MH.KATIoN .!- IUIJIS. 5 



intensity of color in regions of rcatct rainfall. They an- thus eri- 

 deuces of an evolution so wont t hat we can assign its cause. 



In nomenclature the-e partly formed species are termed Mil|x-cirs 

 or races. Under the trinomial system they are distinguished by a 

 third name : thus Colinus virginiantu floridnnut is a Mihspecies or race 

 of Colin it* virgin tan u*. Hut if thmugh any change in tin- earth's sur- 

 face the regions occupied by the largo, light (juail and the small, dark 

 one should be separated, the intermediates v.-ould disappear and in- 

 stead of a race or subspecies we would have a full species Colt nun 

 floridanu*. 



The Migration of Birds. Certain insects, fishes, and mammals 

 migrate, but no animals compare with birds in the extent <>f tli.-ir 

 migrations. Some birds nest within the Arctic Circle and winter in 

 the southern parts of the southern hemisphere, performing thi- jour- 

 ney of thousands of miles year after year and returning to ih.-ir sum 

 mer or winter haunts with marvelous certainty and regularity. 



nly is the migration of l.inls an interesting 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 which 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 airt It was the warble of the Bluebird from the scraggy 

 orchard yonder. When this is heard, then lias spring arrived." 



A discussion of the origin of bird migration will be found in the 

 books and papers on this subject to which reference has been given. 



;t is possible only to outline its principal feature- a- Mi- 

 to-day. Generally speaking, birds migrate at the approach of winter, 

 h of food. The reason why they leave a land of plenty in the 

 tropic* and follow the footsteps of retreating winter to nest in the 

 comparatively barren north is as yet not satisfactorily explained. 



As a rule, the extent of a bird's migration de|x>iuU ii|>on the nature 

 >f it- food. Insect-eating liird- are forced to extend their migrations 

 much farther than it '-r-. many of which are permanent 



residents at their place of birth. The land-birds of the \\ 



winter in M A fow cross the Isthmus of Tehuantcpcr 



into Central America, but practically no species cross the Isthmus of 

 Panama. Our Kastern birds have a longer and more perilous journey 

 to jK-rform. They leave the mainland by way of Florida, and some 

 find congenial winter haunts in tin- We-t Indies or Central 

 Arneriea. while others go as far south as the Argentine Republic. 



Hirds nf-troiii: flight, like Swallows, can easily escape from bird- 

 killing Hawks, and so migrate boldly by day. Hut the shy. retiring 

 inhabitants of woods and thickets await the coming of dark new, and 



