THE MIGRATIONS OF THE ROOK 271 



parties sometimes consist entirely of old birds, some- 

 times of old and young, and sometimes, so far as he has 

 been able to determine, wholly of young birds. 



In addition numbers are occasionally observed off 

 the mouth of the Thames and the east coast of Kent 

 crossing the Straits of Dover, as if coming from the 

 south-east coast of France. 



Autumn Inimigi'atioufroin North- Western Europe. — 

 The arrivals on our shores from Northern Europe are far 

 from being extensive, which is not surprising, since 

 Professor Collett informs me that the Rook is not an 

 abundant species in Norway : it appears in the Shetlands 

 and at some of the Orkneys (including the far-outlying 

 islet of Sule Skerry) during October and onwards to mid- 

 November, The birds arrive during the night, some- 

 times in fairly large Hocks, and often remain for a short 

 period before proceeding southwards.^ 



On the east coast of the mainland of Great Britain 

 the arrival of these northern immigrants does not seem 

 to have been observed ; but passage movements south- 

 wards, performed during the daytime, are recorded as far 

 south as Flamborough Head. Similar migrations are 

 witnessed on the west coast of Scotland, chiefly at the 

 Hebridean stations. These diurnal migrations are pro- 

 bably passage movements to British winter quarters, 

 and they sometimes extend as far westward as the 

 Flannan and Monach Isles and St Kilda. The Rook 

 is a winter visitor to Barra, and probably to some 

 other of the Hebrides. 



' Mr Thomas Henderson, junior, of Dunrossness, tells me that during 



long-continued southerly gales he has often seen the immigrant Rooks rise 



■ in a flock to a considerable height, as if anxious to be off, and then settle 



down again. They leave Shetland for the south as soon as favourable 



conditions set in. 



