Mapping of Black-tailed Prairie Dog (Cynomys ludovicianus) Colonies using National Agriculture Imagery Program (NAIP) 2015 Imagery Prepared for: Bureau of Land Management, Miles City Field Office By: Daniel A. Bachen, Bryce A. Maxell, Alexis L. McEwan, Boaz Crees Montana Natural Heritage Program Natural Resource Information System Montana State Library March 2017 Mapping of Black-tailed Prairie Dog (Cynomys ludovicianus) Colonies using National Agriculture Imagery Program (NAIP) 2015 Imagery Prepared for: Bureau of Land Management, Miles City Field Office Agreement Number: L11AP20008 Prepared by: Daniel A. Bachen, Bryce A. Maxell, Alexis L. McEwan, Boaz Crees © 2017 Montana Natural Heritage Program P.O. Box 201800 • 1515 East Sixth Avenue • Helena, MT 59620-1800 • 406-444-3290 i This document should be cited as follows: Bachen, D.A., B.A. Maxell, A.L. McEwan, and B. Crees. 2016. Mapping of Black-tailed Prairie Dog (Cynomys ludovicianus) colonies using National Agriculture Imagery Program (NAIP) 2015 Imagery. Montana Natural Heritage Program, Helena, Montana. 18 p. ii EXECUTIVE SUMMARY Black-tailed Prairie Dogs (Cynomys ludovicianus) there was evidence of current or recent alter vegetation and dig extensive burrows, occupancy by Black-tailed Prairie Dogs. Our creating habitat for other species, and serve as ground truthing efforts were based on 1 ha grid prey for both mammalian and avian predators. cells overlaid on each colony. We walked the Several animal species of conservation concern perimeter of Category 1 complexes and at the state and federal level, including the recorded whether grid cells of the colony were Mountain Plover (Charadrius montanus), active, inactive, or no evidence of occupancy. Of Burrowing Owl (Athene cunicularia), and Black- the 56 colonies we ground truthed, 95% had footed Ferret (Mustela nigripes), are closely evidence of current or recent occupancy. At the associated with prairie dog colonies and make grid cell level, we found that cells along mapped use of burrows or the prairie dogs themselves. boundaries contained evidence of Black-tailed Recently, prairie dog populations have been Prairie Dogs only 37% of the time while 76% of impacted by sylvatic plague causing colony and cells within the boundaries had evidence. population dynamics to change. The Montana Our methods appear to have been effective at Conservation Plan for Black-tailed and White- identifying colonies, but less precise at tailed Prairie Dogs identifies the need to determining the exact boundaries of these monitor the distribution of these animals within colonies. Some inaccuracies may have resulted the state to aid in the conservation of prairie from the time delay between collection of the dogs and dependent species. NAIP imagery and collection of ground truthing We addressed the need for colony and complex data. With future improvements in image monitoring by digitizing potential colony quality and resolution our precision and boundaries across Southcentral and Southeast accuracy will increase, thereby negating or Montana using 2015 National Agriculture minimizing the need to ground truth digitized Imagery Program (NAIP) imagery. In total, we colonies for future projects. mapped 4,154 potential colonies covering This project documented relatively large areas 556,136 acres. Of these colonies, 4 were over occupied by Black-tailed Prairie Dogs, including 5,000 acres in size, 55 were between 1,000 and several complexes that may be suitable for 5,000 acres, and the remaining 3,199 were less targeted conservation efforts for species such than 1,000 acres. We aggregated colonies into as Black-footed Ferrets. With the development complexes using the 1.5 km rule, and found that of an oral plague vaccine, identification and 15 complexes contained at least 5,000 acres of monitoring of colonies and complexes will be colonies and met the Category 1 criteria under increasingly important. Mapping colonies from the Montana Conservation Plan for Black-tailed NAIP imagery may provide a cost effective way and White-tailed Prairie Dogs. to prioritize areas for vaccine deployment and To test the accuracy of our mapping, we ground monitor the effects on colony size. truthed a subset of our colonies to determine if iii ACKNOWLEDGEMENTS We extend considerable thanks and appreciation to all who conducted surveys for this project including: Boaz Crees, Alexis McEwan, and Ellen Whittle. Thanks to Braden Burkholder for assistance with the Prairie Dog database, Scott Blum for formatting the data and appending it to the Montana Natural Heritage Program’s central animal observation database, and Bryce Maxell for providing valuable feedback throughout the project. We thank the Miles City Field Office of the Bureau of Land Management for providing funding and guidance for this project. This project was supported by an agreement between the Bureau of Land Management and the Montana Natural Heritage Program, a cooperative program of the Montana State Library and the University of Montana (BLM L11AP20008) iv TABLE OF CONTENTS Introduction .................................................................................................................................................. 1 Project Goals ................................................................................................................................................. 2 Methods ........................................................................................................................................................ 3 Digitization of Colony Boundaries ........................................................................................................ 3 Ground Truthing of Select Colonies ...................................................................................................... 3 Data Preservation and Dissemination ................................................................................................. 4 Results ........................................................................................................................................................... 