264 THE MIGRATION OF BRITISH BIRDS 



Islands the migration of those species that not only 

 breed in them but pass them is of the longest duration ; 

 the migration of such species that are confined to our 

 islands with no ancient lines of emigration across them 

 is shorter. With the former species individuals con- 

 tinue to pass right through the autumn, the flight 

 beginning and ending in a very gradual manner ; with 

 the latter species, once the movement south commences, 

 it progresses steadily until the end, usually finishing as 

 abruptly as it began. Thus the migration of the 

 Wheatear, a species that has emigrated or extended 

 its range across the British Islands not only to Scan- 

 dinavia, but to Iceland and Greenland, extends over a 

 period of five months, beginning in July, and actually 

 not ceasing before November ! On the other hand, the 

 migration of the Reed Warbler, a species that never 

 emigrated across the British Islands and whose range 

 in them is limited, does not extend over more than a 

 month, beginning say at the middle of August and 

 closing by the middle of September or thereabouts. 

 The migration of the Red-necked Phalaropc is remark- 

 ably contracted both in spring and autumn ; so also is 

 that of the Gargancy. 



Up to the end of September, the general trend of 

 migration across or to the British Islands is from the 

 North or North-cast. After that date a very perceptible 

 change in the general trend takes place, and the pre- 

 dominating line of Flight falls nearl}- to due East. This 

 is the first sign of that gradually approaching wave of 

 migration from the east, from those continental areas 

 which were colonized by birds whose emigrations may 

 be said to have their base in the British Area. Until 

 the middle of September this migration from eastern 



