Prairie Dog and Burrowing Owl Habitat Analysis Throughout Nebraska

Home , Burrowing owl, Psamment

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

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

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:

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. Fish and Wildlife Service. Data from annual habitat surveys were added to NWI for this region by the Rainwater Basin Joint Venture (RWBJV). We added additional hydrological data to the dataset by using the ArcGIS Soil Data Viewer 5.2. Frequently flooded and frequently ponded soils were considered wetlands and were merged with the NWI layer to give a more detailed map of areas prone to soil saturation. All map units covered by this layer were assigned a habitat suitability value of 255 (unsuitable). Values were assigned as follows:

Suitability Wetlands 2 Non-wetland 1 Not applicable 255 Wetland

Vegetation Landcover We used the Nebraska Land Cover developed by the Rainwater Basin Joint Venture to prioritize suitable grassland habitat (Table 2). The Nebraska Land Cover consists of habitat classes derived from the Hierarchal All Bird System (developed by Playa Lakes Joint Venture), which is employed by the 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. Additional Land Cover updates are made through photo interpretation and are then integrated into the statewide Nebraska Land Cover. Habitat suitability values were classified as follows:

Suitability Vegetation Landcover 2 51, 71, 73, 75, 77, 247 1 87 255 1, 12, 13, 14, 15, 31, 32, 33, 34, 35, 36, 38, 39, 41, 42, 44, 46, 48, 59, 60, 61, 63, 66, 69, 101, 102, 103, 104, 106, 121, 122, 141, 142, 143, 152, 153, 201, 202, 203, 206, 207, 208, 209, 211, 241, 242, 243, 244, 245, 246, 248

Table 2. HABS Habitat Associations, Conditions, and Codes for Nebraska Landcover “DIVISION” “TYPE” ASSOCIATION CONDITION 1 – Reservoirs/ 101 - Sandhill Lake Aquatic Open Water Lakes/Ponds 102 - Lagoon

“DIVISION” “TYPE” ASSOCIATION CONDITION 103 - Pit 104 - Reservoir 106 - Stock pond 121 - Farmed* 12 - Playas 122 - Grassland/Buffered* 13 - Sandhill Wetlands 141 - RWB farmed Wetlands 14 - Rainwater Basins 142 - RWB early successional 143 - RWB late successional 152 - Emergent marsh 15 - Other Wetlands 153 - Saline 241 - Riparian canopy 242 - Exotic riparian shrubland 243 - Native riparian shrubland 244 - River channel Riverine Systems 24 - Riverine Systems 245 - Unvegetated sandbar 246 – Warm-water slough 247 - Wet meadow 248 - Floodplain marsh 201 - Alfalfa 202 - Corn 203 - Fallow 206 - Sorghum 38 - Cropland 207 - Soybeans 208 - Sunflowers 209 - Wheat Anthropogenic Agricultural 211 - Other 31 - Grasses 32 - Trees - upland 33 - Trees - riparian 39 - CRP 34 - Wetland 35 - Playa/non-floodplain wetland 36 - CRP other practices 48 - All other types 46 - Urban/Suburban Other Other 40 - Other 44 – 4 lane roads 42 - Rural developed 41 - Other roads Sparsely Vegetated 51 - Badlands 61 - Forest/ Woodland 61 - Forest/Woodland (Upland) (upland) 59 - Eastern red cedar Terrestrial Forests/Woodlands 66 - Juniper 69 - Few trees, grassy understory 63 - Ponderosa Pine 60 – Many trees, little grassy understory 71 - Mixedgrass Terrestrial Grasslands 73 - Sandhills Grasslands 75 - Shortgrass

“DIVISION” “TYPE” ASSOCIATION CONDITION 77 - Tallgrass 87 - Sand Sage

*Loess Hills (Table Playas) and Loess Canyon classes only.

Slopes Elevation slopes were derived from a 30 meter Digital Elevation Model (DEM) downloaded from the U.S. Geological Survey (USGS). Habitat suitability values were assigned according to the original black-tailed prairie dog model using the following suitability classifications:

Suitability Slope 2 0 - 10% 1 10 – 30% 255 > 30%

Psamment Soils Psamment is a taxonomic classification that describes certain sandy soils. The soil’s psamment was used to identify Nebraska Sandhills soils in an attempt to isolate them as an area of marginal suitability for burrowing owls. We assigned a habitat suitability value of 255 to all soils of the taxonomic suborder “Psamment.” These soils were identified using the NRCS Soil Series Classification Query. Nineteen soil series were identified, including: Blueridge, Boone, Colfer, Dankworth, Duda, Dwyer, Els, Fishberry, Ipage, McKelvie, Natick, Niobrara, Norway, Pahuck, Orpha, Sarpy, Scoville, Simeon, Valent, Valentine. Values were assigned as follows:

