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. I 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 anytime. 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 
