RECENT EMIGRATION 177 



means. Another very interesting instance of current 

 emigration is furnished by the Rook {Corvus frugilegus). 

 As usual, this Hne of extension is mostly northwards, 

 and has gradually extended until the bird has reached 

 and occupied the Orkneys, and possibly the Shetlands, 

 as a breeding species. A north-western line of Emigra- 

 tion has also been followed, which at present extends 

 as far as Skye, but there seems every possibility of a 

 speedy settlement over the Outer Hebrides. 



The Tawny Owl [Stnx ahicd) within the past half- 

 century has extended its range northwards over the 

 greater part of Scotland — including Skye and some 

 other of the Timer Hebrides — in spite of its decrease in 

 numbers. It still continues, however, significantly absent 

 from Ireland, notwithstanding this emigratory movement 

 elsewhere, and though common enough in the south of 

 Scotland, it never attempts'a southern dispersal in spring 

 to breed in that island. The Ring Dove {Coluinba 

 palumbiis) is another very remarkable instance of cur- 

 rent emigration. Increasing rapidly in numbers, it has 

 initiated a northward extension of area on a very large 

 scale, and within the past century has gradually spread 

 northwards and westwards as a breeding species over 

 Scotland, even to the Hebrides. This species is in its 

 emigrations and migrations analogous to the Greenfinch 

 and the Chaffinch. The Stock Dove {Cohimba cenas) 

 in its recent emigrations presents some very interesting 

 facts which confirm the soundness of our Law of dis- 

 persal in no uncertain way. Twelve years ago the 

 Stock Dove was generally though locally distributed 

 throughout England and Wales, and in the extreme 



north-east of Ireland, where, however, it was said to be 



N 



