174 U.S. NATIONAL MUSEUM BULLETIN 233 



centered its attentions on the nests of an allied group, the hangnests 

 of the genus Icterus. It has gradually widened its scope of parasitism 

 to include many other birds, but even today a large percentage of its 

 recorded eggs and young are to be found in the nests or in the care of 

 species of Icterus and related birds. The process has gone far enough 

 to make some of the finches equally acceptable in this respect, as is 

 evidenced by Dickerman's observations on the degree of parasitism 

 inflicted on the song sparrow in Chapultepec Park, Mexico City, and 

 Rowley's report on the frequency with which the rusty-crowned 

 sparrow is victimized in Morelos — as high a local frequency as has 

 been noted for any species of host. 



The data in my 1929 report (p. 328) referred to 76 victimized nests, 

 of which no fewer than 51 belonged to 4 species of Icterus. The 

 present material is more than twice as great — 186 individual records 

 plus an indefinite number that can only be inferred from the use of 

 adjectives such as "common" or "frequent" inserted before the word 

 "host" by the describers. Of the 186, 84 refer to the genus Icterus, 

 9 species of which are now included. In addition, it may be noted 

 that all the hosts described loosely in print or in correspondence as 

 "common" or "frequent" were species of Icterus. The percentage 

 of the total that concerns species of Icterus is less now than in the 1929 

 material, about 45 percent instead of two-thirds. This drop is in 

 part a contrived result, due to the fact that many recent observations 

 on Icterme hosts have not been published because of their repetitive 

 nature while every additional instance of a less frequent host is 

 more apt to be put on record. 



In the present catalog the hosts are discussed as species. How- 

 ever, to make the data as readily usable as possible, I have first 

 tabulated them by subspecies both of the hosts and of the parasite. 

 In this table no column has been left for the Colombian race of the 

 bronzed cowbird, T.a. armenti, for the reason that nothing is known 

 of its hosts. In fact, it is only an assumption, although a likely 

 one, that it is parasitic in its breeding. It will be obvious at a glance 

 that very little is known of the breeding habits of the small southwest 

 Mexican race T.a. assimilis. The fact that none of its 4 known 

 hosts is a species of Icterus should not be assumed to be meaningful; 

 this is probably a matter of insufficient field observation in its range. 

 The greater number of hosts recorded for T.a. aeneus than for T.a. 

 milleri is, again, merely a reflection of differential amounts of study 

 and collecting in their respective habitats. 



Approximately one-third of all the victims have been found to rear 

 the young bronzed cowbirds (at least as far as the fau-ly well-feathered 

 nestling stage). For many of the others, the absence of such records 



