Throughout this period—from July to October—the marsh is used only as a dormitory, the reeds evidently offering suitable perches to these weak-footed birds, who in the morning radiate throughout the surrounding 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 conspicuous. 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 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. [Illustration: 48. “Bird notes”—Tree Swallows.] These evening flights begin about two hours and a half before sunset, when the birds, after resting during the late forenoon and early afternoon, usually on some telegraph wire,^{48} begin to wheel and circle over the fields in pursuit of their evening meal, when one might imagine they were resident birds, but observation will show that the general trend of their movement is toward the roost. This continues for an hour to an hour and a half, a cloudy evening hastening their actions, when their flight becomes more direct. Few birds pause to feed, but hurry on to the roosting places, and as the light fades the last birds rush through the gloom with arrowy speed and directness. The birds pass in straggling flocks, and periods of abundance are succeeded by intervals of scarcity, as though the individuals which had been associated during the day were journeying home together. Thus the Swallow’s evening flight may be observed throughout the region surrounding the marshes; even in New York city they may be seen feeding above the houses, and after sunset flocks of swift-flying birds are often confused by the telegraph wires, which, however, their dexterity of wing permits them to pass without serious harm. In the marshes the first birds are seen about two hours before sunset. Many follow the course of the river, and if one be at its border splash after splash is heard as the birds dip lightly into the water, followed by soft fluffs as arising from the stream they shake their plumage. Soon the air is filled with Swallows, all streaming toward the roost with increasing swiftness. Many birds, however, as though waiting for some tardy comrades, rest by the way, perching on telegraph wires should they cross the marsh, or when these are wanting, on the tips of the reeds. They invariably face the wind, and when it is from the west the last rays of the sun striking their white breasts make them appear like snowy flowers crowning the reeds. Suddenly, with a rush, they whirl onward to the roost.