54 MANNER OF MIGRATION, 
4. Transient Visitants——Birds whose summer home 
is north and whose winter home is south of us. In 
traveling from one to the other they pass through the — 
intervening region as “ transients.” 
Manner cf Migration—tThe Oriole, who builds his 
swinging nest in your elm tree, will winter in Central 
America; the Bobolink, who seems so care-free in your 
meadows, must journey to his winter quarters in southern 
Brazil. But, unless accident befalls, both birds will re- 
turn to you the following spring. We are so accustomed 
to these phenomena that we accept them as part of the 
changing seasons without realizing how wonderful they 
are. But look for a moment at a map, and try to form 
a mental picture of the Bobolink’s route. Over valleys, 
mountains, marshes, plains, and forests, over straits and 
seas hundreds of miles in width, he pursues a course 
through trackless space with a regularity and certainty 
which brings him to the same place at nearly the same 
time year after year. How much of his knowledge of 
the route he has inherited, and how much learned dur- 
ing his own lifetime, is a question we may return to 
later; now we are concerned with actual methods of 
migration. 
Immediately after, or even during the nesting season, 
many birds begin to resort nightly to roosts frequented 
sometimes by immense numbers of their kinds, with 
often the addition of other species. These movements 
are apparently inaugurated by the old birds, and are in 
a sense the beginnings of the real migratory journey. 
Other birds roam the woods in loose bands or families, 
their wanderings being largely controlled by the supply 
of food. 
During this time they may be molting, but when 
their new plumage is acquired they are ready for the 
start. The old birds lead the way, either alone or asso- 
