200 INSTINCTS OF THE MOLOTHRUS. [CHAI>. VIE. 



Ramsay, to an extraordinary degree in colour; so that in this 

 respect, as well as in size, natural selection might have secured 

 and fixed any advantageous variation. 



In the case of the European cuckoo, the offspring of the foster- 

 parents are commonly ejected from the nest within three days 

 after the cuckoo is hatched ; and as the latter at this age is in 

 a most helpless condition, Mr. Gould was formerly inclined to 

 believe that the act of ejection was performed by the foster- 

 parents themselves. But he has now received a trustworthy 

 account of a young cuckoo which was actually seen, whilst still 

 blind and not able even to hold up its own head, in the act of 

 ejecting its foster-brothers. One of these was replaced in the 

 nest by the observer, and was again thrown out. With respect to 

 the means by which this strange and odious instinct was acquired, 

 if it were of great importance for the young cuckoo, as is probably 

 the case, to receive as much food as possible soon after birth, I 

 can see no special difficulty in its having gradually acquired, 

 during successive generations, the blind desire, the strength, and 

 structure necessary for the work of ejection; for those young 

 cuckoos which had such habits and structure best developed 

 would be the most securely reared. The first step towards the 

 acquisition of the proper instinct might have been mere uninten- 

 tional restlessness on the part of the young bird, when somewhat 

 advanced in age and strength ; the habit having been afterwards 

 improved, and transmitted to an earlier age. I can see no more 

 difficulty in this, than in the unhatched young of other birds 

 acquiring the instinct to break through their own shells; or 

 than in young snakes acquiring in their upper jaws, as Owen has 

 remarked, a transitory sharp tooth for cutting through the tough 

 egg-shell. For if each part is liable to individual variations at all 

 ages, and the variations tend to be inherited at a corresponding or 

 earlier age, propositions which cannot be disputed, then the 

 instincts and structure of the young could be slowly modified as 

 surely as those of the adult ; and both cases must stand or fall 

 together with the whole theory of natural selection. 



Some species of Molothrus, a widely distinct genus of American 

 birds, allied to our starlings, have parasitic habits like those of the 

 cuckoo; and the species present an interesting gradation in the 

 perfection of their instincts. The sexes of Molothrus badius are 

 stated by an excellent observer, Mr. Hudson, sometimes to live 

 promiscuously together in flocks, and sometimes to pair. They 

 either build a nest of their own, or seize on one belonging to some 

 other bird, occasionally throwing out the nestlings of the stranger. 

 They either lay their eggs in the nest thus appropriated, or oddly 

 enough build one for themselves on the top of it. They usually 

 sit on their own eggs and rear their own young ; but Mr. Hudson 



