Factors Influencing Snowshoe Hare (Lepus Americanus) in Michigan
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Factors influencing snowshoe hare (Lepus americanus) in Michigan By David Michael Burt A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of Fisheries and Wildlife – Master of Science 2014 ABSTRACT Factors influencing snowshoe hare (Lepus americanus) in Michigan By David Michael Burt The goal of my thesis was to identify the climatic and vegetation factors that influence snowshoe hare occupancy in Michigan. My objectives were to: 1) quantify snowshoe hare occupancy as related to climate change and 2) quantify the relationships between patch-level snowshoe hare occupancy and land cover change over time, current land cover, habitat structure, and mesocarnivore presence. In Chapter 1, I determined the most efficient transect configurations for winter track surveys and found that transects 150m in length with 100 or 75m spacing, or 125m in length with 75m spacing provided reliable estimates of hare occupancy. In Chapter 2, I researched climatic variables that are potentially linked to snowshoe hare population performance and assessed whether those factors affected the localized extinction of snowshoe hares. I found that localized extinction was influenced by maximum temperature from May 15 – January 19; as temperature increased the likelihood of localized extinction increased. I also found that the total number of days with measurable snow on the ground affected localized extinction; as number of days with snow on the ground decreased the likelihood of localized extinction increased. In Chapter 3, I evaluated whether land cover change over time, current land cover, and habitat factors affected snowshoe hare occupancy and habitat use. I found that land cover change over time did not affect hare occupancy. Rather, a current land cover covariate (the ratio between forest and open edge) and the habitat covariates of visual obstruction at 1.0-1.5m above snow level and stem density were important; all 3 parameters were positive but only the transect-level covariates were significant. ACKNOWLEDGEMENTS Funding for this project was provided by the Michigan Department of Natural Resources – Wildlife Division through the Michigan Federal Aid in Wildlife Restoration program grant F13AF01268 in cooperation with the U.S. Fish and Wildlife Service, Wildlife and Sport Fish Restoration Program, and Safari Club International Michigan Involvement Committee. I greatly appreciate the mentoring provided by my advisor, Gary Roloff, who always made time to provide guidance, helped me advance in my career path, and was always supportive of what I was trying to accomplish. Thank you to my committee members Rique Campa, III, Barbara Lundrigan, and Dwayne Etter for their support and involvement with this project. I am grateful for the help, effort, advice and encouragement of all my previous and current lab mates, lab employees, and field crews. Without their generous support, I would have had trouble accomplishing the goals I set out to achieve. I would like to especially thank Steven Gray, Alex Killion, Daniel Linden, Robert Montgomery, Paul Nelson, Clint Otto, andTracy Swem. I appreciate the numerous interviewees who graciously made themselves and their knowledge available for identifying historic hare sites. I would like to thank Michigan Department of Natural Resources - Wildlife Division employees J. Belman, D. Beyer, D. Brown, J. Lukowski, K. Sitar, K. Swanson, T. Swearingen, and C. VanHorn for their assistance with fence construction and/or data collection at the Cusino Wildlife Research Area. In addition, thanks to R. Aikens and B. Sillet of the Sault Ste. Marie Tribe of Chippewa for their help in fence construction at Cusino, the replication of the research at Kinross, and their commitment as a partner to this research project. I am also thankful for iii the assistance of MDNR - Wildlife Division employees D. Brown, T. Lyon, T. Maples, V. Richardson, B. Rollo, J. Valentine, and M. Wegan for helping with field data collection. Also, thanks to S. Beyer from MDNR for helping manage the social and political aspects of the project. Thanks to T. Minzey for coordinating my attendance at sportsperson coalition meetings and M. Donovan for help brainstorming analysis methodologies and ways to map land cover. Last, but not least, thank you to my family and friends who supported and encouraged me throughout this state of my life. In particular Ashley Burt, Kristen Burt, Michael Burt, Kathleen Morris, Daniel O’Connor, Mitzi Palms-Burt, Lisa Rumsey, and Karalyn Yermak. iv TABLE OF CONTENTS LIST OF TABLES vii LIST OF FIGURES ix INTRODUCTION 1 LITERATURE CITED 6 CHAPTER 1 RELIABILITY OF WINTER TRACK COUNTS FOR QUANTIFYING SNOWSHOE HARE OCCUPANCY 9 ABSTRACT 9 1.1. INTRODUCTION 10 1.2. STUDY AREA 12 1.3. METHODS 13 1.3.1. Data Analysis 14 