igi?-] Breeding-habits of the Cuckoo. 189 



The Evolution of the Breeding -habits of the Cuckoo. 



Before dealing with some of the theories and conclusions 

 which have been arrived at regarding the habits of the 

 Cuckoo, it is, I think, of interest to consider by what 

 process of evolution they may have originated, and whether 

 this does not supply us with some clues to the ultimate 

 solution of the mystery. 



The Cuckoo, in reality, is l)y no means so unique as is 

 commonly thought, and it is possible to trace various con- 

 necting links which form a chain, even if incomplete, 

 between the devotion di.s[)layed by most species for their 

 eggs and young, and the almost entire lack of this in the 

 Cuckoo. 



In this respect the Cow-birds {Molothrus) of America 

 are of great interest, for in this family nearly all are 

 parasitic, to a greater or less degres, in their breeding- 

 habits, except the Ray-winged Cow-bird (M. badius), which 

 incubates its eggs, rears its young, and occasionally even 

 builds a nest of its own (as, indeed, do some of the Cuckoos), 

 though usually appropriating those of otlier species. In this 

 family, indeed, we seem to have a much more complete 

 chain than in the Cuckoos, and here also one species has 

 preserved the parental instinct more or less intact, while 

 others have lost it to an equal extent with C. canorus. 



Now it seems not unreasonable to assume that the first 

 stage in the loss of the parental instinct is to be found in 

 those species which have mainly or entirely ceased to build 

 nests of their own but make use of the deserted abodes of 

 other species, and thus are " parasitical " in this respect. 

 It is worth remarking, however, that in many species which 

 have adopted this habit a certain number of individuals still 

 construct their own nests, and the case of an American 

 si)ecies, Machetornis rixosa, is specially noticeable from the 

 fiict that at times an elaborate sti'ucture is made by the bird 

 itself, but more usually the domed nests of other species 

 are used. 



We have, then, in these species certain individuals who 

 have lost the building instinct, while in others it has per- 



