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quarters southward, cannot be doubted. But how can 

 we account for the fact that large numbers of young 

 birds yearly commence their southerly migration in 

 July, and that some species, the Swift for example, 

 leave our shores to a bird early in August, when tem- 

 perature and food supply are alike at their highest 

 point. 



Then, again, why do birds return every spring 

 rom their winter haunts in tropical and subtropical 

 regions, to their less plentifully-endowed northern 

 breeding areas ? A natural longing to nest year after 

 year, not only in the same district, but also in the 

 identical spot, is widely apparent ; but whence comes 

 it? 



The subject of exceptional migration can only be 

 briefly referred to here, and in conclusion. The 

 advent of rare and unusual bird visitors seems to be 

 partly due to exceptional meteorological conditions. 

 This seems to be the cause of the occasional appear- 

 ance in Britain of the Crossbill and Waxwing, and of 

 the invasions of Pallas' Sandgrouse, an Asiatic species 

 which visited our shores in 1863 in considerable, and 

 in 1888 in enormous, numbers. 



But the majority of rare occurences seem to 

 depend on fixed laws. Many species which have 

 their normal migration routes in Eastern and Central 

 Asia, for instance, seem to be influenced in such away 

 that numbers of individuals are periodically deflected 

 from their course in a westerly direction, and appear 

 as rare stragglers in Western Kurope. 



