SPRING MIGRATIOX IN BRITISH AREA 251 



duties of reproduction. It is noteworthy that all these 

 late coasting individuals not only breed in the high 

 north, but have extended their emigrations across our 

 area thereto, as has been already shown {conf. table, 

 p. 116). 



The spring migration of birds to the British Islands 

 is just as gradual as in other localities situated in 

 temperate latitudes. Birds are almost invariably seen 

 first in the more southern districts ; in cases where this 

 is not so they must have been overlooked. Nearly if 

 not quite two months elapse before the remote northern 

 and western areas are reached. Thus most of the 

 summer migrants to Ireland reach that country a week 

 or even a fortnight later than they appear in the south 

 of England. In the north of England most migrants 

 are at least a week later to arrive than they are in the 

 south, and this is much more marked in some species 

 than others. The Chiffchaff, for instance, must migrate 

 very rapidly across our area, as it is generally seen as 

 soon in the north of England as in the south, at most 

 but a day or so intervenes. On the other hand, the 

 Redstart, the Ring Ouzel, and the Corn Crake must 

 travel slower, for often ten days or a fortnight will 

 mark the difference in the date of their arrival. A still 

 cfreater difference in the date of arrival is almost invari- 

 ably remarked in Scotland. As a general rule the state 

 of the season governs the progress of the migration. 

 If the weather be mild and open birds reach their 

 northern destinations quicker than if the season be a 

 cold, stormy, or backward one. 



The Spring Migration of Birds to the British Islands 

 extends over a period of quite four months. It begins 



