180 Biology in America 



included in tlie tropical zone, which except here and at the 

 mouth of the Rio Grande does not enter the United States. 

 In the streams of southern Florida lives the alligator, while 

 the dark forests are the home of the parrakeet, an intruder 

 from the numerous family of parrots in South and Central 

 America. A hundred years ago this bird ranged as far north 

 as the Great Lakes, but it is at present restricted to a few 

 areas in our Southern States, if indeed it is not wholly extinct 

 at present. 



Crossing the Appalachians our traveler descends into the 



The Burrowing O'vvl 



Photo by Eiwin R. Sunburii: 



Courtesy uf the A'e/r York ZoiiJoniiul Hoviity. 



great valley of the IMississippi River, with its branches stretch- 

 ing far to east and west and draining nearly half the total area 

 of the United States. Here he at first encounters a climate 

 not greatly different from that of the eastern seaboard, al- 

 though subject to somewhat greater extremes of temperature. 

 The fauna and the flora too are similar to those of the At- 

 lantic Coast. As he passes westward however out of the basin 

 of the Mississippi, rising over the slope of the Great Plains 

 to the foothills of the Rockies, the climate changes, the rain- 

 fall materially decreasing and the temperature extremes in- 

 creasing. 



Accompanying these changes of climate occur marked 

 changes in the life of the land. The eastern forests disap- 



