126 THE MIGRATION OF BRITISH BIRDS 



Sweden. These arc the Twite, the Pied Wagtail, and 

 the Rock Dove. We also find that the emigrations of 

 twelve species have only extended as far north as Den- 

 mark ; whilst five have only reached the southern shores 

 of the Baltic. Of these latter, however, it is interesting 

 to note that no less than four are represented in the 

 more northern latitudes by closely allied forms from 

 which it is very doubtful whether they are specifically 

 distinct, except in one instance. These are the Night- 

 ingale, represented in Scandinavia and Denmark by 

 EritJiaciis pJiiloviela, the Dipper in Scandinavia by Cinchis 

 melanogaster, the Bullfinch in Scandinavia by PyrrJuila 

 major, and the Carrion Crow by Corvtis comix. Two of 

 these birds are practically sedentary, their migrations, if 

 any, being limited ; the Nightingale is a migrant, but its 

 line of passage is south-east, which almost completely 

 isolates it from the western race E. liLscinia. Of the 

 twelve species that only reach Denmark, one is repre- 

 sented further north by a local race, viz. the Nuthatch, 

 whose Scandinavian allied form is Sitta europcea. Again, 

 but ten species have extended their emigrations across 

 the British Area to a higher limit than they have done in 

 West Continental Europe. They are the Nightingale, 

 the Gray Wagtail, the Lesser Rcdpole, the Chough, the 

 Carrion Crow, the Lesser Tern, the Great Skua, and the 

 three species of Petrels — all, save one (the Carrion Crow), 

 it may be remarked, thoroughly western types. On the 

 other hand, no less than 74 species range lower in our 

 area than in West Continental Europe. It is to my 

 mind an astonishing fact of distribution — taking into 

 consideration the mild climatal conditions of our isolated 

 area, encircled as it is by the warm waters of the Gulf 

 Stream — that so vast a percentage of species should 



