DO ANIMALS THINK AND REFLECT? 
above described. All yellow warblers act in the same 
manner, which is the way of instinct. Now if this 
procedure was the result of an individual thought 
or calculation on the part of the birds, they would 
not all do the same thing ; different lines of conduct 
would be hit upon. How much simpler and easier 
it would be to throw the egg out — how much more 
like an act of rational intelligence. So far as I know, 
no bird does eject this parasitical egg, and no other 
bird besides the yellow warbler gets rid of it in 
the way I have described. I have found a deserted 
phcebe’s nest with one egg of the phoebe and one of 
the cowbird in it. 
Some of our wild birds have changed their habits 
of nesting, coming from the woods and the rocks to 
the protection of our buildings. The phcebe-bird 
and the cliff swallow are marked examples. We 
ascribe the change to the birds’ intelligence, but to 
my mind it shows only their natural adaptiveness. 
Take the cliff swallow, for instance; it has largely 
left the cliffs for the eaves of our buildings. How nat- 
urally and instinctively this change has come about! 
In an open farming country insect life is much more 
varied and abundant than in a wild, unsettled coun- 
try. This greater food supply naturally attracts the 
swallows. ‘Then the protecting eaves of the buildings 
would stimulate their nesting-instincts. The abun- 
dance of mud along the highways and about the 
farm would also no doubt have its effect, and the 
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