Suitability Psamment Soil Classification 2 Non-psamment soils 255 Psamment and non-soil areas (i.e., water)

Results

The model identified 14,366,638 acres in Nebraska as having some degree of potentially suitable prairie dog and burrowing owl habitat, which is equivalent to 29% of the state (figure 1). High suitability areas account for 7,679,501 acres or 15.5% of the state. Areas containing the highest suitability for prairie dogs and burrowing owls are typically areas with high arability. As a result, a substantial portion of the suitable areas classified in the model have a high degree of habitat fragmentation. The Rocky Mountain Bird Observatory (RMBO) previously identified 297 prairie dog colonies in western Nebraska, where the average prairie dog colony was 64 acres in size. Smaller colonies are typically classified as satellites of larger colonies. Therefore, by setting a limit of 64 acres as the minimum contiguous area required for a successful prairie dog colony, and subsequently burrowing owl habitat, only 11,634,124 acres or 23% of the state

7 would be classified as suitable habitat, while only 4,638,142 acres is classified as highly suitable areas or 9.4% of the state (Table 4, figure 2).

Regionally, the greatest estimated areas of suitable prairie dog and burrowing owl habitat occurs in the Central Loess Hills BUL with 917,640 acres and 561,509 highly suitable acres (Table 3), 860,605 acres and 406,060 acres, respectively, of contiguous areas greater than 64 acres (Table 4). Oglala Grasslands BUL also demonstrates high potential for prairie dog and burrowing owl habitat. Eighty-four percent of the BUL area provides potentially suitable habitat and 51% percent of the BUL is estimated to be highly suitable habitat. When looking at unfragmented habitat greater than 64 acres, those percentages are only slightly reduced to 82 and 46% suitable habitat.

Figure 1. Nebraska black-tailed prairie dog and burrowing owl habitat suitability index

Figure 2. Nebraska black-tailed prairie dog and burrowing owl suitable habitat greater than 64 acres

Table 3. Prairie dog suitability estimates classified by the biologically unique landscape for Nebraska. High % High BUL Name BUL Acres Suitable Acres % Suitable Suitabilty Suitability Central Loess Hills BUL 1,402,596 917,640 65.4 561,509 40.0 Panhandle Prairies BUL 1,178,079 877,987 74.5 134,532 11.4 Sandsage Prairie BUL 1,034,642 677,084 65.4 114,929 11.1 Rainwater Basin BUL 3,930,800 633,616 16.1 581,560 14.8 Oglala Grasslands BUL 715,494 601,796 84.1 368,182 51.5 Verdigris-Bazile BUL 701,656 329,082 46.9 135,759 19.3 Wildcat Hills BUL 418,528 315,920 75.5 78,614 18.8 Pine Ridge BUL 526,704 224,931 42.7 83,250 15.8 Loess Canyons BUL 337,958 221,166 65.4 111,238 32.9 Kimball Grasslands BUL 270,089 197,276 73.0 72,840 27.0 Keya Paha BUL 362,251 127,373 35.2 36,457 10.1 Sandstone Prairies BUL 264,917 110,174 41.6 95,510 36.1 Southeast Prairies BUL 579,081 96,685 16.7 66,347 11.5 Middle Niobrara BUL 339,936 49,609 14.6 11,473 3.4 Elkhorn Confluence BUL 94,204 27,749 29.5 113 0.1 Ponca Bluffs BUL 103,096 26,551 25.8 13,337 12.9 Platte Confluence BUL 198,882 18,597 9.4 4,274 2.1 Cherry County Wetlands BUL 1,752,475 13,745 0.8 58 0.0 Dismal River Headwaters BUL 663,348 10,591 1.6 12,334 1.9 Elkhorn River Headwaters BUL 1,279,669 7,691 0.6 0 0.0 Willow Creek Prairies BUL 56,919 7,477 13.1 427 0.7 Sandhills Alkaline Lakes BUL 883,532 2,901 0.3 4 0.0 Thurston-Dakota Bluffs BUL 27,741 2,353 8.5 1,140 4.1 Indian Cave Bluffs BUL 16,646 2,256 13.6 1,230 7.4 Rulo Bluffs BUL 3,024 497 16.4 285 9.4

