INSTINCTS OF BIRDS. 867 



and stability ; but the undeniable fact, that 

 birds when taken very young, even before they 

 can see, and brought up in confinement, do 

 sometimes construct nests, is alone sufficient to 

 refute this opinion. 



The sparrow-hawk and kestril often make use 

 of the deserted habitation of the magpie as a 

 receptacle for their eggs, and the sparrow fre- 

 quently takes forcible possession of the rustic 

 dwelling of the house-martin for the same pur- 

 pose. Why then are they never known to build 

 nests similar to those which they thus appro- 

 priate to themselves? and why does not the 

 cuckoo, which is always brought up in the 

 nest of some other bird, construct one itself?* 

 The reason is obvious : the act of nidification 

 is not regulated by observation or instruction, 

 but is under the immediate direction of instinct. 



Guided by this mysterious power, individuals 

 of the same species, under like circumstances, 

 always adhere to the same stile of architecture. 

 Thus, some of the smaller birds, which produce 

 a large number of eggs, constantly make the 



* I have pointed out the errors into which Dr. Darwin has 

 fallen in his remarks on the cuckoo, in my observations dn 

 that bird, printed in the fourth volume of the new series of the 

 Society's Memoirs. 



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