Movements, Populations, and Habitat Preferences of Three Species of Pocket Mice (Perognathinae) in the Big Bend Region of Texas
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Special Publications Museum of Texas Tech University Number 58 July 2011 MOVE M ENTS , PO P ULATIONS , AND HABITAT PREFERENCES OF TH REE SP ECIES OF POCKET MICE (PEROGNAT H INAE ) IN T H E BIG BEND REGION OF TEXAS RICHA R D D. PO R TE R CALVIN A. PO R TE R , EDITO R Front cover: Background photograph is the Merriami plot at Panther Junction, looking southwest towards the Chisos Mountains (May 2011). Lower center inset: Perognathus merriami. Left insets: Chaetodipus eremicus and the Eremicus plot (May 2008) looking southwest. Right insets: Chaetodipus nelsoni and the Nelsoni plot (May 2008) looking northwest with Nugent Mountain on the left. The arrangement of the photographs represents the ecological distribution of the three species of pocket mice in Big Bend. Chaetodipus eremicus commonly occupies flat, open, rock-free sandy or loamy areas, while C. nelsoni is found most commonly in steep, rocky, and often densely vegetated habitats. Perognathus merriami can occupy a wide range of habitats, but in the presence of the larger Chaetodipus species is most abundant in habitats intermediate to those occupied by C. nelsoni and C. eremicus. Pocket mouse photographs were taken during the study by R. D. Porter. Habitat photographs and cover design by C. A. Porter. SPECIAL PUBLICATIONS Museum of Texas Tech University Number 58 Movements, Populations, and Habitat Preferences of Three Species of Pocket Mice (Perognathinae) in the Big Bend Region of Texas RICHA R D D. PO R TE R CALVIN A. PO R TE R , EDITO R Layout and Design: Lisa Bradley Cover Design: Calvin A. Porter Production Editor: Lisa Bradley Copyright 2011, Museum of Texas Tech University This publication is available free of charge in PDF format from the website of the Natural Sciences Research Laboratory, Mu- seum of Texas Tech University (nsrl.ttu.edu). The authors and the Museum of Texas Tech University hereby grant permission to interested parties to download or print this publication for personal or educational (not for profit) use. Re-publication of any part of this paper in other works is not permitted without prior written permission of the Museum of Texas Tech University. This book was set in Times New Roman and printed on acid-free paper that meets the guidelines for permanence and durability of the Committee on Production Guidelines for Book Longevity of the Council on Library Resources. Printed: July 2011 Library of Congress Cataloging-in-Publication Data Special Publications of the Museum of Texas Tech University, Number 58 Series Editor: Robert J. Baker Movements, Populations, and Habitat Preferences of Three Species of Pocket Mice (Perognathinae) in the Big Bend Region of Texas Richard D. Porter Edited by Calvin A. Porter ISSN 0169-0237 ISBN 1-929330-22-7 ISBN13 978-1-929330-22-5 Museum of Texas Tech University Lubbock, TX 79409-3191 USA (806)742-2442 TABLE OF CON T EN T S Foreword (by the Editor) 3 Abstract 8 Introduction 9 Topography and Vegetation of the Study Area 9 Climate of the Study Area 11 Systematic Relationships of Pocket Mice 11 Materials and Methods 14 Preliminary Field Work 16 The Habitat Plots 16 The Population Plots 17 Habitat Analysis Methods 22 Laboratory Examinations 26 Characteristics of the Population Plots 27 Ectoparasites 33 Altitudinal Distribution of Pocket Mice 35 Pocket Mice in Relation to Habitat 36 Distribution and Abundance of Pocket Mice in Relation to Slope 36 Distribution and Abundance of Pocket Mice in Relation to Soil Texture 44 Distribution and Abundance of Pocket Mice in Relation to Rock Content of the Substrate 46 Distribution and Abundance of Pocket Mice in Relation to Vegetation Density 47 Distribution and Abundance of Pocket Mice in Relation to Plant Species 49 Discussion and Comparisons of Habitat Preferences of Pocket Mice 50 1 2 SPE C IAL PUBLI C A T IONS , MUSEU M OF TEXAS TE C H UNIVERSI T Y Pocket Mouse Habitats in the Big Bend Region 52 Sex Ratios 62 Seasonal Activity Patterns 66 Seasonal Abundance 68 Breeding Habits 72 Breeding Season of Merriam’s Pocket Mouse 72 Breeding Season of Nelson’s Pocket Mouse 74 Breeding Season of the Chihuahuan Pocket Mouse 75 Discussion of the Extent of Breeding Season in Pocket Mice 76 Analysis of Numbers and Uterine Distribution of Embryos and Placental Scars 76 Incidence of Breeding in Juveniles 77 Longevity 77 Pelage Changes 79 Spatial Organization 83 Home Range 83 Shift in Center of Activity 87 Dispersal 88 Territoriality 88 Acknowledgments 93 Afterword (by the Editor) 94 Literature Cited 96 Appendix I 102 Appendix II 104 Appendix III 105 POR T ER —EC OLOGY OF PO C KE T MI C E IN T HE BIG BEND REGION 3 FOREWORD Background of the Study also included proposed studies of systematics, diet, and