THE MIGRA TION OF INLAND BIRDS. 115 



but in the spring, when every bird, if possible, returns 

 to its own home and former nest, they will not linger on 

 the way, as they know too well the length of the journey 

 before them. The coming duties of incubation, too, speed 

 them on, and we wonder why they are not more regu- 

 lar in their movements. In autumn all this is changed. 

 Now nothing need hurry them, and, so long as they find 

 an abundance of food, they move along leisurely, just 

 keeping ahead, as it seems, of the chilling frosts of the 

 coming winter, which they can easily endure, but which 

 robs them of the food they must have. This is espe- 

 cially true of insect-eating birds. Considered in this 

 light, we are not surprised to find, then, as a rule, that 

 the warblers, swallows, and such other birds as depend 

 wholly upon insects for their sustenance, leave more 

 promptly, and in larger numbers at one time, than do 

 the granivorous birds and those that can subsist on seeds, 

 though they consume insects as long as they can find 

 them. 



The weather, both during September and October, is 

 exceedingly variable, although never really wintry, and 

 this fact makes the southward movements of the migra- 

 tory, insect-eating birds equally so, inasmuch as these 

 birds are not larvae-hunting species, but depend upon in- 

 sects that can be caught upon the wing, or are to be 

 found resting upon the leaves and twigs of the trees. 

 Therefore, just so long as the heavy white frosts are de- 

 layed, these insectivorous birds will linger, or move 

 southward in the most leisurely way. Up to a certain 

 time, usually about the middle of October, these birds 

 largely increase in numbers, consequent upon the daily 

 accession of those from the north, and after the maxi- 

 mum is reached, their number steadily decreases, until 

 but a few stragglers remain. 



