< Page:Popular Science Monthly Volume 77.djvu
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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 movements 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 ambiguously called "parasitism," could never become very popular or widespread, 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 disturbance 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 (Molothus badius), described by Hudson, which commonly wastes its eggs, scattering them in all directions, yet it will steal a nest upon

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