desired direction and follows only the general trend of the land mass. 

 Oceanic routes appear to be special cases that are not fully 

 understood at the present time. Also it must be remembered that all 

 the main routes contain a multitude of tributary and separate minor 

 routes. In fact, with the entire continent of North America crossed by 

 migratory birds, the different groups or species frequently follow 

 lines that may repeatedly intersect those taken by others of their own 

 kind or by other species. The arterial or trunk routes, therefore, must 

 be considered merely as indicating paths of migration on which the 

 tendency to concentrate is particularly noticeable. 



81 



