A MONOGRAPH OF THE GENUS CHORDEILES SWAIN- 

 SON, TYPE OF A NEW FAMILY OF GOATSUCKERS. 



By Harry C. Oberholser, 

 Of the Biological Survey, United States Department of Agriculture. 



INTRODUCTION. 



The present study of the Caprimulgine genus Chordeiles found 

 its origin in the attempt to identify the nighthawks of Texas. It 

 soon became evident that nothing short of a thorough revision of 

 the two North American species, GhordeUes virginianus and Chor- 

 deiles acutipennis, would produce anything like satisfactory results. 

 This was finally undertaken, partly at the instance of Mr. Robert 

 Ridgway ; and the only other species of the genus, Chordeiles rwpes- 

 tris, has been included for the sake of completeness. By reason 

 of the complicated and almost infinite variations due to sex, age, 

 individuals, and geographic areas, the present group is one of the 

 most difficult of all North American birds; and its elucidation has 

 involved the expenditure of an incredible amount of time and labor. 



The material available consists altogether of 1,165 specimens, 

 including the types of most of the valid forms (excepting Chordeiles 

 virginianus virginianus, Chordeiles virginianus aserriensis, Chor- 

 deiles virginiamMs minor, Chordeiles acutipennis acutipennis, Chor- 

 deiles acutipennis exilis, and Chordeiles rupestris rupesfris), and of 

 one synonym, Chordeiles gundlachii Lawrence. These specimens are 

 distributed among the three species as follows: Chordeiles virgini- 

 anus, 780 ; Chordeiles acutipennis, 379 ; Chordeiles rupestris, 6. 



This material has been derived from the following sources: The 

 United States National Museum, including the Biological Survey 

 collection ; the American Museum of Natural History ; the Academy 

 of Natural Sciences of Philadelphia ; the Museum of Comparative 

 Zoology in Cambridge, Massachusetts, including the collection of 

 Messrs. E. A. and O. Bangs; the Carnegie Museum of Pittsburgh, 

 Pennsylvania ; the Museimi of Vertebrate Zoology in Berkeley, Cali- 

 fornia; the Field Museum in Chicago, Illinois; the Victoria Memo- 

 rial Museum in Ottawa, Ontario; and the private collections of 

 Mr. Joseph Grinnell, Mr. F. Seymour Hersey, Dr. G. C Rinker, 



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