166 GRALL^E. 



migration of those dry-land birds which range far in latitude. 

 Cold is the chief cause which drives marsh birds either 

 southward or downward to the warm places. They can find 

 food in all latitudes while the water remains open, and they 

 retire only as these begin to be shut up by the frost. With 

 the forest birds it is different. As the fruit of the deciduous 

 trees ripens, the leaves become dry and unfit for supporting 

 those insects upon which the forest birds live, and thus the 

 birds are driven off even before the severe cold sets in. 



Of those American birds that are confined to the northern 

 division of that continent, we can hardly expect even strag- 

 glers during the northern migration, because the American 

 coast bends so much to the north-east, that a bird from even 

 the Floridas is not likely to make so much leeway as to get 

 eastward to sea. Besides, the wind, especially in the spring 

 and autumn, blows north or south along the central valley of 

 America, and the wind of the eastern shore is influenced 

 northerly by the current of the Gulf-stream, the tendency of 

 which is to keep the northward-bound birds inwards to the 

 land. The set of the winds must indeed influence the south- 

 ward migration of the birds also ; and it is only random 

 stragglers from very northerly places which can at all find 

 their way to Britain.* 



To what extent the intercourse by shipping between coun- 

 tries that lie at a considerable distance from each other, may 

 affect the migration of birds from the one to the other, has 



* According to Bonaparte (" Birds of Europe and North America"), 

 the Botaurus lentiginosus is not the American bittern, which Wilson 

 describes as Ardea minor (Botaurus minor, Bonap.). Bonaparte does 

 not irive the locality of Botaurus lentiginosus, but states that it is "acci- 

 dental in Kurope." It is to the Botaurus minor that the foregoing 

 description refers. If this accidental European bittern and the American 

 species be truly distinct, they are at least very closely related to each 

 other : but in truth, we know not to what species the specimen described 

 by Montagu as Ardca lentiyinosa is referable; it might have been the 

 true American bittern. M. 



