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PAGE Introduction 476 Acknowledgments 476 Nomenclatural History 477 Materials 478 Diagnoses 478 Coloration 485 Courtship 489 Nest Building 491 Food 493 Skeleton 494 Skull 494 Humerus 499 Pygostyle 502 Sternum 505 Relative Lengths of Bones 505 Leg-trunk Percentages 509 Arm-trunk Percentages 511 Musculature 514 Caudal Muscles 514 Pectoral Muscles 517 Hind Limb Musculature 517 Digestive Tract 517 Origin of the Species 519 Conclusions 521 Summary 524 Bibliography 525

INTRODUCTION

It has generally been assumed that the nomadic waxwings originated under boreal conditions, in their present breeding range, and that they did not undergo much adaptive radiation but remained genetically homogeneous. Also it is assumed that the species were wide ranging and thus did not become isolated geographically to the extent that, say, the Fringillidae did. The assumption that waxwings originated in the northern part of North America or Eurasia may be correct, but it is more probable that the origin was more southerly, perhaps, in northern Mexico, of North America Subsequent to the differentiation of this stock in the south, there was a northerly movement, while certain populations remained behind and underwent an evolution different from the northern group. Since the fossil record does not permit us to say when in geological time the family originated, we must rely on anatomical evidence and the distributional evidence of present-day species to estimate when the family stock had diverged from some unknown group sufficiently to merit the status of a separate family.

ACKNOWLEDGMENTS

It is with pleasure that I acknowledge the guidance received in this study from Professor E. Raymond Hall of the University of Kansas. I am indebted also to Dr. Herbert Friedmann of the United States National Museum for the loan of certain skins, skeletons, and alcoholic material; to Mr. Alexander Skutch, for notes on certain Central American birds; and to Dr. Henry W. Setzer, Mr. George H. Lowery, Jr., Mr. Victor E. Jones, Mr. Victor Housholder, Mr. Alvaro Wille-Trejos, and Mr. Morton F. Davis, for gifts of specimens that have been used in this work. Suggestions and critical comments from Professors Worthie H. Horr, Charles G. Sibley and Edward H. Taylor are gratefully acknowledged. I wish also to thank Mrs. Virginia Unruh for the preparation of the drawings used in this work.

NOMENCLATURAL HISTORY

Most workers prior to 1900 utilized the family name Ampelidae to include waxwings, silky flycatchers, and palm-chats. Ridgway elevated the silky flycatchers to family rank under the name Ptilogonatidae, and assigned the palm-chats to a separate family, the Dulidae.

MATERIALS

The following specimens, numbering 238, and representing each currently recognized species and subspecies, were used in the study, and were supplemented by observation in 1947 on specimens in the United States National Museum.

DIAGNOSES

Family Bombycillidae

Subfamily Ptilogonatinae


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