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Rio Grande Beaver (Castor Canadensis Mexicanus) Survey in Big Bend National Park

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Rio Grande Beaver (Castor Canadensis Mexicanus) Survey in Big Bend National Park RIO GRANDE BEAVER (CASTOR CANADENSIS MEXICANUS) SURVEY IN BIG BEND NATIONAL PARK by Howland J. Reich IV, B.S. A thesis submitted to the Graduate Council of Texas State University in partial fulfillment of the requirements for the degree of Masters of Science with a Major in Wildlife Ecology May 2015 Committee Members: Thomas R. Simpson, Chair Floyd W. Weckerly M. Clay Green COPYRIGHT by Howland J. Reich IV 2015 FAIR USE AND AUTHOR’S PERMISSION STATEMENT Fair Use This work is protected by the Copyright Laws of the United States (Public Law 94-553, section 107). Consistent with fair use as defined in the Copyright Laws, brief quotations from this material are allowed with proper acknowledgement. Use of this material for financial gain without the author’s express written permission is not allowed. Duplication Permission As the copyright holder of this work I, Howland J. Reich IV, authorize duplication of this work, in whole or in part, for educational or scholarly purposes only. ACKNOWLEDGMENTS Thank you to all my friends and family, for all their encouragement throughout this entire process. They were truly my support and motivation through these last few years. I thank my parents for all their generosity, love, and advice. I cannot express in words the gratitude I have for Dr. Thomas R. Simpson, my major advisor. I thank him for all his support, dedication, and motivation. Without the numerous days spent in the field, it would not have been possible to complete this thesis. I would also like to thank my other committee members, Dr. Floyd W. Weckerly and Dr. M. Clay Green. This thesis would not have been possible without Dr. Weckerly’s help with statistical analysis and Dr. Green’s help with GIS mapping. They have both played a tremendous role in my success in graduate school. Thanks to everyone who helped me collect data out in the field. A very special thanks goes to Sam Frantzen, who spend numerous weeks with me floating the river in Big Bend National Park. I also want to thank Colton Robbins, Westley Collins, Hope Hernandez, Natalie Craig, Frances Rapier, and Phillip Allison for all their help collecting data. I would also like to thank Raymond Skiles, the Wildlife Biologist in Big Bend National Park, for making this thesis possible. iv TABLE OF CONTENTS Page ACKNOWLEDGMENTS ................................................................................................. iv LIST OF TABLES ............................................................................................................. vi LIST OF FIGURES .......................................................................................................... vii ABSTRACT ..................................................................................................................... viii CHAPTER I. INTRODUCTION ................................................................................................1 II. STUDY SITE ......................................................................................................7 III. MATERIALS AND METHODS .....................................................................10 GIS Mapping ..............................................................................................10 Camera Trapping .......................................................................................11 Live Trapping.............................................................................................13 IV. RESULTS ........................................................................................................16 River Survey and Habitat Mapping of the Rio Grande River in Big Bend National Park .............................................................................16 Vegetation and Foraging Activity ..............................................................23 Beaver Population Estimates .....................................................................24 Live Trapping.............................................................................................25 V. DISCUSSION ...................................................................................................26 Foraging Activity .......................................................................................28 Live Trapping.............................................................................................30 VI. FUTURE MONITORING ...............................................................................32 APPENDIX SECTION ......................................................................................................33 LITERATURE CITED ......................................................................................................41 v LIST OF TABLES Table Page 1. River survey of the Rio Grande River in Big Bend National Park with the dates of survey, location of survey, length of river surveyed, number of active dens, and the number of colonies found .................................................16 2. Gage height and discharge recordings from the USGS gage on the Rio Grande River near Castolon, Tx for the dates of river survey (U.S. Geological Survey, 2012) .............................................................................17 3. Water depth found at the entrance of beaver dens and the number of dens associated with each water depth ...........................................................................18 4. Food Species of C. Canadensis Mexicanus based on cuttings in Big Bend National Park, Texas ..............................................................................................23 5. Beaver colonies along the Rio Grande River in Big Bend National Park ...................33 6. Random sample locations with maximum depth found in buffer ................................36 7. Minimum and Maximum number of beaver estimated at each of the surveyed colonies with the number of camera trapping nights ..............................39 8. GPS location of nutria activity in Big Bend National Park, Texas ..............................40 vi LIST OF FIGURES Figure Page 1. GIS map of the study site in Big Bend National Park ...................................................9 2. Custom build live trap was used to trap beaver in Big Bend National Park ................15 3. GIS map of the western half of the study site, Terlingua Creek to Mariscal Canyon, in Big Bend National Park with beaver colonies.....................................19 4. GIS map of the eastern half of the study site, Mariscal Canyon to Boquillas Canyon, in Big Bend National Park, Texas with beaver colonies, 2013 ........................................................................................................19 5. GIS map of beaver colonies from the mouth of Terlingua Creek to Black Dike ........................................................................................................................20 6. GIS map of beaver Colonies from Black Dike to Woodsons ......................................20 7. GIS map of beaver colonies from Woodsons to Solis .................................................21 8. GIS map of beaver colonies from solis to Gravel Pit ..................................................21 9. GIS map of beaver colonies from Gravel Pit to Boquillas Canyon .............................22 10. Example section of the completed GIS map, (mouth of Terlingua Creek), with all layers (list the layers) for Big Bend National Park, Texas, 2013........................................................................................................................22 vii ABSTRACT The Rio Grande River forms the 176 km boundary of Big Bend National Park with Mexico and is home to the southwestern subspecies of North American beaver, Castor canadensis mexicanus. The last survey for the Rio Grande beaver, sometimes known as the Mexican beaver, in Big Bend National Park was conducted in 1981 by P. Strong and J. Bissonette. Our objectives were to document centers of beaver activity and estimate the population of beaver in Big Bend National Park. We surveyed the Rio Grande River on float trips with kayaks and canoes from the mouth of Terlingua Creek to the mouth of Boquillas Canyon. We recorded water depth, type of vegetation, sign of active beaver colonies (presence of dens, beaver tracks, scat, and cuttings), and ranked the amount of beaver activity within each colony as high, medium or low. From these data, we created a map using ArcGIS showing bathymetry of the river, vegetation profiles, and active beaver sign. We delineated a total of 98 active beaver colonies in the study area occupying deeper pools along the Rio Grande. We conducted camera surveys on 11 of the colonies to estimate the number of beaver in each colony. With camera survey data and activity ranking of each colony, we estimated a population of 185 beavers occupying the 98 colonies. This represents a 38% increase in the beaver population along the Rio Grande since 1981. viii I. INTRODUCTION The North American beaver (Castor canadensis) is a large semi-aquatic rodent of the family Castoridae. The family is represented by one genus with two species, C. canadensis in North America, and C. fiber in Eurasia. Twenty-four subspecies were originally described in North America for C. canadensis, but their current status and distribution are confused in many parts of the United States by reintroductions of beavers from source populations different from the original subspecies (Wilson and Ruff, 1999). Subspecies were presumably originally segregated by
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