422 U. S. NATIONAL MUSEUM BULLETIN 211 



the art and become a parasite, probably never will be known, though 

 some interesting theories on the subject have been advanced. Much 

 light is thrown on this subject by Herbert Friedmann (1929) in his 

 study of the South American cowbird, to which the reader is referred. 

 For the benefit of the readers who do not own this interesting and 

 comprehensive book, we shall quote from it freely. 



In his chapter on the origin and evolution of the parasitic habit he 

 writes : 



The evidence points unmistakably to the view that the Cowbirds originally 

 bred in normal fashion and that parasitism is a secondarily acquired habit. The 

 reasons for making this statement are: 



1. The instincts of nest-building and incubation are so universally present in 

 all groups of birds in all parts of the world that it seems likely that this is the 

 primitive condition of the Cowbirds. 



2. All the Cowbird's close relatives are nest-builders; in fact, its family, the 

 Icteridae, is known as a family in which the nest-building instincts reach their 

 pinnacle of development. * * * 



3. Within the genera Agelaioides and Molothrus we find several stages in the 

 evolution of parasitism exhibited by different species. The Bay-winged Cow- 

 bird, A. badius, uses other birds' nests and lays its eggs in them but incubates 

 and rears its own young. Sometimes it makes its own nest. The Shiny Cow- 

 bird, M. bonariensis, is parasitic but has the parasitic habit very poorly developed, 

 wasting large numbers of its eggs. Rarely it attempts to build a nest but in this 

 it is never successful. This indicates that originally it built a nest but no longer 

 knows how. The North American Cowbird, M. ater, is entirely parasitic but is 

 not wasteful of its eggs. * * * 



4. The parasitic Cowbirds (Molothrus) have definite breeding territories and are 

 more or less monogamous. Howard has shown that the territory precedes the 

 nest in the evolution of the instincts of guarding associated with reproduction. 

 If the Cowbirds were parasitic from the very beginning it would be very hard 

 to explain their territorial instincts. * * * The facts that the Cowbirds are 

 fairly monogamous indicates that they were monogamous originally and probably 

 nested in normal fashion as all monogamous birds do. 



5. The most primitive of the existing species of Cowbirds is, * * * the Bay- 

 winged Cowbird. This species is the only one of its group that is not parasitic and 

 doubtlessly represents the original condition of the Cowbird stock. * * * 



From the above it seems safe to assume that parasitism is not the original 

 condition in the history of the Cowbirds. The problem, then is not whether the 

 Cowbirds were always parasitic or not, but how they lost their original habits 

 and became parasitic. * * * 



The best theory advanced as yet, and one which my studies tend to support 

 in part, at least, is that of Prof. F. H. Herrick. This writer studied the cyclical 

 instincts of birds and found that not infrequently different parts of the cycle are 

 interrupted by various causes which result in a general lack of harmony between 

 successive parts of the cycle. He suggested that the parasitic habit may have 

 originated from a lack of attunement of the egg-laying and the nest-building 

 instincts which resulted in the eggs being ready for deposition before a nest was 

 ready for them. * * * 



The first writer to see that one explanation would not serve for all the different 

 groups of parasitic birds was G. M. Allen (1925). * * * Wisely refraining from 

 offering an explanation of parasitism, he suggests several "possible ways of origin." 



