132 THE MIGRATION OF BRITISH BIRDS 



passage more prolonged, but the migratory birds with 

 unyielding persistence continued to cross and re-cross it ; 

 until in the course of ages the North Sea occupied the 

 land, and the contour of our islands and the opposite 

 continental coasts gradually became as it exists to-day. 

 Birds continue to migrate in countless hosts across this 

 wide sea-passage, their ancestors having done so in the 

 remote past when dry land replaced the sea ; and no 

 single generation of birds has been able to notice any 

 portion of the vast change which centuries of submer- 

 gence has accomplished. This is a sufficient explanation 

 of the wonderful migration which takes place in spring 

 and still more marked in late autumn across the North 

 Sea to our islands now. The principal species that 

 have emigrated in the past by this route, and which 

 continue to migrate along it in the present, are specified 

 below. 



Species whose lines of Emigration from our 

 area extend East alone. 



Turdus viscivorus. 

 Turdus musicus. 

 Pratinola rul)icoln. 

 Accentor modularis. 

 Parus caTuleus. 

 Parus major. 

 Troglodytes parvulus. 

 Frint;;illa carduelis. 

 Linota caniiabina. 

 Passer niontaiius. 

 Emberiza miliaria. 

 Emberiza citrinella. 

 Emberiza schioniclus. 

 Garruius glandariiis. 

 Corvus corone. 

 Corvus frugilegus. 

 Accipiter nisiis. 

 Otis tarda. 

 Podiceps rubricollis. 

 Botaurus steliaris. 



Species whose lines of Emigration from oi 

 area extend both East and North-East. 



Merula merida. 

 Erithacus rubecula. 

 Regidus cristatus. 

 Eringilia chloris. 

 Eringilla ccvieb.s. 

 Sturnus vulgaris. 

 Corvus monedula. 

 Corvus coriiix. 

 Alauda arveiisis. 

 A-sio brachyotus. 

 Cohimba paUimbui, 

 \'aneiliis cristatus. 

 Crus communi:^. 

 Cygnus olor. 