5 Mapping ................................................................................................................................................ 5 Ground Truthing ................................................................................................................................... 5 Discussion...................................................................................................................................................... 6 Literature Cited ............................................................................................................................................. 9 List of Figures Figure 1. Example of a mapped colony boundary ........................................................................... 10 Figure 2. Overview of mapped colonies using 2015 NAIP imagery ................................................. 11 Figure 3. Comparison across projects of mapped colony size ......................................................... 12 Figure 4. Map showing all 1.5 km complexes ................................................................................. 13 Figure 5. Complexes that meet Category 1 criteria ......................................................................... 14 Figure 6. Ground truthed colonies showing proportion with evidence of Black-tailed Prairie Dogs .......................................................................................................................................... 15 Figure 7. Proportion of interior and exterior grid cells with active, inactive and no evidence of Black-tailed Prairie Dogs .................................................................................................. 16 Figure 8. New colony detections ..................................................................................................... 17 Figure 9. Proportion of cells surveyed compared to proportion with activity ................................ 18 v INTRODUCTION Black-tailed Prairie Dogs (Cynomys ludovicianus) Black-tailed Prairie Dogs. The 2005 and 2009 alter vegetation and dig extensive burrows, NAIP projects were 69% accurate at identifying creating habitat for associated species, and colonies and 80% accurate at identifying cells serve as prey for both mammalian and avian within these colonies in areas of the state predators. Although this species is still where colonies are easily distinguished from the widespread throughout much of its historic background vegetation, geological, and range in Montana, sylvatic plague and biological features (Maxell et al. 2010). anthropogenic factors have reduced average However, the 2005 NAIP imagery delineated colony size and changed colony dynamics colonies in Custer, Phillips, and Rosebud (Augustine et al. 2008a), with concomitant counties, had ground truthed accuracies of 51%, impacts on dependent species such as 52%, and 35% respectively for the proportion of Mountain Plover (Charadrius montanus), cells within a colony that had evidence of Black- Burrowing Owl (Athene cunicularia), and the tailed Prairie Dogs. The low accuracies in these federally Endangered Black-footed Ferret counties may be caused by barren areas that (Mustela nigripes) (Augustine et al. 2008b, can superficially resemble the structure of Desmond et al. 2000, Matchett et al. 2010). To prairie dog colonies. Accuracy of mapping at the address the conservation needs of prairie dogs colony level was also relatively inaccurate for within the state, the Montana Prairie Dog these same counties, with only 50%, 46%, and Working Group released a conservation plan in 32% of digitized colonies containing evidence of 2002 to identify objectives for conservation occupancy. These inaccuracies are problematic planning, including quantifying distribution and as these counties overlap core areas for this abundance (MPDWG 2002). species within the state. Therefore, better information about colony coverage in these Since the 1980’s several projects have sought to areas is necessary as conservation and quantify the area occupied by both Black-tailed management of Black-tailed Prairie Dog Prairie Dogs and White-tailed Prairie Dogs colonies is essential for the conservation of a (Cynomys leucurus) within the state (MPDWG number of Montana Species of Concern, and 2002). Over the last decade, the Montana directly effects reintroduction efforts for the Natural Heritage Program (MTNHP) has mapped Endangered Black-footed Ferret. colonies using the 2005 and 2009 National Agriculture Imagery Program (NAIP) imagery Montana’s Conservation Plan for Black-tailed (Maxell et al. 2010). Mapping from aerial and White-tailed Prairie Dogs (MPDWG 2002) imagery can be a relatively cost efficient way to identifies two objectives that can be address identify colonies, particularly on inaccessible with mapping colonies from aerial imagery. public and private lands. However, two major Objective #2 is to “develop statewide and shortcomings exist when these methods are regional prairie dog distribution and abundance used. First, colony boundaries are mapped on standards”. To satisfy these objectives the plan the presence of burrows; therefore, it is not calls for inventory and monitoring of possible to distinguish between active and distribution and abundance and identification inactive colonies or active and inactive areas of complexes of colonies. While abundance within colonies. Second, features similar to within colonies cannot be addressed with aerial burrows may confound colony boundaries or mapping, this technique is well suited to cause colonies to be mapped in areas without quantifying distribution. Objective 3C: “identify 1 isolated prairie dog colonies in need of special improved resolution of the 2015 NAIP imagery consideration, assess their needs, and relative to earlier NAIP imagery impacted the implement special management tasks, as accuracy of identifying colonies in previously appropriate” can be addressed. problematic areas, we intensively ground truthed colonies on accessible public lands in The plan also identifies