Because, soon after the young cuckoo is hatched by the hedge-sparrow, the eggs, or the young ones, whichever should happen to be in the nest, are turned out of it by the cuckoo, and by it alone ; to effect which, the cuckoo is conjectured to have this peculiar conformation of the back.
[We quote this observation from a paper by Dr. Jen-ner, in the Philosophical Transactions for 1788 ; premising the anomaly of the cuckoo laying its eggs in other birds' nests, to be familiar to the reader. We have not space to pursue the subject further, neither will the details of a controversy be looked for in the present work. Mr. Jennings has sensibly observed - " The truth seems to be, notwithstanding all that has been observed and published concerning the cuckoo, that its natural history is still involved in considerable obscurity."]
Till lately, it was not known that any bird laid its eggs in the nests of other birds, besides the cuckoo; it is now, however, well ascertained, that the American cowpen, or cow-bunting, lays its eggs in other birds' nests, and takes no care whatever of its offspring. - Jennings.
Because the cuckoo, seldom seen in company with his mate, even during the breeding season, is, to all appearance, equally solitary at the period of migration.
Because from that bird has been derived the minor scale, whose origin has puzzled so many; the cuckoo's couplet being the minor third sung downwards. - Mag. Nat. Hist.