PICARIAN BIRDS. 95 



saucer made of bark and feathers gummed by saliva to a branch, and 

 is so small that the sitting bird entirely conceals it. Only one egg 

 is laid. 



Family XIII. Trochilidj':. Humming-bikds. 



The Humming-birds or Hummers, so called from the sound often pro- [Case t52.] 

 duced by their vibrating wings, are exclusively a New World Group, and 

 must not be confounded with the Passerine group of Sunbirds {Nec- 

 tariniidai), which inhabit the Indian and African regions, and somewhat 

 resemble them in outward appearance and habits. About five hundred 

 species are known ; and of these the majority inhabit Central and South 

 America, but some are found in the southern United States, and 

 Selasphorus rufus (1318) migrates northwards in summer to Canada 

 and even Alaska. Eustephanus galeritus (1273 a) frequents Tierra del 

 Fuego even in snowy weather ; while Oreotrochilus chirnborazo (1304) 

 and 0. pichincha (1303) are natives of the Andes of Ecuador, close to 

 perpetual snow, at a height of 16,000 feet. All are very small birds, 

 the largest being the Giant Humming-bird [Patagona gigas) (1308), 

 about 9^ inches long; while the smallest forms, such as Mellisuga 

 minima (1326) and Chcetocercus bombus (1326 a) are little larger than a 

 bumble-bee and only measure 2^ inches in length. 



The tongue of these birds is very peculiar, being slender, very long, 

 and extensile. When drawn within the bill, the two branches of the 

 hyoid bone which support its base curve upwards around the back of 

 the skull, and then forward over the top of the head, as in the Wood- 

 peckers (see preparation in Case). This arrangement allows the tongue 

 to be suddenly protruded to a considerable distance and as quickly with- 

 drawn. Unlike that of the Woodpeckers, the tongue is hollow and 

 divided at the free end into two slender branches, each of which bears 

 a thin membranous fringe on its outer margin. 



The plumage is usually of a brilliantly metallic nature, produced by 

 the prismatic surfaces of the feathers, and in many forms crests, ear- 

 tufts, neck-frills, and other ornamental plumes add to the gorgeous 

 effect. 



The wing-muscles are greatly developed, and enable the birds to 

 sustain their untiring flight, which is more like that of a hawk-moth 

 than a bird. The little creatures hover in front of a flower, suspended 

 as it were in the air, their wings vibrating so rapidly that they merely 

 appear like a grey film ; an instant they remain poised, and then, with a 

 flash of metallic colour, vanish with incredible speed. 



The length and shape of the bill varies greatly in the different genera ; 

 some have the edges of the mandible strongly serrated towards the tip, 

 while in others this serration is faint or absent. In the absence of 



