130 STUDIES IN BIRD-MIGRATION 



obtained on migration at Fair Isle belong to both forms 

 which seek the North for their summer haunts. Thus 

 we have both Phylloscopus trochilus eversmanni and 

 typical T. trochilus as visitors ; the former being the 

 North-Eastern European and Siberian race, and the 

 latter the Scandinavian. 



This bird is one of the most abundant of the smaller 

 migrants visiting the island on its spring and autumn 

 passages. 



In spring it arrives from the south at dates between 

 8th April and 6th June, but is most frequent throughout 

 May, and occurs in rushes down to the end of the third 

 week of that month. Vast numbers appeared between 

 Wth and 15th May 191 1, and all, with one or two 

 exceptions, belonged to the race eversmanni. 



Its autumn movements also cover a considerable 

 period, since they have been chronicled between 7th 

 August and 25th October, the main passages covering 

 the entire month of September. In the autumn of 1910, 

 an early season, it was numerous during the last week of 

 August, and less abundant than usual in September. 

 A few occur annually in October, chiefly during the first 

 half of the month. 



During its visits it is to be found almost everywhere. 

 In spring it is one of the few sylvan migrants that are 

 sufficiently cheerful to indulge in a few notes of song ; 

 and in the autumn I have frequently heard it utter its 

 pretty, plaintive call-note. 



Phylloscopus borealis, Northern Willow- Warbler. 

 — When searching for migratory birds on the 28th 

 September 1908, I disturbed, in a patch of potatoes 

 where it was hiding, a Willow- Warbler with very dark 

 upper plumage. This I was fortunate enough to secure, 



