72 THE BIRD GROWN UP 
would think they needed to have numbers on 
their doors, to know which was their own. 
There, too, are the common crow blackbirds. 
They come in the spring in crowds, and when it 
is time to make nests, they find some grove or 
clump of trees that suits them, and all of them 
build their nests close together. Often there are 
two or three on one tree, like a bird city. There 
they live and rear their little ones, and it is said 
they never quarrel. 
Then there are the birds who get their food 
from the sea, such as penguins. These birds live 
in big cities, of many thousand nests. They go 
to an island where no people live, and build on 
the ground, or on rocks, or anywhere. 
Sometimes they are so near together one can 
hardly walk without stepping on them. How 
each mother can tell her own, it is hard to see. 
They live very happily together, and if a mother 
is killed, so that her little ones are left orphans, 
one of the neighbors will adopt them all, and 
feed and bring them up with her own. 
Some of these birds do not even take the 
trouble to make a nest. They put the eggs any- 
where on the sand or earth. 
Some one, Mr. Brehm, I think, tells a pretty 
story about a certain kind of duck who rears two 
broods every season. After the ducklings of the 
