292 THE MIGRATIOX OF BRITISH BIRDS 



upon the Autumn Migration of birds, we trace the first 

 signs of the movement by migrants entering our area 

 from the highest and coldest latitudes as early as July. 

 As the autumn advances the migration gains in strength, 

 and our own summer birds begin to take their departure, 

 that event being more or less directly preceded by the 

 annual moult, and in many cases by the suggestive 

 gathering together of individuals. The vast amount of 

 coasting migration is described, as is also the order of 

 passage and the duration of flight. In the late autumn 

 a very noticeable change in the direction of migration is 

 apparent, and we then proceed to deal with the vast 

 east to west movement across the North Sea. Various 

 apparent anomalies of Flight are then discussed, as are 

 also the presumed change of route and the autumnal 

 descent of migrants from their mountain breeding places. 

 The subject will be too fresh in the reader's mind to 

 require recapitulation in further detail. 



A short chapter dealing with the various Internal 

 Migrations and Local Movements of birds in the 

 British Islands introduces us to a ver}- important branch 

 of the subject, which unfortunately cannot be treated in 

 a very detailed manner owing to the utter lack of neces- 

 sary information. We have shown, however, that all this 

 Internal Migration is purely of a local character, abso- 

 lutely confined to the areas occupied normally by species 

 undertaking it, and therefore controlled by that Law of 

 Dispersal which forbids extension of range during the 

 season of non-reproduction. We next proceed to discuss 

 the effects of abnormally severe winters on birds, and 

 the impotency of such effects to increase or to transpose 

 geographical area ; bringing the subject to a close with a 



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