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Mexican Spotted Owls in Canyonlands of the Colorado Plateau


by
David W. Willey
National Biological Service
In response to perceived threats to critical nesting habitat and lack of adequate protective regulations, the Mexican spotted owl (Strix occidentalis lucida) was officially listed as a threatened species under the Endangered Species Act in 1993 (Federal Register 1993). Limited information is available on the distribution of Mexican spotted owls inhabiting arid canyonlands throughout the southwestern United States (Ganey and Balda 1989). Though widely distributed, the Mexican spotted owl apparently occurs in isolated populations restricted to habitat islands (Fig. 1). Here I report findings from spotted owl surveys conducted throughout the northwest portion of the Colorado Plateau in Utah.

Fig. 1. Distribution of Mexican spotted owls in the southwestern United States.
Mexican spotted owls (Strix occidentalis lucida) roosted in canyonlands in southern Utah. Courtesy Steve Howe, Mills Publishing, Inc.©
The Colorado Plateau Physiographic Province consists of extensive sandstone canyons interspersed by eroded valleys, upwarped plateaus, and isolated mountain ranges (Thornbury 1965). Prolonged erosional dissection produced a maze of complex watersheds within the Colorado Plateau region (Youngblood and Mauk 1985). Agency lands encompassed by the Colorado Plateau include extensive U.S. Department of Agriculture national forests and U.S. Department of the Interior Bureau of Land Management (BLM) areas, seven National Park Service national parks, two national recreation areas, several national monuments, and state-administered lands, all in the Four Corners region (Arizona, New Mexico, Colorado, and Utah) of the southwestern United States.
These lands may function as biological refugia, providing dispersal corridors and habitat islands joining occupied and potentially suitable spotted owl habitat. In the Four Corners region, spotted owls are associated with rocky canyon terrain (i.e., canyonlands) and could be negatively affected by such activities as timber harvesting, mining, and recreation (Ganey 1988). Long-term study of spotted owl distribution and habitat use is necessary to provide information on the potential effects of human activities and to develop ecologically based conservation plans (Gutiérrez 1989).

Surveys
Information on Mexican spotted owl distribution within canyonlands of the Colorado Plateau was gathered by using published species accounts and conducting field surveys.
During the field surveys, individuals and pairs of owls were located by imitating their calls with the human voice or using taped broadcasts of their calls to elicit a response from the owls (Forsman 1983). The surveys were conducted during each breeding season (1 April-31 August) from 1989 through 1993. Target areas were visited four times during the breeding season to search for owls. Spotted owl callers ("hooters") conducted searches by "hooting" at stations located on night-time survey routes placed within search areas. Hooters conducted daytime visits to sites where spotted owls were heard at night in order to find nests and count young.

Historical Records
Historical records of Mexican spotted owls on the Colorado Plateau date back to the 1920's (McDonald et al. 1990). The earliest record in the canyonlands was from Zion National Park in June 1928. A single owl was reported in August 1957, in Davis Gulch, a tributary of the Escalante River in southern Utah. Three birds were seen in July 1958, in a small side canyon of Glen Canyon National Recreation Area, and another was observed at the mouth of the Escalante River. The most northerly occurrence of a spotted owl on the Colorado Plateau was recorded in September 1958, in the Book Cliff Mountains. Spotted owls have been observed occasionally since the early 1970's throughout the canyonlands of southern Utah. Kertell (1977) detected spotted owls at six locations in Zion National Park in the early 1970's. The species accounts suggest that spotted owls were widely dispersed throughout the canyonlands of the Colorado Plateau, especially in deeply eroded sandstone gorges.

Field Survey Results

About 202,500 ha (500,000 acres) were surveyed from 1990 to 1993 on U.S. Forest Service lands, and more than 483 km (300 mi) of BLM canyons were surveyed from 1991 to 1993. Surveys were also conducted in portions of Grand Canyon, Capitol Reef, Canyonlands, and Zion national parks, as well as Natural Bridges and Navajo national monuments. Seventy-six spotted owls (26 pairs and 24 single adults) were detected at 50 locations: 6 on U.S. Forest Service lands, 12 on BLM lands, 1 on state lands, and 31 on National Park Service lands (Fig. 2).

Fig. 2. Distribution of Mexican spotted owls in canyonlands of southern Utah, representing the northwest portion of the Colorado Plateau Physiographic Province.
Groups or subpopulations of owls were distributed among several landscape areas spread across the northwest portion of the Colorado Plateau including the greater Zion National Park area; the greater Capitol Reef area; the Dirty Devil River watershed; Canyonlands National Park; and near Elk Ridge and Dark Canyon on the Manti LaSal National Forest.
Mexican spotted owls were widely distributed and appeared coincident with canyon habitat. Canyon habitats on the Colorado Plateau are discontinuous and reflect the naturally fragmented topographic conditions of the plateau region. This patchy landscape could explain the patchy locations of surveyed spotted owls. A study conducted in Zion National Park found owls nesting and roosting in humid, narrow canyons with dense understories (Rinkevich 1991). Since many owls on the Colorado Plateau were found in similar habitat, the owls may be selecting these canyons because of their unique habitat features: large cliffs that provide escape cover to avoid predation, shaded roost sites to avoid high summer temperatures, patches of forest vegetation, and availability of suitable prey.
Relatively few owls were found in the canyonlands area compared with forest sites in Arizona and New Mexico; thus, canyonland owl sites may need special protection. Further surveys should be conducted across USDI lands to more accurately assess distribution and habitat of spotted owls.
For further information:
David W. Willey
National Biological Service
Colorado Plateau Research Station
Northern Arizona University
Box 5640
Flagstaff, AZ 86011
References
Federal Register. 1993. Endangered and threatened wildlife and plants: final rule to list the Mexican spotted owl as a threatened species. Federal Register 58:14248-14271.

Forsman, E.D. 1983. Methods and materials for locating and studying spotted owls. Gen. Tech. Rep. PNW-162. U.S. Forest Service, Pacific Northwest Forest and Range Experiment Station, Portland, OR. 8 pp.

Ganey, J.L. 1988. Distribution and habitat ecology of Mexican spotted owls in Arizona. M.S. thesis, Northern Arizona University, Flagstaff. 229 pp.

Ganey, J.L., and R.P. Balda. 1989. Distribution and habitat use of Mexican spotted owls in Arizona. Condor 91:355-361.

Gutiérrez, R.J. 1989. Distribution and abundance of spotted owls in Zion National Park. National Park Service, Order PX-1200-9-C820. 69 pp.

 Kertell, K. 1977. The spotted owl at Zion National Park. Western Birds 8:147-150.

McDonald, C.B., J. Andersen, J.C. Lewis, R. Mesta, A. Ratzliff, T.J. Tibbots, and S.O. Williams III. 1990. Mexican spotted owl status review. U.S. Fish and Wildlife Service, Endangered Species Rep. 20. Alberquerque, NM. 85 pp.

Rinkevich, S.E. 1991. Distribution and habitat characteristics of Mexican spotted owls in Zion National Park, Utah. M.S. thesis, Humboldt State University, Arcata, CA. 62 pp.

Thornbury, W. 1965. Regional geomorphology of the United States. John Wiley and Sons, New York. 609 pp.

Youngblood, A.P., and R.L. Mauk. 1985. Coniferous forest habitat types of central and southern Utah. Gen. Tech. Rep. INT-187. U.S. Forest Service, Intermountain Forest and Range Experiment Station, Ogden, UT. 89 pp.


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