BIRDS AS AUTOMATA 105 



On this hypothesis alone are many of the actions of 

 nesting birds comprehensible. 



That the construction of the nest is in the main an 

 instinctive habit and not the result of intelligence is 

 proved by the fact that a bird which has been hatched 

 out in an incubator will, at the appointed season, build 

 a nest. If birds were not guided by instinct they would 

 never take the trouble to do such a quixotic thing. 

 What benefit can they derive from laboriously collecting 

 a number of twigs and weaving them into a nest? 



It is, of course, natural selection that has originated 

 this instinct ; for those species in which the parental 

 instinct is not developed, or in which there is not some 

 substitute for it, must inevitably perish. When once 

 this instinct has taken root natural selection will tend 

 to perpetuate it, since those species which take the 

 best care of their young are those which are likely to 

 survive in the struggle for existence. 



Many instances can be adduced to show how auto- 

 matic are the actions of birds at the nesting season. 



It sometimes happens that a bird lays an egg and 

 then proceeds to build a nest on top of it. 



Again, some birds do not know their own eggs. 

 A whole clutch of different ones may be substituted for 

 those upon which the bird is sitting and the bird will 

 not discover the change. 



The well-known bird-photographer, Mr. R. Kearton, 

 was desirous of obtaining a good photograph of a 

 sitting thrush, and as he was afraid that her eggs would 

 be hatched before a fine, sunny day presented itself, had 

 some wooden dummies made. These he painted and 



