Preface 



CowBiRDS are an ideal group in which to study the biology of brood 

 parasitism; within the six included species there are displayed all 

 stages of the development of this mode of reproduction ranging from 

 that of the non-parasitic baj^-wing through those of the completely 

 parasitic screaming, shiny, brown-headed, bronzed, and giant cowbu'ds. 



The present report deals only with their host relationships, as this 

 is the aspect of their biology in which our knowledge has shown the 

 greatest increase since my initial over-all discussion was published in 

 1929. 



It is assumed that the majority of users of this monograph will be 

 interested chiefly in the common North American species, the brown- 

 headed cowbird, MolotJinis ater; accordingly, the more detailed 

 discussion of this buxl is presented first, constituting the major part of 

 the report. This is followed b}^ a shorter but similar treatment of the 

 other North American species, the bronzed cowbird, Tangavius 

 aeneus; then by a discussion of the two South American parasitic 

 species, the shiny cowbird, M. honariensis, and the screaming cowbird, 

 M. rufo-axillaris ; and finally by a discussion of the giant cowbu'd, 

 Psomocolax oryzivorus, of Central and South America. The phj'loge- 

 netic sequence is thus ignored for the interest and convenience of the 

 reader. For a description of the phylogenetic relations of the included 

 species, the reader is referred to pages 343-346 of my 1929 book. I 

 know of no recent information that would cause me to suggest any 

 alteration in the picture presented there, except that which is given in 

 the present discussion of Psomocolax (see pp. 216-222). 



For the two North American species I here submit complete anno- 

 tated catalogs of their hosts, in answer to many requests that have 

 come to me over the years from students and investigators of various 

 ones of the included host birds. In the case of the South American 

 shiny cowbird and the Central American giant cowbird, the unfortu- 

 nate general lack of interest in birds in these areas has made it unneces- 

 sary to produce a similar new host catalog at this time, although our 

 knowledge of the victims of both species has increased as greatly as 

 that of their North American counterparts. Accordingly, I have 

 included a complete tabular outline of the known victims of each of 

 the races of the parasites, but I have written accounts only of newly 

 added hosts and of those others of which our estunates as cowbu'd 

 victims have been altered by recent information. Since there has 



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