PATTERNS OF AVIAN AND BAT MORTALITY AT A UTILITY- SCALED WIND FARM ON THE SOUTHERN HIGH PLAINS by Amanda Miller, B. A THESIS IN WILDLIFE BIOLOGY Submitted to the Graduate Faculty of Texas Tech University in Partial Fulfillment of the Requirements for the Degree of MASTER OF SCIENCE Approved Clint Boal Ph. Committee Chair Ernest Fish Ph. Tigga Kingston Ph.
Laura Nagy Ph. Fred Hartmeister Dean of the Graduate School August 2008 Copyright 2008, Amanda Miller Texas Tech University, Amanda Miller, August 2008 ACKNOWLEDGMENTS There are many individuals whom I would like to acknowledge and thank for their support throughout the course of this study. Foremost, I would like to thank Dr. Clint Boal for bringing me into the project, encouraging my growth as a scientist and providing useful and thoughtful advice throughout this process.
I would like to thank Dr. Tigga Kingston for her support in the bat species portion of the project, Dr. Ernest Fish for his knowledge in geographic information systems and the Panhandle region, and Dr. Laura Nagy for mentoring me through the science-side of the wind energy industry.
I would like to thank Tetra Tech Environmental Consulting Inc.; FPL Energy; the Texas Tech University Graduate School and Department of Natural Resources Management; and the Texas Cooperative Fish and Wildlife Research Unit for funding and support of this opportunity. I would like to thank Dr. Carlos Villalobos for facilitating housing during the field season and Drs. David Wester and Steven Cox for statistical analysis help.
Colton Rose and Mark Davis were invaluable in the field, both on the ground footwork and at night surveying, and I credit them for their hard work. I would like to thank my fellow graduate students for their aid in the field. I would like to thank my husband, Douglas Miller, for encouraging me throughout the 64 weeks of field work and beyond. My family has been a great source of encouragement throughout my education.
ii Texas Tech University, Amanda Miller, August 2008 COMPOSITION OF THESIS This thesis is composed of a literature review of wind energy developments and the consequent avian and bat species interactions and three manuscripts that are formatted for submission to peer-reviewed scientific journals. Chapter I outlines the major findings and limitations of wind energy research in North America. It is composed of a brief introduction to wind energy development and wildlife interactions, a review of previous research related to impacts on avian species, a review of previous research related to impacts on bat species and presentation of the goals of this study. All following chapters are formatted for submission into The Journal of Wildlife Management, a publication of The Wildlife Society.
Chapter II and III explore the patterns of avian and bat mortality, respectively, at a utility-scale wind energy center in the Texas Panhandle. Chapter IV develops a predictive model for bat species mortality based on species’ presence within and geophysical characteristics of a wind energy development along the Caprock Escarpment in Texas. iii Texas Tech University, Amanda Miller, August 2008 TABLE OF CONTENTS Acknowledgments. ii Composition of Thesis.
vii List of Tables. ix List of Figures. 1 Direct Impacts of Wind Energy on Avian Species. 3 Early Studies at California Wind Energy Developments.
3 Recent Studies at North American Wind Energy Developments. 4 Collision mortality at wind energy developments in Canada. 5 Collision mortality at wind energy developments in the Pacific Northwest region. 5 Collision mortality at wind energy developments in the Rocky Mountain region.
6 Collision mortality at wind energy developments in the Midwestern United States. 6 Collision mortality at wind energy developments in the Eastern United States. 7 Patterns of Direct Impacts to Avian Species. 7 Indirect Impacts of Wind energy on Avian Species.
8 Direct Impacts of Wind Energy on Bat Species. 9 Recent Studies at North American Wind Energy Developments. 10 Collision mortality at wind energy developments in Canada. 10 Collision mortality at wind energy developments in the Western United States.
10 Collision mortality at wind energy developments in the Midwestern United States. 11 Collision mortality at wind energy developments in the Eastern United States. 12 Patterns of Direct Impacts to Bat Species. 13 Hypothesis Regarding Bat Species Collision Mortality.
14 Statement of Problem. 16 iv Texas Tech University, Amanda Miller, August 2008 Chapter 2. Avian Mortality at a Utility-scale Wind Energy Development along the Caprock Escarpment. 32 Standardized Carcass Searches.
38 Standardized Carcass Searches. 41 Spatial and Temporal Distribution. 45 Chapter 3: Bat Mortality at a Utility-scale Wind Energy Development along the Caprock Escarpment. 61 Standardized Carcass Searches.
66 Standardized Carcass Searches. 70 v Texas Tech University, Amanda Miller, August 2008 Carcass Persistence. 74 Chapter 4: Geophysical Characteristics that effect Bat Mortality along the Caprock Escarpment. 91 Standardized Carcass Searches.
93 Bat Presence-Absence. 95 Standardized Carcass Searches. 107 vi Texas Tech University, Amanda Miller, August 2008 ABSTRACT Wind energy has been utilized commercially in the United States since the 1970s. Empirical evidence suggests that direct collision mortalities of avian and bat species are consequences of wind energy development.
Texas has the most installed wind energy generation capacity in the United States, yet no empirical data are available to assess the impact to local avian and bat populations. It is the goal of this study to determine the spatial and temporal distribution of avian and bat mortality at a utility-scale wind energy development along the Caprock Escarpment and to develop an accurate mortality estimate for avian and bat mortality at the site. Further, this study seeks to incorporate the year-long continuous mortality study, species use of the site and the site’s geophysical characteristics into a predictive model for wind energy development along the Caprock Escarpment. From September 2006 to September 2007, I conducted standardized carcass searches at 28 turbines and 3 anemometer towers (n = 1,551).