Table 4. Prairie dog suitability estimates > 64 acres classified by biologically unique landscapes for Nebraska. High % High BUL Name BUL Acres Suitable Acres % Suitable Suitabilty Suitability Central Loess Hills BUL 1,402,596 860,605 61.4 406,060 29.0 Panhandle Prairies BUL 1,178,079 859,155 72.9 116,147 9.9 Sandsage Prairie BUL 1,034,642 645,778 62.4 76,659 7.4 Oglala Grasslands BUL 715,494 589,793 82.4 333,354 46.6 Wildcat Hills BUL 418,528 307,624 73.5 56,036 13.4 Rainwater Basin BUL 3,930,800 294,209 7.5 226,788 5.8 Verdigris-Bazile BUL 701,656 278,210 39.7 57,709 8.2 Loess Canyons BUL 337,958 206,499 61.1 57,125 16.9 Pine Ridge BUL 526,704 199,209 37.8 61,338 11.6 Kimball Grasslands BUL 270,089 192,464 71.3 56,176 20.8 Keya Paha BUL 362,251 101,962 28.1 20,967 5.8 Sandstone Prairies BUL 264,917 79,972 30.2 58,735 22.2 Middle Niobrara BUL 339,936 33,885 10.0 3,330 1.0 Southeast Prairies BUL 579,081 33,297 5.7 10,624 1.8 Ponca Bluffs BUL 103,096 17,448 16.9 1,958 1.9 Elkhorn Confluence BUL 94,204 15,408 16.4 4,094 4.3 Platte Confluence BUL 198,882 13,059 6.6 812 0.4 Cherry County Wetlands BUL 1,752,475 6,909 0.4 0 0.0 Dismal River Headwaters BUL 663,348 4,066 0.6 0 0.0 Elkhorn River Headwaters BUL 1,279,669 3,993 0.3 0 0.0 Willow Creek Prairies BUL 56,919 3,450 6.1 0 0.0 Sandhills Alkaline Lakes BUL 883,532 1,135 0.1 0 0.0 Thurston-Dakota Bluffs BUL 27,741 644 2.3 0 0.0 Indian Cave Bluffs BUL 16,646 406 2.4 0 0.0 Rulo Bluffs BUL 3,024 0 0.0 0 0.0

Discussion

The habitat suitability index identified over a quarter of the state as potential prairie dog habitat, yet prairie dog colonies occupy only a small fraction of that area. This is likely the result of prairie dog eradication, control, and reintroduction activities by humans. In addition, habitat fragmentation is another driving factor of prairie dog range reduction. Given that there is a total of 14,366,638 acres of suitable habitat identified in the habitat suitability index, only about half of the area had an un-fragmented area greater-than or equal-to 64 acres.

The habitat suitability index corresponds fairly well with known prairie dog locations (Figure 3). Panhandle Prairies, Sand-sage Prairie, and Oglala Grassland BULs show some of the greatest suitable habitat acres and Kimball Grasslands BUL has a high proportion of suitable area. The major exceptions are the Central Loess Hills BUL, which historically has not had substantial prairie dog densities, and the Rainwater Basin BUL. However, historically the area to the south of the Central Loess Hills adjacent to the Platte river had some of the highest densities of prairie dogs in the east-central portion of the state. The Rainwater Basin BUL region is a highly fragmented landscape, much of which is driven by agricultural development, and therefore contains little suitable habitat for prairie dogs and subsequently burrowing owls. While the entire region possesses 633,616 acres of suitable habitat, less than half, 294,209 acres are considered un-fragmented areas greater than 64 acres in size, most of which are part of a USDA research facility which does not possess any black-tailed prairie dog colonies. However, the model likely performs well in eastern Nebraska and the Sandhills where land-use and soil characteristics limit prairie dog habitat potential.

Habitat suitability indices can aid in directing management efforts and inform managers where species may likely occur. Additionally, habitat suitability indices may provide light on how species may respond to particular management actions or habitat conditions. Here we show that habitat suitability indices may be a useful tool to identify suitable habitat for both black-tailed prairie dog colonies as well as burrowing owls. Managers can use the black-tailed prairie dog habitat suitability index to search areas where colonies may likely occur. Once colony locations are identified, managers can begin to address the habitat and conservation needs of both the black-tailed prairie dog and the burrowing owl.

Figure 3. Nebraska’s biologically unique landscapes and historic black-tailed prairie dog colony locations.

Literature Cited Butts, K. O. and J. C. Lewis. 1982. The importance of prairie dog towns to burrowing owls in Oklahoma. Proceedings of the Oklahoma Academy of Science 62:46-52.

Conway, C. J., V. Garcia, M. D. Smith, L. A. Ellis, and J. L. Whitney. 2006. Comparative demography of Burrowing Owls in agricultural and urban landscapes in southeastern Washington. Journal of Field Ornithology 77:280-290.

Schneider, R., M. Humpert, K. Stoner, G. Steinauer. 2005. The Nebraska Natural Legacy Project: A Comprehensive Wildlife Conservation Strategy. Nebraska Game and Parks Commission, Lincoln, NE.