310 Evolution and Adaptation 



It is even more apparent in species inhabiting open plains. 

 The ears of the gray rabbit of the plains of western Arizona 

 are twice the size of those of the Eastern states. 



In birds the bill especially, but also the claws and tail, 

 is larger in the south. In passing from New England 

 southward to Florida the bill in slender-billed forms be- 

 comes larger, longer, more attenuated, and more decurved ; 

 while in short-billed forms the southern individuals have 

 thicker and larger bills, although the birds themselves are 

 smaller. 



The remarkable changes and gradations of color in birds 

 in different parts of North America are very instructive, and 

 the important results obtained by American ornithologists 

 form an interesting chapter in zoology. The evidence would 

 convince the most sceptical of the difficulty of distinguishing 

 between Linnaean species. It is not surprising to find in this 

 connection a leading ornithologist exclaiming, " if there really 

 are such things as species." The differences here noted are 

 mainly from east to west. We may briefly review here a 

 few striking cases selected from Coues's " Key to North 

 American Birds." 



The flicker, or golden-winged woodpecker {Colaptcs aura- 

 tus), has a wide distribution in eastern North America. It 

 is replaced in western North America (from the Rocky 

 Mountains to the Pacific) by C. mexicanus. In the inter- 

 mediate regions, Missouri and the Rocky Mountain region, 

 the characters of the two are blended in every conceivable 

 degree in different specimens. " Perhaps it is a hybrid, and 

 perhaps it is a transitional form, and doubtless there are no 

 such things as species in Nature. ... In the west you will 

 find specimens auratus on one side of the body, mexicanus 

 on the other." There is a third form, C. chrysoides, with 

 the wings and tail as in auratus, and the head as in mexi- 

 canus, that lives in the valley of the Colorado River, Lower 

 California, and southward. 



