394 GENERAL ZOOLOGY 



America. Its habits, song, and call notes offer an interesting 

 subject for study. 



Migration of Birds. The phenomena of migration are es- 

 pecially noteworthy among birds, and the birds of a region 

 may be roughly classified in connection with this habit. 

 Those species which remain in a region all the year are 

 spoken of as permanent residents of that region. They may 

 be more or less migratory as individuals ; that is, the birds 

 seen in the summer may not be the same individuals that 

 appear in the autumn or winter. The great majority of the 

 birds of the northern hemisphere leave in the autumn to 

 pass the winter in the south, returning in great bird waves 

 in the spring. These birds are the summer residents of the 

 region. The summer residents of the eastern United States 

 may pass the winter in the Southern states, or they may (like 

 the bobolink) go as far as Brazil (Fig. 209). When the great 

 hordes of the summer residents have passed to the south, 

 other birds come down from the north ; these are winter visi- 

 tants. Often a bird loses its way, or is blown out of its regu- 

 lar line of travel to other regions ; such birds are accidental 

 visitants to those regions. 



The great migratory movements of birds are fairly regular 

 year after year, and they are participated in by thousands 

 upon thousands of individuals. When the appropriate time 

 comes each species gathers in large flocks, or the individuals 

 separately move off on their long trip. The larger birds, with 

 special means of defense, as the large hawks and cranes, 

 choose daylight in which to travel. Ducks and geese mi- 

 grate in flocks, flying either by day or by night. Some of 

 the smaller birds which are also rapid and untiring fliers, 

 like the swallows, also carry on their migrations during the 

 day, but most of the smaller birds migrate at night. A foggy 

 night causes the death of large numbers of birds ; over fif- 

 teen hundred individuals have been picked up at the foot 



