California Gnatcatcher
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OrnithologicalMonographs No.42 SpeciationandGeographic Variation in Black-tailedGnatcatchers JonathanL. Atwood SPECIATION AND GEOGRAPHIC VARIATION IN BLACK-TAILED GNATCATCHERS ORNITHOLOGICAL MONOGRAPHS This series,published by the American Ornithologists'Union, has been estab- lished for major papers too long for inclusion in the Union's journal, The Auk. Publication has been made possiblethrough the generosityof the late Mrs. Carll Tucker and the Marcia Brady Tucker Foundation, Inc. Correspondenceconcerning manuscripts for publication in the seriesshould be addressed to the Editor, Dr. David W. Johnston, 5219 Concordia St., Fairfax, Virginia 22032. Copies of Ornithological Monographs may be ordered from the Assistant to the Treasurer of the AOU, Frank R. Moore, Department of Biology, University of Southern Mississippi, Southern Station Box 5018, Hattiesburg, Mississippi 39406. (See price list on back cover.) Ornithological Monographs, No. 42, viii + 74 pp. Editor, David W. Johnston Special Reviewers for this issue, Lloyd F. Kiff, Western Foundation of Vertebrate Zoology, 1100 Glendon Ave., Los Angeles,California 90024; Robert M. Zink, Museum of Zoology, Louisiana State University, Baton Rouge, Louisiana 70803. Author, Jonathan L. Atwood, Department of Biology, University of Cal- ifornia, Los Angeles, California 90024 and Mahomet Bird Observa- tory, Box 936, Mahomet, Massachusetts02345. First received, 12 December 1986; final revision completed, 13 October 1987 Issued March 29, 1988 Price $10.00 prepaid ($8.00 to AOU members). Library of CongressCatalogue Card Number 88-70367 Printed by the Allen Press,Inc., Lawrence, Kansas 66044 Copyright ¸ by the American Ornithologists'Union, 1988 ISBN: 0-943610-53-2 SPECIATION AND GEOGRAPHIC VARIATION IN BLACK-TAILED GNATCATCHERS BY JONATHAN L. ATWOOD Department of Biology University of California Los Angeles, California 90024 and Manomet Bird Observatory Box 936 Manomet, Massachusetts 02345 ORNITHOLOGICAL MONOGRAPHS NO. 42 PUBLISHED BY THE AMERICAN ORNITHOLOGISTS' UNION WASHINGTON, D.C. 1988 TABLE OF CONTENTS LIST OF FIGURES ..............................................................................................................................................................vi LIST OF TABLES ...................................................................................................................................................................vii LIST OF APPENDICES ................................................................................................................................................vii INTRODUCTION .................................................................................................................................................................1 GOALS OF THE STUDY ..............................................................................................................................................1 NOMENCLATURAL HISTORY .............................................................................................................................1 MATERIALS AND METHODS .........................................................................................................................4 MORPHOLOGICAL ANALYSES ...........................................................................................................................5 BIOMETRIC ANALYSES ...............................................................................................................................................8 VOCAL ANALYSES ..........................................................................................................................................................9 RESULTS ...........................................................................................................................................................................................10 GEOGRAPHIC AND ECOLOGICAL DISTRIBUTION ........................................................................10 Polioptila californica ..................................................................................................................................10 Polioptila melanura ....................................................................................................................................13 Polioptila nigriceps....................................................................................................................................... 17 AREAS OF SYMPATRY BETWEEN POLIOPTIL•I MELANURA AND P. CAL1- FORNICA ........................................................................................................................................................................17 Palm Springs, Riverside Co., California ..........................................................................18 Valle de Trinidad, Baja California, Mexico ................................................................18 Bahia San Luls Gonzaga(and vicinity), Baja California,Mexico .... 18 "San Felipe Canyon," San Diego Co., California ...............................................19 BREEDING BIOLOGY ....................................................................................................................................................21 VOCAL Dilqq•RENCES AND REPRODUCTIVE ISOLATION ....................................................22 Comparison of major vocalizations .......................................................................................22 Vocal playback experiments ............................................................................................................30 MORPHOLOGICAL VARIATION ........................................................................................................................31 Secondary sexual variation ................................................................................................................31 Relative variability ......................................................................................................................................33 Character correlations and redundancy ............................................................................38 Univariate character analyses ......................................................................................................38 Geographicheterogeneity among characters................................................. 38 Geographic patterns of character variation ....................................................39 Multivariate analyses .................................................................................................................................50 Inter- and intraspecific variation .................................................................................50 Potential hybrid specimens................................................................................................. 56 DISCUSSION ................................................................................................................................................................................59 SPECIESLIMITS AND TAXONOMY ..............................................................................................................59 COMMON NAMES ...........................................................................................................................................................63 HISTORICAL BIOGEOGRAPHY ............................................................................................................................63 ACKNOWLEDGMENTS ............................................................................................................................................66 SUMMARY ...................................................................................................................................................................................67 LITERATURE CITED ....................................................................................................................................................68 LIST OF FIGURES Figurel. Approximate geographicdistributions of Polioptila melanura, P. californica, and P. nigriceps........................................................................................................... 2 2. Groupings of specimensofPolioptila melanura into sample areas for analysis ............................................................................................................................................................6 3. Groupings of specimensof Polioptda californica and P. nigriceps into sample areas for analysis .....................................................................................................7 4. Categoriesused in analysis of variation in tail spot shape ...................7 5. Polioptila caHfornica habitat in coastal southern California and Baja California north of 30øN latitude ............................................................................11 6. Polioptila californica habitat in the Vizcaino desertof central Baja California ................................................................................................................................................................12 7. Polioptila californica habitat in the Cape region of Baja California 12 8. Polioptda melanura habitat in the Sonoran desert of southeastern California and northwestern Baja California ..........................................................14 9. Polioptila melanura habitat in the Sonoran