Fifty-one percent of all owls located in Arizona by the U.S. Forest Service, Southwestern Region, were found in mixed-conifer forest, even though through a cooperative agreement with the Arizona this forest type covers only 3% of Arizona (Moir Game and Fish Department, Nongame Branch. Special thanks to E. L. Fisher and R. L. Glinski for adminis- and Ludwig 1979). In New Mexico, Skaggsand tering this agreement.Additional funding was provid- Raitt (198 8) found significantly higher densities ed b; the National Wildlife Federation, the Arizona of Spotted Owls in mixed-conifer forest than in Wildlife Foundation. and the Arizona Wildlife Fed- either ponderosa pine forest or pinyon-juniper eration woodland. Spotted Owls in northern Arizona were found primarily in unlogged mixed-conifer LITERATURE CITED forest, and may require such forestswhere rocky BARROWS,C. 1981. Roost selectionby Spotted Owls: canyons are lacking. Since 89% of northern Ar- an adaptation to heat stress.Condor 83:302-309. izona owl sites were located on lands available BENDIRE, C. E. 1892. Life histories of North Amer- for timber harvest, there appears to be a high ican birds. U.S. Natl. Mus. Spec. Bull. No. 1. SPOTTED OWL DISTRIBUTION 361

BROWN,D. E. [ED.] 1982. Biotic communities of the MARSHALL,J. T., JR. 1957. Birds of the pine-oak American southwest-United States and Mexico. woodland in southernArizona and adjacent Mex- Desert Plants 4: l-4. ice. Pacific Coast Avifauna 32178-19: DAWSON,W. R., J. D. LIGON, J. R. MURPHY, J. P. MOIR. W. H.. AND J. A. LUDWIG. 1979. A classifi- MYERS, D. SIMBERLOFF,AND J. VERNER. 1987. cation of spruce-firand mixed-conifer habitat types Report of the Scientific Advisory Panel on the of Arizona and New Mexico. USDA For. Serv. Spotted Owl. Condor 89:205-229. Res. Pap. RM-207. Rocky Mtn. Res. Station. Fort FORSMAN,E. D. 1983. Methods and materials for Collins, CO. locating and studying Spotted Owls. USDA For. OLD-GROWTHDEFXXTION TASK GROUP. 1986. Inter- Serv. Gen. Tech. Rept. PNW- 162. PacificNW Res. im definitions for old-growth Douglas-fir and Station. Portland, OR. mixed-conifer forestsin the Pacific Northwest and FORSMAN,E. D., E. C. MESLOW,AND H. M. WIGHT. California. USDA For. Serv. Res. Note PNW-447. 1984. Distribution and biology of the Spotted Pacific NW Res. Station. Portland, OR. Owl in Oregon. Wildl. Monogr. 87:1-64. SKAGGS,R. W. 1988. Status of the Spotted Owl in GANEY,J. L. 1988. Distribution and habitat ecology southernNew Mexico: 1900-l 987. Contract No. of Mexican Spotted Owls in Arizona. MSthesis. 519-75-02. New Mexico Dep. Game and Fish. Northern Arizona Univ., Flagstaff. Santa Fe, NM. GOULD,G. I. 1977. Distribution of the Spotted Owl SKAGGS,R. W., AND R. J. RAITT. 1988. A Spotted in California. West. Birds 8: 13l-146. Owl inventory on the Lincoln National Forest Sac- JOHNSON,J. A., ANDT. H. JOHNSON.1985. The status ramento Division: 1988. Contract No. 5-5 16.6- of the Spotted Owl in northern New Mexico. Con- 76-17. New Mexico Dep. Game and Fish. Santa tract No. 516.6-73-03. New Mexico Dep. Game Fe, NM. and Fish. Santa Fe, NM. SOLIS,D. M., JR. 1983. Summer habitat ecology of KERTELL.K. 1977. The Snotted Owl at Zion National Spotted Owls in northwestern California. Park, Utah. West. Birds 8:147-150. M.S.thesis. Humboldt State Univ., Arcata, CA. LANDE,R., AND G. F. BARROWCLOUGH.1987. Effec- WAGNER,P. W., C. D. MARTI,AND T. C. BONER. 1982. tive population size, genetic variation, and their Food of the Spotted Owl in Utah. Raptor Res. 16: use in population management, p. 87-123. In M. 27-28. E. Soule [ed.], Viable populations for conserva- WEBB,B. 1983. Distribution and nesting require- tion. Cambridge Univ. Press.,New York. ments of montane forest owls in Colorado. IV. MARCOT,B. G.. AND J. GARDETTO. 1980. Status of Spotted Owl (5X.x occidentalis).Colo. Field Or- the Spotted Owl in Six Rivers National Forest, nithol. 17:2-8. California. West. Birds 11:79-87.