Tanglehead) for Grassland Birds
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INVASION BY A NATIVE GRASS: IMPLICATIONS OF INCREASED DOMINANCE OF HETEROPOGON CONTORTUS (TANGLEHEAD) FOR GRASSLAND BIRDS A Thesis by BRIAN JOHN BIELFELT Submitted to the College of Graduate Studies Texas A&M University-Kingsville in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE May 2013 Major Subject: Rangeland and Wildlife Ecology ABSTRACT INVASION BY A NATIVE GRASS: IMPLICATIONS OF INCREASED DOMINANCE OF HETEROPOGON CONTORTUS (TANGLEHEAD) FOR GRASSLAND BIRDS (May 2013) Brian J. Bielfelt, B.S., Florida State University Chairman of Committee: Dr. Andrea R. Litt Heteropogon contortus (tanglehead) is a native grass that has recently spread and become dominant on clay loam soils of southern Texas, leading some land managers to suggest this plant has become invasive. We sought to quantify effects of H. contortus dominance on plant and grassland bird communities in summer and winter 2011-2012 and to determine if responses are similar between seasons. Presence and cover of most species of plants decreased with increased dominance of H. contortus, but structure was taller, denser, and more homogenous than areas with minimal to no H. contortus. Presence and density of Scissor-tailed Flycatcher and presence of Brown-headed Cowbird decreased with H. contortus, whereas presence or density of Mourning Dove, Cassin’s Sparrow, Lark Sparrow, and Eastern Meadowlark increased in summer. Responses of wintering grassland birds generally were negative, with a few species increasing in presence or density. Based on changes we observed in the plant community, H. contortus could be considered an invasive species. Further, we advocate a holistic approach to studying the effects of invasive plants on avifauna because birds have different habitat requirements within each season, resulting in season-specific responses. - iii DEDICATION I dedicate this thesis first and foremost, to my rock and my salvation, Jesus Christ. In the hard times, through the difficult fieldwork, challenging writing, and coursework all I could do is look up for help. I could have not done any of this without His wisdom and guidance. Second, to my wife Melissa, who abandoned stability and comfort in order to support the completion of my thesis. She was always there, encouraging me to press on to the finish line. Finally, to my daughter Autumn ‘Iolana, who has replaced the time I spent working on this thesis. She has my heart. iv ACKNOWLEDGEMENTS I would like to thank my advisor Dr. Andrea Litt for her guidance and support; she took a holistic approach to advising because she was concerned about the thesis work and my family’s personal life. Thank you to my committee Dr. Fred Bryant, Dr. Leonard Brennan, and Thomas Langschied for bestowing their knowledge upon me. A special thanks to Aaron Tjelmeland for his continued help during the project and his enduring friendship. In addition, I would like to thank Forrest Smith for the many hours he patiently helped identify plants and Eric Redeker for his GIS support. Thank you to my funding sources, which made this research possible, including the Rotary Club of Corpus Christi (Harvey Weil Sportsman Conservation Award), the George and Mary Josephine Hamman Foundation, and Texas A&M University - Kingsville (University Research Award). I would like to thank the staff of the Caesar Kleberg Wildlife Research Institute for their help in negotiating the many complicated rules. Thanks also to the undergraduates who helped with this project, especially Celeste Lacy, Taylor Garrison, Matthew Cruz, and Lea Garcia. Many thanks to my wife for many hours of assisting in editing my writing and conducting fieldwork with me, despite the numerous snakes. Finally, I would like to thank Dick and Whit Jones whose generosity and interest in research aided all aspects of my thesis; I regard them as the most respected stewards of wildlife in the region. v TABLE OF CONTENTS Page ABSTRACT .............................................................................................................................. …iii DEDICATION.. ............................................................................................................................ iv ACKNOWLEDGEMENTS… ....................................................................................................... v TABLE OF CONTENTS… .......................................................................................................... vi LIST OF FIGURES… ................................................................................................................... x LIST OF TABLES ........................................................................................................................ xi CHAPTER I: INCREASED DOMINANCE OF A NATIVE GRASS IN GRASSLANDS: DOES BEHAVIOR AND EFFECTS JUSTIFY TERMING HETEROPOGON CONTORTUS AS INVASIVE?.. ............................................................................................. 1 ABSTRACT.. ................................................................................................................................. 1 INTRODUCTION.. ....................................................................................................................... 1 STUDY AREA.. ............................................................................................................................ 4 METHODS… ................................................................................................................................ 6 Plot Selection… .......................................................................................................................... 6 Plant Community Sampling… ................................................................................................... 6 Plant Sub-communities and Soil Sampling ................................................................................ 7 ANALYSIS .................................................................................................................................... 7 Plant Community ........................................................................................................................ 7 Plant Sub-communities and Soil ................................................................................................ 9 RESULTS ...................................................................................................................................... 9 Species-Specific Results… ........................................................................................................ 9 Plant Community ...................................................................................................................... 10 Plant Sub-communities and Soil .............................................................................................. 12 DISCUSSION .............................................................................................................................. 12 Similarities between H. contortus and Nonnative Invasive Plants ......................................... 12 Effects of H. contortus on the Plant Community .................................................................... 14 vi Soils ......................................................................................................................................... 15 Precipitation and H. contortus ................................................................................................. 16 Implications for Wildlife ......................................................................................................... 17 CONCLUSIONS.......................................................................................................................... 17 LITERATURE CITED ................................................................................................................ 18 CHAPTER II: HOME ON THE RANGE OR HABITAT LOST? RESPONSE OF GRASSLAND BIRDS TO INCREASED DOMINANCE OF HETEROPOGON CONTORTUS ......................................................................................................................... 33 ABSTRACT ................................................................................................................................. 33 INTRODUCTION ....................................................................................................................... 34 STUDY AREA ............................................................................................................................ 36 METHODS .................................................................................................................................. 37 Plot Selection ............................................................................................................................ 37 Vegetation Sampling ................................................................................................................ 38 Motte Sampling ....................................................................................................................... 38 Avian Sampling ........................................................................................................................ 39 ANALYSIS .................................................................................................................................. 39 RESULTS ...................................................................................................................................