4 THE BIRDS OF THE BRITISH ISLES. 



making "records" (a misapplied and evil term) that they hear 

 the Chiffchaff when the Great Tit sings, the Cuckoo when a 

 distant dog barks, and see the Swallow when the Starling 

 hawks for flies, or the Fieldfare when the Mistle-Thrush passes 

 over. Yet apart from these imaginations we are faced with 

 one of two conclusions — either birds are changing their habits 

 or we have failed in the past to make accurate observation. 



Much of this is due to the fact that a large number of the 

 birds we see do not remain with us all summer or winter, but 

 are on passage — that is to say, they are travelling through 

 Britain to or from breeding haunts and winter quarters beyond 

 the limits of our land. The times and seasons of these passage 

 birds do not always agree with those of our more permanent 

 summer or winter visitors, although in many cases the species 

 are the same. Many more northerly breeders come through 

 after our summer residents have begun to nest, and, in some 

 cases, the returning birds pass after ours have departed. 

 Northward migration begins to be visible in February, and lasts 

 until the end of June or even the beginning of July. Southward 

 movements may be noticed before the end of July, and in 

 August many of our birds leave us, but throughout September 

 and October, even until the early days of November, there 

 are birds constantly passing south. In November, December 

 and January we may have extra winter movements, caused by 

 abnormal weather conditions here or abroad. There is 

 practically no season when movement of one kind or another 

 cannot be seen, and now we realise that all those sporadic and 

 local movements, which were formerly looked upon as purely 

 casual, are intimately connected with the migration habit. 



For the study of geographical distribution the world has been 

 divided into zoological regions, now usually accepted as six or 

 seven well-defined areas. The Palaearctic embraces Europe, 

 Africa north of the Sahara and Asia north of the Himalayas. 

 The Nearctic is America north of Mexico, and the two together 



