MIGRATION ()lv‘ BIRDS. 
     
    
   
   
    
     U! 
     
    
   
   
    
     intensity of color in regions of greatest: rainfall. They are thus evi- 
     
     dent-es of an evolution so recent that we can assign its cause. 
     
    

    
     In nomenclature these partly formed species are tertned subspecies 
     
     0r races. Under the trinomial system they are distinguished by a. 
     
     third name : thus Colours rirginl'tmusflart'tlauus is a sttbspeeiesor 'ace 
     
     of (Juli/m.»- rirgiuz'uuzm. But if through any change in tlte earth’s sur- 
     
     face the regions occupied by the large, light Quail and the small, dark 
     
     otte should be separated, tlte intermediates would disappear and in- 
     
     stead of a race or subspecies we would have a full speeies—C‘o/mus 
     
     flu] iclmuzs. 
     
    

    
     The .lIzZt/I'alion of Is’L'rtIs.—t'ertain insects, fishes, and mammals 
     
     migrate, but no animals compare with birds iii the extent of their 
     
     migrations. Some birds nest within the Aretie Cirele and winter in 
     
     the southern parts of the southern hemisphere. performing,r this jour- 
     
     ney of thousands of miles year after year and returning to their sum- 
     
     mer or winter haunts with marvelous certainty aml regularity. 
     
    

    
     Not only is tlle migration of birds an interesting.r subject in itself. 
     
     but the almost Constant changes it causes in the bird-life of the same 
     
     region gives an interest to the study of ornithology whieh is ever re- 
     
     newed with the changing seasons. Indeed, to the lover of Nature 
     
     birds are a living calendar. "What was that sound that came on the 
     
     softened air ‘2 It was the warble of the l'llnebird from the sC'aggy 
     
     orchard yonder. When this is heard. then has springr arrived.” 
     
    

    
     A discussion of the origin of bird migration will be found in the 
     
     books and papers on this snbjeet to whieh reterenee has been given. 
     
     Here it is possible only to outline its prineipal features as they exist: 
     
     to—day. Generally speaking. birds migrate at the approaeh of winter, 
     
     in search of food. The reason why they leave a land of plenty in the 
     
     tropics and follow the footsteps of retreating winter to nest. in the 
     
     compa 'atirely barren north is as yet not satisfaetorily explained. 
     
    

    
     As a rule. the extent of a bird's migration depends upon the nature 
     
     of its food. Inset-teat ing birds are forced to extend their migrations 
     
     much farther than the seed-eaters. many of \\'l1i('ll are permanent 
     
     residents at their plaee of birth. The land-birds of the Western 
     
     States winter in )lexieo. A few eross the Isthmus of 'l‘elntantepee 
     
     into Central Ameriea. but praetieally no speeies cross the isthmus of 
     
     Panama. Our liastern birds have a longer and more perilous journey 
     
     to perform. 'l‘hey leave the mainland byway of Florida. and some 
     
     speeies find congenial winter haunts in the West Indies or (Tentral 
     
     Atlleriet. while others go as far south as the Argentine Republic. 
     
    

    
     '-it'ds of strong llie‘ht. like Swallows. t-an easily eseape from bird- 
     
     killing Hawks. and so migrate, boldly by day. But the, shy. retiring 
     
     inhabitants of woods and thickets await the coming of darkness, and