RECENT EMIGRATION 175 



area in question has still been crossed on passage by 

 birds that have continued to breed in Scandinavia) ; 

 but which, as we have seen, there is now absolute 

 proof that it is slowly expanding north again with 

 the return of more favourable conditions. This exten- 

 sion of area, it should be remarked, is being carried 

 out by individuals that breed in Scotland, and is quite 

 independent of the migratory individuals that cross it 

 on passage to Scandinavia. The increase of the Starling 

 in Scotland presents very similar facts. 



The extension of range of the House Sparrow {Passer 

 dojiiestiais) has so very much depended upon the spread 

 of cultivation and the reclamation of waste grounds, 

 that it is almost impossible to separate the thoroughly 

 normal increase of area of this species from that which 

 has solely depended upon artificial aid. However, the 

 species is one that is unquestionably extending its area 

 of distribution, due in a great measure to its abnormal 

 increase in numbers (owing to the extermination of 

 many of its enemies and its artificial conditions of 

 existence), and is now common and well established in 

 many northern areas, where within the range of historic 

 time it was absolutely unknown. The Tree Sparrow 

 {Passer montanus) is also extending its range north- 

 wards, and apparently increasing in numbers ; but it is 

 most significant that this fact does not apply to the 

 south-west of England — a direction of extension which 

 would involve a southern emigratory movement. A few 

 pairs of this Sparrow reached the Faroes some twenty- 

 five years ago, and have multiplied to such an extent as 

 literally to become a pest ! The Chaffinch {Fringilla 

 caiebs), again, is increasing and spreading northwards in 



