USING NATIONAL WETLANDS INVENTORY MAPS TO QUANTIFY WHOOPING CRANESTOPOVER HABITAT IN OKLAHOMA

Three stratified random samples of the 416 National Wetland Inventory (NWI) maps within the western Oklahoma portion of the Wood Buffalo-Aransas whooping crane (Grus americana) migration corridor were used to evaluate the availability of wetland roost sites. Wetlands were eliminated as potential roosts if visibility was obscured by vegetation or slope, or if certain human activities occurred within 100-800 m. Thirty percent of all wetlands >0.04 ha passed map review, but only 7% passed when ground truthed. NWI map review was a poor predictor of suitability (33 % correct) but a good predictor of unsuitability (97 % correct). Most (>75%) wetlands in western Oklahoma are man-made impoundments dug to water livestock. They are generally small « 1 ha), dammed, in steep drainages, and tree-lined. Most stock ponds do not meet the horizontal visibility requirements of roosting whooping cranes. Map review of wetlands > I ha (no randomized field review) suggests that 2-4 suitable crane roosts are available per 100 km2 in the migration corridor in Oklahoma. Three major rivers and approximately 20 large reservoirs (> 16 ha) provide the best roost sites. Without adequate ground truthing, review of NWI maps, even when supplemented by Soil Conservation Service photo maps, overestimate suitable roost sites, especially in areas where rainfall is sufficient to support woody vegetation > 1 m in height. Key Wordr: Grus americana, habitat, maps, migration, Oklahoma, whooping crane The whooping crane is one of the best known endangered species and has received considerable attention during the past half century. In the 1940's and early 1950's protection and management were concentrated on the wintering grounds at Aransas National Wildlife Refuge, Texas, then the species' only known area of use (Allen 1952). An equal emphasis on management and research occurred at Wood Buffalo National Park, Northwest Territories, Canada, after the breeding grounds were discovered there in 1954. During the 1960's and 1970's establishing a captive and an additional wild flock became integral parts of management efforts (Erickson 1975, Drewien and Bizeau 1978). Since the mid-1970's there has been an increased emphasis on documenting and understanding the migration routes and stopover roosting habitat used by Wood Buffalo-Aransas whooping cranes (Lingle et a1. 1984; Howe 1987, 1989; Ward and Andcrson 1987). As information has accrued on migratory roost sites, it has been possible to develop suitability criteria and indices for non-traditional roosts (Armbruster 1990), which are dermed as sites used only a few nights (usually only 1 night) during migration (Mdvin amI Temple 1982). Cuncern about the availability of suitable roosts within the migration corridor (Lingle 1987) has prompted efforts to inventory potential roost sites. The U.S. Fish and Wildlife Service (USFWS) initiatcd its current and ongoing National Wetland Inventory (NWI) program in 1974 based on a detailed hierarchical classification system (Cowardin et a1. 1979). The goal of NWI is to provide baseline data on the physical characteristics and 62 PROC. NORTH AM. CRANE WORKSHOP 6:62-68 extent of all United States wctlands so that these diminishing habitats might be better managed (Montanari and Townsend 1977). The purpose of this study was to evaluate the utility of NWI maps, when used in conjunction with aerial photo maps and suitability criteria (Armbruster 1990), in predicting stopover roost availability for migrant whooping cranes in western Oklahoma (Fig. 1). This study was funded by the USFWS, Endangered Species Program. I thank J. C. Lewis for support and guidance throughout the project. C. J. Carley provided NWI maps and answered many questions about NWI classifications and mapping procedures. D. H. Johnson provided valuable suggestions on sampling design and aided with data analysis. Reviews by M. A. Bishop, S. P. Grcen, and J. C. Lewis markedly improved the manuscript.