108 mr, w. h. hudson on the [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 exceed- 

 ingly frail platform nests from which the eggs and young very fre- 

 quently 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 be- 

 tween 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 nest- 

 ing-habits of several species, and one remarkable habit of M. bonari- 

 ensis, 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 spe- 

 cies. 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 condi- 

 tions as we find them, unless the conditions themselves were un- 

 varying, 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 (Pitanyus bellicosus) that in winter subsists chiefly on mice 



