The Migration of Birds 185 
leave; by July twentieth the bobolinks are collecting 
into small flocks, while a few days later the red-winged 
blackbirds are gathering in considerable numbers 
among the tall reeds along the larger water courses. 
These are the first signs of the fall migration. Dur- 
ing August, bird life, considered as a whole, is at 
low ebb. Some species are slowly collecting, others 
are roving about as families. There is very little 
singing; although the indigo bunting and the red-eyed 
vireo are still tuneful, and occasionally a sparrow is 
heard by the roadside. 
Early in September there is a marked change; the 
warblers are passing in considerable numbers, and 
about the twentieth we are overwhelmed by their 
thousands. We must now begin to look for our 
winter residents, such as the junco and the winter 
wren. The summer residents are fast going, and 
through October and November and into December 
the various sparrows remain, but finally they, too, 
retreat before the increasing cold and snow. 
The manner of migration is a_ study in itself. 
Whether we decide that birds find their way by in- 
stinct or by heredity of habit, we marvel at it none 
the less. It is wonderful that birds can travel such 
great distances over mountain, forest, and plain—and 
even for a considerable distance over the sea—and 
