Rainwater Basin Joint Venture Rainwater Basin JV GIS Lab 2550 N Diers Ave Suite L 203 W 2nd St. second floor Grand Island, NE 68801 Grand Island, NE 68801 (308) 382-8112 (308) 382-6468 x33 Prairie Dog and Burrowing Owl Habitat Analysis throughout Nebraska By the Rainwater Basin Joint Venture Andy Bishop1, Laura Achterberg1, Roger Grosse1, Ele Nugent1, Christopher Jorgensen1,2 1Rainwater Basin Joint Venture, 2550 North Diers Ave, Grand Island, NE 68801 2Nebraska Cooperative Fish and Wildlife Research Unit, 422 Hardin Hall, 3310 Holdrege Street, Lincoln, NE 68583 This work was funded in part by the Nebraska Game and Parks Commission through a Department of Energy grant to the Western Governors' Association [DOE Grant # DE-OE0000422 "Resource Assessment and Interconnection-Level Transmission Analysis and Planning (for the Western Interconnect)"] A special thanks to Mike Fritz, Joel Jorgensen, Jeff Lusk, Rick Schneider, Rachel Simpson, and Kristal Stoner for providing comments and support during the project. Introduction The following project sought to identify potential available habitat for burrowing owls in Nebraska. Burrowing owls are considered a Tier 1 at-risk species (i.e., a species globally or nationally most at risk of extinction) by the Nebraska Game and Parks Commission (NGPC; Schneider et al. 2005). We developed a conceptually based, spatially explicit habitat suitability index to determine the remaining suitable habitat for burrowing owls in Nebraska. Model development was based on a previous modeling exercise geared towards identifying suitable habitat for black-tailed prairie dogs in Nebraska, which was performed by the GIS Workshop, Inc. for the NGPC in 2003. Given that burrowing owls form a symbiotic relationship with prairie dogs and their habitat, and often make use of prairie dog burrows for nesting, the previous prairie dog model was adapted and updated using current data to locate areas suitable for burrowing owls. Methods We created the burrowing owl habitat suitability index using six GIS raster layers for inputs, including: soils range site, soil psamment, depth to water table, slope, vegetation landcover, and wetlands/hydrology. Habitat suitability values were assigned to each of the six GIS raster layers based on NGPC biologists’ recommendations, utilizing a 3-teir classification scheme. Suitable 1 habitat was considered the highest priority and was assigned a value of 2, while marginally suitable habitat was assigned a value of 1, and unsuitable habitat was assigned a value of 255. Individual Layer Suitability Score Habitat Suitability 2 Suitable 1 Marginal 255 Unsuitable The values for each of the six suitability layers were added together. However, if any pixel within the raster layer was classified as unsuitable (i.e., a habitat suitability value of 255), the combined habitat index for that specific area was required to be “unsuitable”. The possible output raster values for the habitat suitability index were as follows: Final Output Suitability Score Habitat Suitability 12 Highly Suitable 11 Very Suitable 10 Suitable 8-9 Marginal 0 Unsuitable Soils We derived the soil data from the Soil Survey Geographic Database 2.2 (SSURGO), which is highly considered to be the most detailed level of geospatially referenced soil data available through the Natural Resources Conservation Service (NRCS). SSURGO data layers were created by following national standards. Soils were digitized using a line segment (i.e., vector) format following the NRCS digitizing guidelines. SSURGO data are distributed as a complete geographic coverage for a specified soils survey area. Mapping scales generally range from 1:12,000 to 1:63,360, which are designed for use by landowners, townships, and county natural resource planning and management. SSURGO is linked to a National Soil Information System (NASIS) attribute database, which provides the proportionate extent of the component soils and their properties for each map unit. One to three soil components are assigned to each SSURGO map unit. For this analysis, we downloaded SSURGO data on a county-by-county basis from Soil Data Viewer 5.2 using ArcGIS 9.2. We merged multiple data layers together into a single shapefile to provide a statewide coverage. Each polygon in the dataset represented a single SSURGO map unit. The attribute “MUKEY” was used to associate the map unit with the soil characteristics information from the related tables which are accessible through the NRCS’s Soil Data Viewer Extension for ArcGIS. We extracted the soil map unit name and the range site name from the Soil Data Viewer. Specifically, the soil map unit name provides the soil series name, which is a brief descriptive name for the soil and non-soil areas delineated in a soil survey. The range site 2 name is a functional name identifier that was developed by the NRCS to uniquely identify each map unit in a particular soil survey area. The rangeland ecological site name