16 INTRODUCTION. 



were not so sharp-sighted as the ornithologists of to- 

 day. It is not within the scope of this volume to 

 enter into the varied details of the migration of our 

 birds. It is a moderately uniform movement from 

 points widely distant, and the question of a food- 

 supply is the principal incentive. When migration 

 commenced, and why, cannot be determined. Geo- 

 logically, probably, it is of recent date, that is, 

 brought about by changes wrought during the 

 growth, climax, and disappearance of the Glacial 

 Period; but of course all this is conjectural. We 

 cannot conceive of migration in a climate without 

 seasonable changes, unless an effort to escape enemies 

 during the breeding period should induce a general 

 exodus from the ordinary haunts ; but these enemies 

 would soon be able to follow unless a climatic bar 

 shut them out. Coming down to details in the mat- 

 ter, and considering individual species rather than 

 birds en masse, it will be found that many birds that 

 migrate in easy stages are very deliberate, and when 

 they find comfortable quarters remain until a change 

 of weather warns them to proceed. This is not 

 noticeable to any degree in the spring-tide northward 

 journey, but is very decided in the autumn return 

 trip along the Atlantic coast, and presumably equally 

 true of the interior. Early or late in September, as 

 the case may be, the woods will fill up with warblers. 

 Even the trees along the village street and the bushes 

 in town gardens will be visited by a throng of dainty 

 birds, some conspicuously colored, but mostly plain 

 and likely to pass unnoticed, unless their ceaseless 

 activity calls attention to them. Often they do not 



