Distribution and Habitat Use of Mexican Spotted Owls in Arizona’
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The Condor 91:355-361 0 The CooperOrnithological Society 1989 DISTRIBUTION AND HABITAT USE OF MEXICAN SPOTTED OWLS IN ARIZONA’ 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