burrow architecture. “As the study progressed,” My father, Richard D. Porter, completed his B.S. he wrote, “the scope of the investigation was reduced at the University of Utah in 1950 and his M.S. in 1952. commensurate with the time available.” The result of His thesis advisor was Dr. William H. Behle, and his this “reduced” two-year field study was a 255-page thesis was entitled The Hungarian Partridge in Utah, dissertation (Porter 1962) which is published here (in with Special Reference to Ecology and Life History edited form) for the first time. The study was funded by (Porter 1951, 1955). He worked for two years as an the Texas Game and Fish Commission under contract ecologist at Dugway Proving Grounds before enrolling with the Texas Agricultural Experiment Station. In in a Ph.D. program at the Agricultural and Mechani- addition to pocket mice and other mammals, my father cal College of Texas (now Texas A&M University) collected birds, reptiles, amphibians, and parasitic in 1955. His doctoral program was directed by Dr. arthropods (Wiseman 1959; Eads 1960; Degenhardt William B. Davis. 1966; Wauer 1969, 1973a, c; Fleet and Dixon 1971), and conducted population surveys of deer, all as part Upon completing his course work in June 1957, of the larger project that funded the research. Speci- my father moved with his family to Big Bend National mens collected during the study are now deposited in Park (BBNP) for more than two years, during which collections at BBNP, Texas A&M University, Brigham time he conducted field work on the ecology of pocket Young University, the Smithsonian Institution, and mice (Plate 1). He compiled more than 18,000 trap elsewhere. During the study, he collected two previ- nights and carefully recorded data about vegetation, ously undescribed species of fleas (Eads 1960), three soil, habitats, movements, reproductive condition, species of undescribed mites (discussed in this study), parasites, pelage, and other life history characteristics. and four undescribed species of avian chewing lice This ambitious effort was just a portion of the study (Wiseman 1959). originally envisioned. The original research prospectus Plate 1. The author, Richard D. Porter, in Big Bend National Park, ca. January 1959. Photographer unknown. 4 SPE C IAL PUBLI C A T IONS , MUSEU M OF TEXAS TE C H UNIVERSI T Y An accomplished photographer, my father took Whitewater. During his first year at Whitewater, he put hundreds of photographs of the habitat, flora, and fauna the finishing touches on the dissertation, and returned to of BBNP. Many of his photographs were included in College Station in July 1962 to defend the dissertation. the second edition of The Mammals of Texas (Davis The degree was awarded in August 1962 1960) and some still appear in the current sixth edition (Schmidly 2004). Other Big Bend photographs were After leaving Whitewater in 1965, my father published in Naturalist’s Big Bend (Wauer 1973b, 1980; taught biology at the New Mexico Institute of Mining Wauer and Fleming 2002) and Birds of Utah (Hayward and Technology. In 1967, he began work for the U. S. et al. 1976). Several were displayed for many years at Fish and Wildlife Service, first at the Patuxent Wild- Park Headquarters. life Research Center near Laurel, Maryland, and then (beginning in 1973) for the Denver Wildlife Research While conducting field work, he resided with his Center, stationed in Provo, Utah. At Patuxent, he family in a trailer at Panther Junction. My mother, Lois performed research (e.g., Porter and Wiemeyer 1969, Gunderson Porter, was hired as the Park’s schoolteacher 1972; Wiemeyer and Porter 1970) on the effects of (Tucker 2008), and taught grades 1-8 in a single class- DDT and other pesticides on American Kestrels (Falco room in the small San Vicente School at Panther Junc- sparverius). His work at Provo involved ecological tion. For much of her tenure, she was the only teacher surveys of raptors, particularly the Peregrine Falcon in the Park. My father was employed for $25 per (Falco peregrinus) in the western United States and month as the school custodian. My mother frequently Baja California (e.g., Porter and White 1973, 1977; assisted with his research, particularly with trapping, Porter et al. 1988). He retired from the Fish and Wild- substrate analysis, and recording data in the field. My life Service in 1980, and spent his retirement in Maple- brothers Sanford (now a USDA research entomologist ton and Brigham City, Utah, and finally Gainesville, in Gainesville, Florida) and Neil (who died at age 6 in Florida. He died in Gainesville on 2 October 2007 at a tragic accident in August 1961) ranged in age from 2 the age of 84. to 5 during the study, and often accompanied my father into the field while my mother was in the classroom. I Impact of the Study was born in August 1959 as the field study concluded.