90 The Naturalist in La Plata. 



as from the parent bird. But if while being thus 

 fed the parent returns and emits the warning note, 

 they instantly cease their hunger-cries, close their 

 gaping mouths, and crouch down frightened in the 

 nest. This fear caused by the parent bird's warn- 

 ing note begins to manifest itself even before the 

 young are hatched — and my observations on this 

 point refer to several species in three widely 

 separated orders. "When the little prisoner is 

 hammering at its shell, and uttering its feeble peep, 

 as if begging to be let out, if the warning note 

 is uttered, even at a considerable distance, the 

 strokes and complaining instantly cease, and the 

 chick will then remain quiescent in the shell for 

 a long time, or until the parent, by a changed note, 

 conveys to it an intimation that the danger is over. 

 Another proof that the nestling has absolutely no 

 instinctive knowledge of particular enemies, but is 

 taught to fear them by the parents, is to be found 

 in the striking contrast between the habits of para- 

 sitical and genuine young in the nest, and after they 

 have left it, while still unable to find their own 

 food. 1 have had no opportunities of observing the 

 habits of the young cuckoo in England with regard 

 to this point, and do not know whether other ob- 

 servers have paid any attention to the matter or 

 not, but I am very familiar with the manners of the 

 parasitical starling or cow-bird of South America. 

 The warning cries of the foster parent have no effect 

 on the young cow-bird at any time. Until they are 

 able to fly they will readily devour worms from the 

 hand of a man, even when the old birds are hover- 

 ing close by and screaming their danger notes, and 



