WHERE SWALLOWS ROOST 97 
rounding country and in the evening return to the 
marsh to sleep. In the evening they fly low, and 
the altitude and time of their flight make them con- 
spicuous. In the morning they fly high, as though 
bound to some distant feeding ground, and at so 
early an hour that they usually escape observation. 
The evening flight, therefore, is generally considered 
48. “ Bird notes »— Tree Swallows. 
as truly migratory, when, in fact, the same birds 
doubtless pass over a given locality night after 
night, perhaps for weeks, in returning to their 
roosts in the marshes. 
These evening flights begin about two hours and 
a half before sunset, when the birds, after resting 
during the late forenoon and early afternoon, usu- 
ally on some telegraph wire,** begin to wheel and 
8 
