Using terrestrial ecosystem survey data to identify potential habitat for the Mexican spotted owl on National Forest System lands: a pilot study

Ganey, Joseph L.; Benoit, Mary Ann. 2002. Using terrestrial ecosystem survey data to identify potential habitat for the Mexican spotted owl on National Forest System lands: a pilot study. Gen. Tech. Rep. RMRS-GTR-86. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. 25 p. We assessed the usefulness of Terrestrial Ecosystem Survey (TES) data as a means of identifying habitat for the Mexican spotted owl (Strix occidentalis lucida) in three National Forests in Arizona. This spatial data set incorporates information on soils, vegetation, and climatic conditions in defining a set of ecological “map units” showing potential vegetation. We used three separate data sets consisting of spotted owl locations resulting from: (1) U.S. Forest Service (USFS) surveys; (2) mark-recapture sampling of 12 randomly selected “quadrats” ranging from 40 to 76 km, conducted in conjunction with population monitoring efforts; and (3) monitoring of radiomarked owls in four study areas. For each data set and National Forest, we overlaid owl locations on geographical information system (GIS) coverages of TES map units and summarized data on relative use patterns. Using standardized criteria specific to each data set, we identified subsets of map units strongly associated with owl use based on that data set and assessed subset consistency among data sets. All data sets identified a subset of map units as associated with owl use. Most map units identified by quadrat or radiotelemetry data also were identified by the more extensive but less detailed USFS survey data, but the converse was not true. Map units identified as associated with owl use generally consisted of mixedconifer or pine-oak forest, and those units most strongly associated with owl use typically occurred on steep slopes containing rock outcrops. These ecological characteristics are consistent with existing knowledge of Mexican spotted owl habitat. We concluded that: (1) TES data was useful in identifying areas associated with owl use; and (2) with certain caveats, USFS survey data can be used in the absence of more detailed data sets. We also present an objective technique that can be used to identify a subset of owl-associated map units using flexible criteria that can be tailored to meet different objectives.