1.4. RESULTS 16 1.5. DISCUSSION 17 1.6. ACKNOWLEDGEMENTS 20 APPENDIX 21 LITERATURE CITED 28 CHAPTER 2 CLIMATIC FACTORS INFLUENCING THE DISTRIBUTION OF SNOWSHOE HARES 32 ABSTRACT 32 2.1. INTRODUCTION 33 2.2. STUDY AREA 36 2.3. METHODS 37 2.3.1. Site Selection 37 2.3.2. Field Sampling 38 2.3.3. Climate Covariates 39 2.3.4. Data Analysis 40 2.4. RESULTS 40 2.5. DISCUSSION 42 2.6. ACKNOWLEDGEMENTS 45 APPENDIX 47 LITERATURE CITED 54 v CHAPTER 3 LAND COVER AND VEGETATION FACTORS INFLUENCING SNOWSHOE HARE OCCUPANCY IN MICHIGAN 60 ABSTRACT 60 3.1. INTRODUCTION 61 3.2. STUDY AREA 64 3.3. METHODS 65 3.3.1 Site Selection 65 3.3.2 Field Sampling 66 3.3.3 Data Analysis 69 3.4. RESULTS 70 3.4.1 Land Cover Change Over Time 71 3.4.2 Current Land Cover and Habitat Structure 72 3.5. DISCUSSION 73 3.6. MANAGEMENT IMPLICATIONS 76 3.7. ACKNOWLEDGEMENTS 78 APPENDIX 79 LITERATURE CITED 91 CONCLUSIONS 96 LITERATURE CITED 99 vi LIST OF TABLES Table 1.1. Snowshoe hare densities, track survey efforts, location of surveys, and year(s) that surveys were completed in ~6.1ha enclosures, Upper Peninsula of Michigan, USA. 22 Table 1.2. Transect dimensions, the number of transects in a ~6.1ha study site, and distance traversed during snow track surveys for snowshoe hares. Table includes the 10 combinations of transect length and spacing that produced ≥90% accuracy for estimating site occupancy. The efficiency is determined by the total distance walked for a complete survey. 23 Table 2.1. Climate covariates identified from the literature review, associated citation, and observed relationship to snowshoe hare population demographics. 48 Table 2.2. Candidate model set for estimating the likelihood of a localized snowshoe hare population going extinct in Michigan. LL = log-likelihood, ∆AIC = difference in AIC value from top-ranking model, k = model parameters, ωi – Akaike weight of evidence. 49 Table 2.3. Means (SE) and ranges of climate covariates used for estimating the likelihood of a localized snowshoe hare population going extinct in Michigan. 50 Table 3.1. Sample level, means (SE), and ranges of land cover and habitat covariates used for estimating localized snowshoe hare occupancy (site level only) or habitat use (transect level) in Michigan. 80 Table 3.2. Candidate model set for estimating the likelihood of a localized site being occupied by snowshoe hare in Michigan. ∆AIC = difference in AIC value from top-ranking model, k = model parameters, ωi – Akaike weight of evidence. 81 Table 3.3. Top 6 ranking models with variables from site and transect levels from the 41 candidate models (Table 3.5) for estimating the likelihood of a site being currently occupied by snowshoe hare in Michigan. ∆AIC = difference in AIC value from top-ranking model, k = model parameters, ωi – Akaike weight of evidence. 82 Table 3.4. The relationship between visual obstruction and stem densities in 3 forest types. Compiled from stem densities and visual obstruction measured at 117 sites in the northern Lower and Upper Peninsulas of Michigan, winter of 2013. 83 vii Table 3.5. List of all 41 candidate models used in current occupancy modeling for estimating the likelihood of a site being currently occupied by snowshoe hare in Michigan. 84 viii LIST OF FIGURES Figure 1.1. The geographic range of snowshoe hares (diagonal striping), with Michigan outlined in bold black (map inset), and the locations of Cusino and Kinross hare enclosures, Upper Peninsula of Michigan, winters of 2012-2014. The geographic range of hares was adapted from the International Union for Conservation of Nature (www.iucnredlist.org/technical-documents/spatial-data#mammals). 24 Figure 1.2. Schematic of how snowshoe hare tracks in enclosures were subsampled including (A) the outline of the enclosures (black) with 9 transects spaced 25m apart (gray), (B) snowshoe hare tracks during 1 survey as black circles, (C) random locations generated on each transect to denote the start of transect segments for 1 iteration as black 4-pointed stars, (D) transect segments of 25m on each transect as black lines originating from the black 4-pointed stars, (E) snowshoe hare tracks that intercepted transect segments, and (F) example of the results of 1 iteration with 100m spacing. 25 Figure 1.3. Proportion of 10,000 iterations that a site was correctly deemed as occupied for all transect configurations at hare densities of (A) 1.5, (B) 1.2, (C) 0.8, (D) 0.5, and (E) 0.2 hares/ha. The 90% accuracy threshold is designated by the black horizontal line. 26 Figure 1.4. The average number of transects occupied at each of the 5 hare densities for the 3 most efficient transect configurations: 125 m length x 75 m spacing, 150 m length x 75 m spacing, and 150 m length x 100 m spacing. 27 Figure 2.1. Location and occupancy status of snowshoe hare survey sites throughout the northern Lower and Upper Peninsulas of Michigan, USA, winter 2013.