THE PHILOSOPHY OF BIRDS’ NESTS. 219 
good, sometimes distinctly, sometimes more obscurely 
apparent, according as the habits of the species are 
more marked, or their structure more peculiar. It 
is true that, among birds differing but little in struc- 
ture or habits, we see considerable diversity in the 
mode of nesting, but we are now so well assured that 
important changes of climate and of surface have oc- 
cured within the period of existing species, that it 
is by no means difficult to see how such differences 
have arisen. Simple habits are known to be here- 
ditary, and as the area now occupied by each species 
is different from that of every other, we may be sure 
that such changes would act differently upon each, and 
would often bring together species which had acquired 
their peculiar habits in distinct regions and under 
different conditions. 
How do Young Birds learn to Build their First Nest? 
But it is objected, birds do not learn to make their 
nest as man does to build, for all birds will make 
exactly the sarne nest as the rest of their species, even if 
they have never seen one, and it is instinct alone that | 
can enable them to do this. No doubt this would be 
instinct if it were true, and I simply ask for proof 
of the fact. This point, although so important to the 
question at issue, is always assumed without proof, and 
even against proof, for what facts there are, are op- 
posed to it. Birds brought up from the egg in cages 
do not make the characteristig ‘nest of their species, 
even though the proper materials are supplied them, 
