THEIR PLACE IN NATURE 5 



the land surfaces of the earth. There exists 

 scarcely a single sea-swept rock, sand spit, -or coral 

 key which is not the home of some form of feath- 

 ered life. The north and south polar regions, 

 during their respective summer seasons, are over- 

 run with countless hordes of geese and penguins. 

 The mountain tops have special species of their 

 own. The Sahara Desert is populated with a few 

 small birds and a multitude of vultures. Even 

 the oceans boast of a winged fauna of albatrosses, 

 phalaropes, gulls, and petrels. 



Not only have birds world-wide distribution, 

 but their species are the most numerous of all ver- 

 tebrated animals. Insects and mollusks, alone of 

 all the animal kingdom, surpass them in this re- 

 spect. To-day there are known to exist about 

 19,000 species and subspecies of birds, and numer- 

 ous newly described forms are annually being 

 added to the list. Against these may be named 

 in the scientific calendar something more than 

 15,000 species of fish, about 1000 of amphibians, 

 roughly 3500 of reptiles, and of mammals, the 

 class which we commonly associate with the 

 greatest number of forms of all, only 4500 ! 



Of the now existing continents, South America, 

 with its gigantic rain forest, contains the most 

 varied bird fauna. Upward of 5000 racial forms 

 have thus far been described from there, and prob- 

 ably when the entire region has been exploited 



