In Greensboro, North Carolina, there is a small grove of trees clustered about the courthouse which is a very busy place during the nights of summer. Here, before the first of July, Purple Martins begin to collect of an evening. In companies of hundreds and thousands, they whirl about over the tops of the houses, alight in the trees, and then almost {67} immediately dash upward and away again. Not till dark do they finally settle to roost. Until late at night a great chorus of voices may be heard among the branches. The multitude increases daily for six or eight weeks, additions, in the form of new family groups, constantly augmenting their numbers. Some time in September the migration call reaches the Martins, and, yielding to its spell, they at once depart toward their winter home in tropical South America. _The Usual Movement._--Many of our smaller birds, such as Warblers and Vireos, do not possess a strong flocking instinct, but, nevertheless, they may be seen associated in numbers during the season of the northern and southern movements. Such birds migrate chiefly at night and have been observed through telescopes at high altitudes. Such observations are made by pointing the telescope at the disk of the full moon on clear nights. On cloudy or foggy nights the birds fly lower, as may be known by the clearer sounds of their calls as they pass over; at times one may even hear the flutter of their wings. There is a {68} good reason for their travelling at this time, as they need the daylight for gathering food. There appear to be certain popular pathways of migration along which many, though by no means all, of the aerial voyageurs wing their way. As to the distribution of these avian highways, we know at least that the coastlines of the continents are favourite routes. Longfellow, in the valley of the Charles, lived beneath one of these arteries of migration, and on still autumn nights often listened to the voices of the migrating hosts, "falling dreamily through the sky."