Prairie Dog and Burrowing Owl Habitat Analysis throughout Nebraska: Summary

Rainwater Basin Joint Venture Report. 2012.

Andy Bishop1, Laura Achterberg1, Roger Grosse1, Ele Nugent1, and 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

Introduction For this analysis, we downloaded SSURGO data on a county by Identifying suitable habitat in the landscape for rare and elusive county basis from Soil Data Viewer 5.2 using ArcGIS 9.2. We species can assist wildlife managers in forming conservation merged multiple data layers together into a single shapefile to plans and can even facilitate new discoveries of species provide a statewide coverage. Each polygon in the dataset populations. The following project sought to identify available represented a single SSURGO map unit. We extracted the soil habitat for Burrowing Owls in Nebraska. Burrowing Owls are map unit name and the range site name from the Soil Data considered a Tier 1 at-risk species (i.e., a species globally or Viewer. nationally most at risk of extinction) by the Nebraska Game and Parks Commission (NGPC). We developed a conceptually Burrowing Owls are known to occupy burrows 200 cm below based, spatially explicit habitat suitability index to determine the the soil surface in Washington (Conway et al. 2006) and 69 cm remaining suitable habitat for Burrowing Owls in Nebraska. in Oklahoma (Butts and Lewis 1982). We took the average of Model development was based on a previous modeling exercise these two estimates, establishing burrow preference of 136 cm geared towards identifying suitable habitat for Black-tailed below the soil surface. A generous leeway in marginal Prairie Dog in Nebraska, which was performed by the GIS suitability was given for depth to impervious layers, lithic Workshop, Inc., Lincoln, Nebraska, U.S.A., for the NGPC in contact, and depth to water table. 2003. Given that Burrowing Owls form a symbiotic relationship with prairie dogs and their habitat, and often make use of prairie Depth to Water Table dog burrows for nesting, the previous prairie dog model was The water table, or saturation zone, is highly variable within and adapted and updated using current data to locate areas suitable among years, and therefore ranges between a minimum and for Burrowing Owls. maximum value over time. We estimated the upper limit of the water table based on local observations at a select number of Methods sites by looking for evidence of a saturation zone We created the Burrowing Owl habitat suitability index using six (i.e.,redoximorphic features in the soil). We defined a water GIS raster layers for inputs, including: soils range site, soil table to be any area that remained saturated for longer than a psamment, depth to water table, slope, vegetation landcover, and month. The soil saturation zone is recorded as three separate hydrology. Habitat suitability values were assigned to each of values in SSURGO, a minimum, maximum, and representative the six GIS raster layers based on NGPC biologists’ value. Given that burrows cannot persist below the water table, recommendations, utilizing a 3-teir classification scheme. we specified suitability for soils with a representative water table Suitable habitat was considered the highest priority and was greater than 121 cm (~4 ft) below the surface. We also assigned a value of 2, where marginally suitable habitat was considered water tables within the upper 60 cm of the soil as assigned a value of 1, and unsuitable habitat was assigned a unsuitable. In areas with a moderate depth to the water table value of 255. The values for each of the six suitability layers (i.e., 61 – 121 cm), Burrowing Owls may create shallower were added together. However, if any pixel within the raster burrows if deeper sites are unavailable. Therefore, these sites layer was classified as unsuitable (i.e., a habitat suitability value were assigned marginal habitat suitability values. of 255), the combined habitat index for that specific area was set to “unsuitable”. Wetlands/Hydrology Wetland and hydrological data are based on the National Soils Wetlands Inventory (NWI) digital wetlands maps of wetland We derived the soil data from the Soil Survey Geographic locations and types as defined by the U.S. Fish and Wildlife Database 2.2 (SSURGO), which is highly considered to be the Service. Data from annual habitat surveys were added to NWI most detailed level of geospatially referenced soil data available for this region by Rainwater Basin Joint Venture (RWBJV). We through the Natural Resources Conservation Service. SSURGO added additional hydrological data to the dataset by using the data layers were created by following national standards. Soils ArcGIS Soil Data Viewer 5.2. Frequently flooded and were digitized using a line segment (i.e., vector) format frequently ponded soils were considered wetlands and were following the NRCS digitizing guidelines. SSURGO data are merged with the NWI layer to give a more detailed map of areas distributed as a complete geographic coverage for a specified prone to soil saturation. All map units covered by this layer soils survey area. Mapping scales generally range from 1:12,000 were assigned as unsuitable. to 1:63,360, which are designed for use by landowners, townships, and county natural resource planning and Vegetation Landcover management. We used the Nebraska Land Cover developed by the Rainwater Basin Joint Venture to prioritize suitable grassland habitat. The

Nebraska Land Cover consists of habitat classes derived from the Hierarchical All Bird System (developed by Playa Lakes Joint Venture), which is employed by RWBJV to estimate current landscape carrying capacity using density based estimates. Habitat classes were selected based on two criteria: 1) the habitat that can be delineated in a GIS format using current GIS datasets, remote sensing techniques, or photo interpretation, 2) the habitat is utilized by priority species and are critical to support priority bird species at goal population levels identified in the national bird conservation plans.

