Shiny Cowbird 



Molothrus bonariensis (Gmelin) 

 Discussion 



As stated in the introductory pages of this report, there is no pressing 

 need for a complete, new, annotated catalog of the victims of this 

 wide-ranging cowbird of South America: there has not been such a 

 demand as has been expressed in the case of the brown-headed and 

 the bronzed species of North America. The original host list given 

 in my 1929 book, the various supplements to it, and the new material 

 now presented, are here brought together and summarized in tabular 

 form, but written accounts are given only for the additional hosts 

 and for those in which significant new information alters or extends 

 our earlier estimates of them as cowbird victims. In the table, the 

 nomenclature of all the earlier publications has been brought into 

 agreement with current usage. 



In the decades since my 1929 book, disappointingly little has been 

 added to many aspects of our knowledge of the breeding habits of the 

 shiny cowbird and of the main features of its host relationships. 

 There seems, therefore, to be little need to elaborate upon many of 

 the statements made in my earlier publication, and only topics that 

 have been developed since or that were not adequately treated then 

 will be discussed here. The newer record data are given chiefly in 

 connection with the individual host species involved. In addition to 

 the following discussion the reader interested in reviewing the over-all 

 picture should consult pages 81-91 of my 1929 description of the sub- 

 ject, and pages 91-121 for the accounts of the hosts known at that 

 time. 



Imperfections in Host Relations 



Apart from some important differences in its choice of hosts, as 

 already discussed in the present report (pp. 9-10), the shiny cowbird 

 is essentially similar in its brood parasitism to the better known 

 brown-headed species, but it does exhibit one imperfection in its 

 breedmg habits that has not been found in its more advanced northern 

 relative. Since this affects its host relations, it merits discussion here. 



The fecundity of the shiny cowbird is less closely and less accurately 

 geared to the availability of potential hosts than is that of its North 

 American counterpart. In his pioneer work in Argentina in the 

 1860's, Hudson noted that the shiny cowbird wasted numbers of its 

 eggs by laying them on the ground and simply leaving them or, not 



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