138 TROPICAL NATURE, AND OTHER ESSAYS. 



lichen, the body of the nest being formed of cottony 

 substances and the inside lined with the finest and most 

 silky fibres. Others suspend their nests to creepers 

 hanging over water, or even over the sea ; and the 

 Pichincha humming-bird once attached its nest to a 

 straw-rope hanging from the roof of a shed. Others 

 again build nests of a hammock-form attached to the 

 face of rocks by spiders' web ; while the little forest- 

 haunting species fasten their nests to the points or to 

 the under-sides of palm-leaves or other suitable foliage. 

 They lay only one or two white eggs. 



Geographical Distribution and Variation. Most 

 persons know that humming-birds are found only in 

 America ; but it is not so generally known that they are 

 almost exclusively tropical birds, and that the few species 

 that are found in the temperate (northern and southern) 

 parts of the continent are migrants, which retire in the 

 winter to the warmer lands near or within the tropics. 

 In the extreme north of America two species are regular 

 summer visitants, one on the east and the other on the 

 west of the Rocky Mountains. On the east the common 

 N. American or Ruby-throated humming-bird extends 

 through the United States and Canada, and as far as 57 

 north latitude, or considerably north of Lake Winnipeg ; 

 while the milder climate of the west coast allows the 

 Rufous Flame-bearer to extend its range to beyond Sitka 

 to the parallel of 61. Here they spend the whole 

 summer, and breed, being found on the Columbia River 

 in the latter end of April, but retire to Mexico in the 

 winter. Supposing that those which go furthest north 

 do not return further south than the borders of the 

 tropics, these little birds must make a journey of full 



