Defective Instinct Supplemented. 109 



although they riever sazu them, and perversely throw 

 aside all the instruction of their foster-parents, 

 which they enjoyed oftentimes to the detriment 

 or destruction of the rightful birdlings of the nest. 



We here observe two things that impress us 

 with the blindness as well as certainty with which 

 Instinct operates, when performing those works 

 which often appear so wise. The Cow-bird simply 

 finds a nest, deposits an Qgg and leaves it to its 

 fate. The Instinct of the mother stops there ; and 

 the whole race of Cow-birds would speedily become 

 extinct if this apparently defective Instinct were 

 not supplemented by the Instinct of the foster- 

 mother that broods upon the Qgg as though it were 

 her own, and then feeds the strange bird hatched from 

 it, until it becomes twice her own size, it may be, 

 and entirely unlike her own young. Though this 

 young intruder often pitches all the rightful occu- 

 pants of the nest upon the ground to die, yet the 

 foster-mother does not generally detect the imposi- 

 tion practised upon her. If her Instinct Avere not at 

 fault there would soon be an end of Cow-birds. But 

 if Cow-birds are to exist at all, then the perfection 

 and wisdom manifested in the foster-mother's In- 

 stinct consists in the certainty of her being de- 

 ceived and thus doing for the Cow-bird the work 

 which its parent refused or failed to do for it. 



In a certain sense the nest-building Instinct of 

 birds is connected with the function of producing 

 young ; but the connection is very remote compared 



