86 STUDIES IN BIRD-MIGRATION 



their haunts on the opposite side of the North Sea are 

 sealed by ice. 



There are some remarkable features associated with 

 these east to west autumn passages: — (i.) They are 

 frequently observed for several, and sometimes many, 

 consecutive days.^ (2.) They take place chiefly during 

 the daytime. {3.) Not a few, probably most, of these 

 migrants are proceeding to winter quarters in our 

 islands, which are situated in latitudes north of their 

 summer haunts — a most singular circumstance, but one 

 which is to be explained by the remarkably mild 

 temperature of our winters, the winter isotherm for 

 Enofland beingf the same as that for western and 

 southern France. (4.) On some occasions those birds 

 which are proceeding westwards or northwards actually 

 cross the course of the coasting migrants moving south- 

 wards along our eastern sea-board at the same time. 



The return movements in spring towards the east 

 are witnessed, along the same lines of flight, from the 

 middle of February to the middle of April. 



In the autumn of 1903, I spent nearly five weeks in 

 the Kentish Knock light-vessel, which lies 'XtZ miles off 

 the coast of Essex and about the centre of this 

 interesting stream of migration, in order to investigate 

 the various conditions under which these east to west 

 movements were performed, and with a view to ascertain- 

 ing the species participating in them. The results were 

 highly satisfactory, and these, along with my singular 

 experiences, are related in Chapter XVIII. (Vol. 11.). 

 Other information will be found in the studies devoted 

 to migrations performed by the Rook, Starling, and 

 Lapwing. 



' See the history of the migrations performed by the Skylark. 



