ROUTES OF MIGRATION -33 



tricts will all mark the Route of Migration followed by 

 the several species that reside only in such localities. 

 The migration routes of the Dotterel, for instance, will, 

 broadly speaking, follow the mountain uplands ; and 

 this may explain why so little of this species is seen 

 whilst it is on passage. It is also interesting to remark 

 that this bird is known to pass on migration the districts 

 where it formerly bred. The Ring Ouzel, the Wheatear, 

 and the Merlin will also follow a mountainous route, as 

 the direction along which their past emigrations were 

 carried. The routes of such species as Sandpipers and 

 Ducks will follow rivers and lakes ; those of the Rails 

 and Snipes will follow the northern trend of the swamps ; 

 those of the Stone Curlew and the Nightjar the heath 

 systems and the commons ; whilst those of such species 

 as the Hobby and the Honey Buzzard would be confined 

 to the northern extension of woods. In many cases 

 these Routes have lapsed as Breeding Routes, either 

 through modification of climate, as the northern exten- 

 sion of breeding range spread over our area, or the 

 disappearance of suitable breeding grounds, as such 

 have been " improved " away. Such Routes will con- 

 tinue, however, to be followed by the descendants of 

 birds that increased their range along them. In the 

 utter absence of detailed information, I shall refrain 

 from more closely entering into the subject of Internal 

 Routes ; but I may refer the reader, in addition to the 

 above information, to what I have already said in the 

 Migration of Birds (pp. 242-245). 