provides a general description of a particular ecological site (e.g., "Loamy Upland). More specifically, an "ecological site" is the product of all the environmental factors responsible for its development. It has characteristic soils that have developed over time, a characteristic hydrology (particularly infiltration and runoff that has developed over time) and a characteristic plant community. The vegetation community, soils, and hydrology are all interrelated. The plant community on an ecological site is typified by an association of species that differs from other ecological sites in the kind and/or proportion of species, or in total production. A single range site name includes many different soil types while, conversely, a single soil series can have different subgroups that belong to many different range site names. Descriptions of ecological sites are provided in the Field Office Technical Guide, which is available in local offices of NRCS. Descriptions of those displayed in this map and summary table may also be accessed through the Ecological Site Assessment tab in Web Soil Survey. Burrowing owls are known to occupy burrows 200 cm below the soil surface in Washington (Conway et al. 2006) and 69 cm in Oklahoma (Butts and Lewis 1982). We took the average of these two estimates, establishing burrow preference of 136 cm below the soil surface. A generous leeway in marginal suitability was given for depth to impervious layers, lithic contact, and depth to water table. Table 1. Habitat suitability classifications for burrowing owl assigned to each soil type. The majority of suitability classifications are based on original prairie dog model created by GIS Workshop, Inc., however, certain categories have changed to reflect burrowing owl habitat preference. Range Site Name Suitability Platte Comments Suitability Choppy Sands 255 255 Sands 2 2 Sandy 2 2 Sandy Lowland 2 2 Shallow Sandy 255 255 Impervious within 20 in (50cm) Clayey 1 1 Clay Upland 2 2 Shallow water table 60 cm Clayey Overflow 1 1 Water table varies, often too high, rely on flood/pond layer Dense Clay 2 2 Impervious Shallow Clay 2 2 Impervious, Lithic contact 20cm Silty 1 1 Silty Lowland 1 1 Water table varies, rely on flood/pond layer Silty Overflow 1 1 Water table varies, rely on flood/pond layer Loamy 1 1 Loamy Upland 1 1 Loamy Terrace 1 1 Water table varies, rely on flood/pond layer Loamy Overflow 1 1 Water table varies, rely on flood/pond layer Loamy Lowland 1 1 Water table varies, rely on flood/pond layer 3 Limy Upland 1 1 Shallow Limy 2 2 Impervious, Lithic contact 10-20in (25-50cm) Shallow 255 255 Clean Gravel 10-20 in from surface Shallow to Gravel 2 2 Consider 255 Gravelly 2 2 Gravelly Hills 2 2 Closed Upland Depression 255 255 Flooded/Ponded No Site 2 2 Panspots 1 1 Thin Breaks 2 2 Loess Breaks 2 2 Thin Loess 2 2 Thin Upland 2 2 Wet Land 255 *2 Subirrigated 255 *2 High Water Table 61cm + Wet Subirrigated 255 *2 Saline Subirrigated 255 *2 Saline Lowland 2 2 Saline Upland 2 2 Impenetrable ground Udarents/Ustorthents 255 255 Cut and Fill Urban Land 255 255 Mine or Gravel Pit 255 255 * Areas within Platte River Valley affected by the adjusted water table suitability values Depth to Water Table The water table, or saturation zone, is highly variable within and among years, and therefore ranges between a minimum and maximum value over time. We estimated the upper limit of the water table based on local observations at a select number of sites by looking for evidence of a saturation zone (i.e.,redoximorphic features in the soil). We defined a water table to be any area that remained saturated for longer than a month. The soil saturation zone is recorded as three separate values in SSURGO, a minimum, maximum, and representative value. The minimum and maximum values indicate the range, and thus, the potential variation within the water table over time. For this analysis, we focused solely on the representative value, which is the expected depth of the water table at any given time. Given that burrows cannot persist below the water table, we specified suitability for soils with a representative water table greater than 121 cm (~4 ft) below the surface. We also considered water tables within the upper 60 cm of the soil as unsuitable. This pertained mainly to soils with range site names of “Overflow” and “Lowland” categories. Significant high water tables also existed in “Clay Upland.” In areas with a moderate depth to the water table (i.e., 61 – 121 cm), burrowing owls may create shallower burrows if deeper sites are unavailable (Mike Fritz, NGPC, personal communication). Therefore, these sites were assigned marginal habitat suitability values. Values were assigned as follows: 4 Suitability Depth to Water Table 2 > 121 cm 1 61 – 121 cm 255 0 – 60 cm Wetlands/Hydrology Wetland and hydrological data are based on the National Wetlands Inventory (NWI) digital wetlands maps of wetland locations and types as defined by the U.S.