specific goals for the central Custer County as well as confirming the conservation of Black-tailed and White-tailed presence of Black-tailed Prairie Dogs at other Prairie Dogs and associated species. Specifically, colonies across the rest of the mapped area. three categories are used to describe colony complexes (MPDWG 2002; pages 15-16): Category 1: A minimum of two Black-tailed PROJECT GOALS Prairie Dog complexes sufficient to maintain viable populations of Black-footed Ferrets. Our primary goals for these efforts were to: These should be at least 100 km apart, with  Use NAIP imagery to map areas with recent each encompassing at least 5,000 acres of evidence of Black-tailed Prairie Dog activity Black-tailed Prairie Dogs  Evaluate accuracy of this methodology Category 2: A total of 36,000 acres occupied through ground truthing of 1-hectare grid by Black-tailed Prairie Dogs, composed of at cells least 20 complexes of at least 1,000 acres  Identify complexes for management and potential Black-footed Ferret reintroduction Category 3: Complexes less than 1,000 acres using a 1.5 km separation rule for defining a in size… plus scattered isolated colonies of complex any acreage  Confirm the presence of Black-tailed Prairie To address these needs we mapped colonies of Dogs at colonies outside of the boundaries Black-tailed Prairie Dogs using the 2015 NAIP of historic colonies imagery across some or all of Golden Valley,  Provide data products to partners for Stillwater, Musselshell, Bighorn, Yellowstone, management actions, planning, ground Treasure, Rosebud, Prairie, Powder River, truthing, and environmental reviews Carter, and Custer counties. To determine if the 2 METHODS Digitization of Colony Boundaries We prioritized ground truthing of colonies with high value for conservation of associated Colony boundaries were delineated on the 2015 species, in particular Black-footed Ferrets. To NAIP 20 kilometer × 20 kilometer tiles following sustain a ferret population, large aggregations methods used for the previous projects (see of prairie dog colonies are required (Biggins et Maxell et al. 2010). However, we chose to al. 1993). To ensure that our ground truthing delineate colony boundaries precisely instead of results were most accurate within high priority classifying 1-hectare grid cells as occupied. As areas we allocated the most effort to colonies the area of coverage was relatively small, and to within the largest identified complexes. reduce observer bias, a single technician conducted all of the mapping. All digitization To create colony complexes (hereafter was conducted using Arc Map 10.4 © ESRI complexes), we buffered all colonies by 750 m. Software. We examined the 2015 NAIP imagery We then grouped colonies by overlap between at a scale of approximately 1:3,000 for features these buffers to identify complexes of colonies found within colonies such as mounding of dirt within 1.5 km of each other. Finally, we outside of burrow entrances, and clipped calculated the total size in acres of mapped vegetation. When a potential colony was colonies within each complex. We focused our identified, we digitized the boundary as a ground truthing efforts on complexes meeting polygon feature in a File Geodatabase (Figure the Category 1 criteria (i.e. > 5,000 acres of 1). The colony boundary was then reviewed active colonies). To facilitate surveys, we with previously mapped colonies and point overlaid a public lands layer on all colonies observations overlaid, and any additional areas within the Category 1 complexes and prioritized of occupancy detected on the 2015 NAIP publically accessible areas for survey. imagery were mapped. Polygons were coded as Depending on the priority of each colony we having been detected blind, with the aid of used one of two methods. For high priority previously mapped colonies, or reported colonies in Category 1 complexes, we overlaid a observations. 1-hectare × 1-hectare grid and identified cells in Ground Truthing of Select Colonies proximity to the mapped boundary. Field personal used GPS units with hectare centroids To determine the accuracy of colony boundaries pre-loaded and hard copy maps with the delineated using the 2015 NAIP imagery, we hectare boundaries to identify each grid cell ground truthed a subset of mapped colonies. All within and adjacent to colonies. They then fieldwork was conducted over 30 person/days walked the colony boundary and scored in September 2016. Our goals for this effort whether each hectare grid cell contained active were to quantify the accuracy of mapped burrows, inactive burrows, or no evidence of colonies on two levels: occupancy. For colonies that were either within  Colony: Did the mapped colony contain these Category 1 complexes and visible, but not evidence of Black-tailed Prairie Dogs? accessible or outside of complexes, we sought  Within colony: What was the only to determine if there was evidence of proportion of area with evidence of prairie dog activity at the colony level. prairie dog activity? Personnel traveled as close as possible to these colonies and looked for evidence of Black-tailed 3 Prairie Dogs or their burrows. As any inference Prairie Dog and Point Observation databases. of absence using this survey method would be Spatial data containing both the mapped colony untrustworthy due to incomplete survey boundaries and ground truthing was appended coverage, we only recorded if the colony was to Montana’s statewide Prairie Dog Database active or inactive. and information from this database is available upon request. The observations of active Black- Data Preservation and Dissemination tailed Prairie Dogs and other incidental species To archive and make project data available to observed during surveys were appended to the land managers for use in conservation efforts MTNHP’s point observation database, and are and land use planning, we added the mapped available upon request and through online tools colony boundaries and observation information in the Natural Heritage Map Viewer web to the Montana Natural Heritage Program’s application. 4