Additionally, I assessed removal rate of carcasses by scavengers and the efficiency of searchers in finding carcasses in trials concurrent to carcass searches. I calculated observer efficiency as the proportion of trial carcasses that were detected by observers, carcass persistence as the average length of time trial carcass remained onsite before complete removal and modeled mortality estimates using the Young et Al. I estimate mortality for bat species for an eight-month season of occupancy, and for avian species on a yearly basis. To identify spatial and temporal distributions, I conducted chi-squared test analysis of deviance for avian and bat taxa separately.
vii Texas Tech University, Amanda Miller, August 2008 During standardized carcass searches, observers detected 25 avian carcasses and 47 bat carcasses. Turkey vultures (Cathartes aura) accounted for 36 percent of avian carcass detections, and Brazilian free-tailed bats (Tadarida brasiliensis) accounted for 94 percent of bat carcass detections. Using a 63 percent observer efficiency rate and a 9.5 day carcass persistence, I estimate avian mortality to be 0.5 individuals per MW per year (SE = 0. I estimate bat mortality to be 36.9 individuals per MW per season of occupancy (SE =111.89) using a 23 percent observer efficiency rate and 1 day carcass persistence.
There was no significant spatial distribution of avian or bat carcasses within the wind energy development. Avian carcass detections were significantly higher during the fall season (χ2 = 20. Bat carcass detections were significantly higher during the fall and spring season (χ2 = 52. The local impact of the Red Canyon Wind Energy Center on avian species appears to be low and similar to results seen in Oklahoma.
In contrast, the relatively high mortality estimate for bat species indicates further study is required. These results are the first publicly available mortality estimates for the Caprock Escarpment region and identify the potential for population-level impacts of collision mortality to local bat species. viii Texas Tech University, Amanda Miller, August 2008 LIST OF TABLES Chapter 1 1. Summary of Direct Impact Studies on Avian Species.
Summary of Direct Impact Studies on Bat Species. Total effort for standardized carcass searches from September 2006 through September 2007. Summary of avian mortality composition based on mortalities detected in standardized search plots from September 2006 through September 2007. Summary of avian species composition based on mortalities detected incidental to standardized carcass searches from September 2006 through September 2007.
Number of avian mortalities detected in standardized search plots per turbine from September 2006 through September 2007, inclusive of all species detected. Results of avian species searcher efficiency trials conducted from September 2006 through September 2007. Results of avian species carcass removal trials conducted September 2006 through September 2007. Total effort for standardized carcass searches from September 2006 through September 2007.
Summary of bat mortality composition based on mortalities detected in standardized search plots from September 2006 through September 2007. Summary of bat species composition based on mortalities detected incidental to standardized carcass searches from September 2006 through September 2007. List of turbines and numbers of bat mortalities detected in standardized search plots from September 2006 through September 2007. Results of bat species searcher efficiency trials conducted from September 2006 through September 2007.
Results of bat species carcass removal trials conducted from September 2006 through September 2007. List of turbines and numbers of bat mortalities detected in standardized search plots from September 2006 through September 2007. List of turbines and numbers of bat mortalities detected in standardized search plots from October to December 2007. 105 ix Texas Tech University, Amanda Miller, August 2008 LIST OF FIGURES Chapter 2 1.
Location of sampled wind turbine generators at Red Canyon Wind Energy Center. Distribution of avian mortalities detected at Red Canyon Wind Energy Center. Distribution of distance from wind turbine generators to avian mortality detections. Temporal distribution of avian mortalities detected at Red Canyon Wind Energy Center.
Location of sampled wind turbine generators at Red Canyon Wind Energy Center. Distribution of distances from turbines to carcasses for bat mortalities detected September 2006 through September 2007. Age composition by species of bat mortalities detected from September 2006 through September 2007. Sex composition by species of bat mortalities detected from September 2006 through September 2007.
Distribution of all bat mortalities detected from September 2006 through September 2007 by month beginning September 2006 through September 2007. Distribution of bat mortalities detected from September 2006 through September 2007 at the Red Canyon Wind Energy Center. Location of sampled wind turbine generators at Red Canyon Wind Energy Center. 106 x Texas Tech University, Amanda Miller, August 2008 CHAPTER 1: INTRODUCTION Wind energy has been commercially used in the United States since the mid-1970s, with increased development beginning in 1992 in response to the Energy Policy Act that offered federal production tax credits in support of renewable energy resource development (United States Government Accountability Office (GAO) 2005).
Individual states provide further incentives for wind energy development through renewable portfolio standards, partnered grants through the U. Department of Energy, and tax incentives. Driven by technological advances that decreased the cost of energy generation from wind resources (Hansen et al. 1992, Redlinger et al.
2002), wind energy has become a major sector of the renewable energy industry (Pasqualetti et al. 2004, United States GAO 2005). Wind energy generation currently occurs in 25 states, and the American Wind Energy Association (AWEA) predicts that 6% of the nation’s energy will be from wind resources by 2020 (AWEA 2005). Wind energy is seen as a “green” energy source, mitigating environmental impacts associated with fossil fuel energy generation (Keith et al.
However, recent studies have indicated that wind energy development is associated with negative impacts on avian and bat species. Negative impacts of wind energy generation can be apportioned into two types: 1) direct mortality due to collision with wind turbine generators, and 2) indirect impacts due to avoidance, habitat disturbance and displacement (National Wind Coordinating Committee 2004). Of the 300-plus wind energy developments currently in operation in North America, only 33 developments have been studied to assess wildlife impacts.