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 Linnzean 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 (Colaptes 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 avratus 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 mext- 
canus, that lives in the valley of the Colorado River, Lower 
California, and southward. ° 
