2 THE SECOND BOOK OF BIRDS 
thology, have placed the birds in groups which 
they call families, to make it easier to find out 
about them, and write about them. This way of 
arranging them in books is called classification 
— or forming them into classes. 
Birds are classified, not by the way they look, 
but by the way they are made, or their structure, 
and this is found out by the study of Scientific 
Ornithology. Birds may look a good deal alike, 
and act alike, and yet be differently made. 
There is first the grand class Aves, which 
includes all creatures who wear feathers. This 
class is divided into orders. 
Orders are made by putting together a large 
number of birds who are alike in one thing. For 
instance, all birds who have feet made to clasp a 
perch, and so are perchers, are put m an order 
together. 
But many birds have feet for perching who 
are very different in other ways. So orders are 
divided into families, which I shall tell you about 
in this book. 
In each family I shall tell you about one or 
more of the best known, or the ones you are most 
likely to see, and that will help you to know the 
rest of the family when you begin to study birds 
out of doors, and use the manual to learn the 
names. , 
