DIFFICULTIES OF THE THEORY 247 



pecker for climbing trees and seizing insects in the 

 chinks of the bark? Yet in North America there are 

 woodpeckers which feed largely on fruit, and others with 

 elongated wings which chase insects on the wing. On 

 the plains of La Plata, where hardly a tree grows, there 

 is a woodpecker (Colaptes campestris) which has two toes 

 before and two behind, a long pointed tongue, pointed 

 tail-feathers, sufficiently stiff to support the bird in a 

 vertical position on a post, but not so stiff as in the 

 typical woodpeckers, and a straight strong beak. The 

 beak, however, is not so straight or so strong as in 

 the typical woodpeckers, but it is strong enough to bore 

 into wood. Hence this Colaptes in all the essential parts 

 of its structure is a woodpecker. Even in such trifling 

 characters as the coloring, the harsh tone of the voice, 

 and undulatory flight, its close blood-relationship to our 

 common woodpecker is plainly declared; yet, as I can 

 assert, not only from my own observations, but from 

 those of the accurate Azara, in certain large districts it 

 does not climb trees, and it makes its nest in holes 

 in banks! In certain other districts, however, this same 

 woodpecker, as Mr. Hudson states, frequents trees, and 

 bores holes in the trunk for its nest. I may mention as 

 another illustration of the varied habits of this genus, 

 that a Mexican Colaptes has been described by De Saus- 

 sure as boring holes into hard wood in order to lay up 

 a store of acorns. 



Petrels are the most aerial and oceanic of birds, but 

 in the quiet sounds of Tierra del Fuego, the Puffinuria 

 berardi, in its general habits, in its astonishing power of 

 diving, in its manner of swimming and of flying when 

 made to take flight, would be mistaken by any one for 



