94 THE POPULAR SCIENCE MONTHLY 



hitching its way, thus laden, up the wall of the nest, throws them 

 overboard. If such a bird is replaced after a time, the same move- 

 ments are repeated. With the coast thus clear, the little "parasite" 

 can monopolize the attention of its nurse, and grows apace, being 

 attended with all the care which is bestowed on a legitimate child. 

 As Philemon Holland has quaintly rendered the account of the elder 

 Pliny : 



" And this yong Cuckow being greedy by kind, beguiling the other yong 

 birds and intercepting the meat from them, groweth hereby fat and faire-liking: 

 whereby it comes into speciall grace and favour with the dam of the rest, and 

 nource to it. She joieth to see so goodly a bird toward: and wonders at her 

 selfe that she hath hatched & reared so trim a chick. The rest, which are her 

 owne indeed, she sets no store by, as if they werr changelings: but in regard 

 to that one, counteth them all bastards and misbegotten." Having followed 

 our elder worthy thus far, we should give his sequel also, even if he steps from 

 observation to fable: "yea, and suffereth them to be eaten and devoured of the 

 other even before her face: and this she doth so long, until the yong cuckow 

 being once fledge & readie to flie abroad, is so bold as to seize on the old Titling, 

 and to eat her up that hatched her." 



It is evident that this practise of nest-stealing, somewhat ambigu- 

 ously called " parasitism," could never become very popular or wide- 

 spread, for it would soon break down of its own weight. 



For over two thousand years, or since the time of Aristotle, who 

 was the first to leave a permanent record of this propensity in the 

 European cuckoo, the question has been asked, How could such a habit 

 arise? and the answers have been various, and far from satisfactory. 

 The key to the matter lies, as we believe, in the cyclical instincts, and 

 in the disturbances to which they are prone. When the normal rhythm 

 is generally disturbed or permanently changed, new instincts and even 

 new structures may arise, which serve as a counterbalance to the 

 changes wrought. 



We believe that the instinct of parasitism got its start through lack 

 of attunement in terms 3 and 4, of the reproductive cycle, and that it 

 has passed through essentially the following stages: (1) The egg 

 forthcoming before there is a nest ready to receive it, a condition 

 sporadic in very many, if not in most modern birds, due to unknown 

 causes, such as lead to a premature growth of the ovary, or to a dis- 

 turbance of certain instincts. There is a loss of eggs, although a nest 

 may be eventually built, and young reared in the season. (2) The 

 eggs are ready before the nest, and many are lost by dropping them 

 on the ground, while others are laid in stolen nests. A proper nest is 

 sometimes built, but whether young are ever reared, will depend upon 

 circumstances. This stage is exemplified by the Argentine cowbird 

 (MolotJius badius), described by Hudson, which commonly wastes its 

 eggs, scattering them in all directions, yet it will steal a nest upon 



