BIRDS. 373 



Colymhus {Eudytes) are peculiar to the cold regions of tlie northern 

 hemisphere; in the seas of the southern hemisphere, the species of 

 the genus Aptenodytes, are met with as their representatives. In cold 

 countries few land-birds, that feed on vegetable food, are found; they 

 belong to the genera Emheriza, Fringilla, Tetrao. Towards the tem- 

 perate regions of the northern hemisphere, with the number of vege- 

 table species, the number also of birds, that derive their food from 

 the vegetable kingdom, increases. The number as well of species as 

 of genera of land-birds that never occur in high northern latitudes 

 increases more and more. The temperate zones of the northern 

 hemisphere have in all countries a correspondence greater in pro- 

 portion to tlieir proximity to the polar zone, so that in high lati- 

 tudes different Asiatic and European species occur also in America. 

 This is, however, the case with the swimming-birds especially. 

 Thus, for instance, Mergus alhellus, Mergus serrator, many species 

 of ducks, Anas boschas, Atias clypeata, occur equally in North 

 America and in Europe. Amongst the fen-birds also there is a 

 certain uniformity, especially in some species of Tringa, and to 

 a certain extent amongst the birds of prey ; but amongst the sing- 

 ing birds the uniformity in the temperate regions disappears almost 

 entirely, or is limited to some similar species, which former writers, 

 less acquainted with the accurate discrimination of species, regarded 

 as identical. The greater the proximity to the tropic the greater also 

 is^the difference of species. Here also the American genera differ 

 more and more from those of the old world. In tropical regions 

 the species of the temperate zone almost entirely disappear, but are 

 often represented, however, by other species of the same genera. 

 Under the tropics, as it appears, alP the species of American birds 

 differ from those of the old world. Species of birds, which in the 

 proper sense are dispersed over the whole world {species cosmopolitce) , 

 do not exist, although there are species which are spread over the 

 northern hemisphere from the high north to the north coast of 

 Africa and eastwards over many countries of Asia; such are 

 Charadrius pluvialis, Strepsilas collaris, and some others. Large 

 genera, dispersed almost everywhere, are Falco, Strix, Turdiis, 

 Corvus, Sturnus, Fringilla, Emheriza, Ptcus, Coltimha, Charadrius, 



^ Or almost all; an exception is formed by Anas viduata L. from South America 

 and the west coast of Africa. 



