54 MANNER OF MIGRATION. 



4. Transient Visitants. — -Birds whose summer home 

 is north and whose winter home is south of us. In 

 travehng from one to the other they pass through the 

 intervening region as " transients." 



Manner of Migration. — The 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- 



