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Show 168 MR. W. H. HUDSON ON T H E [Mar. 3, instinct of the Cuckoo (and it probably is favourable) to lay eggs at longer intervals than other species, then natural selection would avail itself of every modification in the reproductive organs that tended to produce such a result, and make the improved structure permanent. It is said (' Origin of Species,' chapter on instinct) that the American Cuckoo lays also at long intervals, and has eggs and young at the same time in its nest, a circumstance manifestly disadvantageous. Of the Coccyzus melanocoryphus, the only one of our three Cuckoos whose nesting-habits I am acquainted with, I can say that it never begins to incubate till the full complement of eggs are laid-that its young are hatched simultaneously. But if it is sought to trace the origin of the European Cuckoo's instinct in the nesting-habits of American Coccyzi, it might be attributed not to the aberrant habit of perhaps a single species, but to another and more disadvantageous habit common to the entire genus, viz. their habit of building exceedingly frail platform nests from which the eggs and young very frequently fall. By occasionally dropping an egg in the deep secure nest of some other bird, an advantage would be possessed by the birds hatched in them, and in them the habit would perhaps become hereditary. Be this as it may (and the one guess is perhaps as wide of the truth as the other), there are many genera intermediate between Cuculus and Molothrus in which no trace of a parasitic habit appears ; and it seems more than probable that the analogous instinct originated in different ways in the two genera. As regards the origin of the instinct in Molothrus, it will perhaps seem premature to found speculations on the few facts here recorded, and before we are acquainted with the habits of other members of the genus. That a species should totally lose so universal an instinct as the maternal one and yet avail itself of that affection in other species to propagate itself, seems a great mystery. Nevertheless I cannot refrain from all conjecture on the subject, and will go so far as to suggest what may have been at least one of the many concurrent causes that have produced the parasitic instinct. The apparently transitional nesting- habits of several species, and one remarkable habit of M. bonariensis, seem to me to throw some light on a point bearing intimately on the subject, viz. the loss of the nest-making instinct in this species. The hypothesis will perhaps be considered very fine-spun indeed; nevertheless, when a larger body of facts have been got together, it may be of some use to future inquirers ; the facts here adduced will also have their value. Instincts vary greatly. It would be almost a truism to say that were it not so they would not be so well adapted to external conditions as we find them, unless the conditions themselves wrere unvarying, which is not the case ; for whilst a species is well adapted to its station in its instincts or inherited habits, it is frequently not so well adapted to them in its relatively inimitable structure. Thus we have in Buenos Ayres a Tringa that avoids the wet, and has all the habits of a strictly upland Plover, a Sparrow (Ammodromus ma-nimbe) with the manners of a reed-loving Synallaxis, likewise a Tyrant (Pitangus bellicosus) that in winter subsists chiefly on mice |