Slopes Fig. 1. Nebraska Black-tailed Prairie Dog and Burrowing Owl suitable habitat Elevation slopes were derived from a 30 meter Digital Elevation greater than 64 acres Model (DEM) downloaded from the U.S. Geological Survey (USGS). Slopes with a 0-10% gradient were assigned as highly Discussion suitable. Slopes of 10-30% gradient were considered marginally The habitat suitability index identified over a quarter of the state suitable and all slopes steeper than a 30% gradient were as potential prairie dog habitat, yet prairie dog colonies occupy considered unsuitable. only a small fraction of that area. This is likely the result of prairie dog eradication, control, and reintroduction activities by Psamment Soils humans. Furthermore, habitat fragmentation remains to be a Psamment is a taxonomic classification that describes certain driving factor influencing prairie dog population decline. Given sandy soils. The soil’s psamment was used to identify Nebraska that there is a total of 14,366,638 acres of suitable habitat Sandhills soils in an attempt to isolate them as an area of identified in the habitat suitability index, only about half of the marginal suitability for Burrowing Owls. We assigned a habitat area had an un-fragmented area greater than or equal to 64 acres. suitability value of 2 to all soils of the taxonomic suborder “Psamment.” These soils were identified using the NRCS Soil The resulting habitat suitability index (Fig. 1) correlates well Series Classification Query. with known prairie dog locations. Panhandle Prairies, Sand-sage Prairie, and Oglala Grassland BULs show some of the greatest Results suitable habitat acres and Kimball Grasslands BUL has a high The model identified 14,366,638 acres in Nebraska as having proportion of suitable area. The Central Loess Hills and the some degree of potentially suitable prairie dog and Burrowing Rainwater Basin BUL are two exceptions, which historically do Owl habitat. High suitability areas were distributed across not have substantial prairie dog densities. However, the area 7,679,501 acres or 15.5% of the state (Fig. 1). Areas containing south of the Central Loess Hills adjacent to the Platte River had the highest suitability for prairie dogs and Burrowing Owls are some of the highest densities of prairie dogs in the east-central typically areas with high arability. As a result, a substantial portion of the state. The Rainwater Basin BUL region is a portion of the suitable areas classified in the model have a high highly fragmented landscape, much of which is driven by degree of habitat fragmentation. The Rocky Mountain Bird agricultural development, and therefore contains little suitable Observatory previously identified 297 prairie dog colonies in habitat for prairie dogs, and subsequently Burrowing Owls. western Nebraska, where the average prairie dog colony was 64 Although the entire region possesses 633,616 acres of suitable acres in size. Smaller colonies are typically classified as habitat, less than half are considered unfragmented areas greater satellites of larger colonies. Therefore, by setting a limit of 64 than 64 acres in size, most of which are part of a USDA research acres as the minimum contiguous area required for a successful facility which does not possess many Black-tailed Prairie Dog prairie dog colony, and subsequently Burrowing Owl habitat, colonies. only 11,634,124 acres would be classified as suitable habitat, while only 4,638,142 acres are classified as highly suitable areas Habitat suitability indices can aid in directing management (Fig. 1). efforts and inform managers where rare or elusive species may likely occur. Additionally, habitat suitability indices may Regionally, the largest estimates of suitable prairie dog and provide insight on how species may respond to particular Burrowing Owl habitat occurred in the Central Loess Hills management actions or habitat conditions. Here we demonstrate Biologically Unique Landscape (BUL; defined by Nebraska that habitat suitability indices may be a useful tool for Game and Parks Commission) with 917,640 acres and 561,509 identifying habitat for both Black-tailed Prairie Dog colonies highly suitable acres. Oglala Grasslands BUL also demonstrates and Burrowing Owls. Once colony locations are identified, high potential for prairie dog and Burrowing Owl habitat. managers can begin to address the habitat and conservation Eighty-four percent of the BUL area provides potentially needs for both the Black-tailed Prairie Dog and the Burrowing suitable habitat and 51% percent of the BUL is estimated to be Owl. highly suitable habitat. When looking at unfragmented habitat greater than 64 acres, those percentages are only slightly reduced For additional information regarding the analysis, results and to 82 and 46% suitable habitat. discussion consult the full document.