10 



are pointed to as evidence of the undeviating character of the 

 latter movement, their appearance on the island being described 

 as of the rarest, though, hke the Siberian examples several have 

 been obtained more than thrice. 



So far, however, from treating the Siberian species as erratics, 

 though their normal line of flight is also admitted to be north to 

 south, they are supposed to be affected by some law or impulse to 

 abandon the route pursued by the vast majority of their fellow- 

 travellers, and to turn to the west by a voluntary act, which is 

 not to be interpreted in the light of an accident, but in another 

 place is explained as due to the prevalence of certain peculiar 

 meteorological conditions at the time of their departure. 



It must not be forgotten, too, that the flight of these Asiatic 

 species, in common with the European, comes equally under the 

 definition of the "broad migratory column" as before described. 

 Many should, therefore, be found passing through or wintering in 

 western and southern Europe in considerable numbers. 



In Herr Gatke's opinion, the lack of evidence that such is the 

 case is due to the fact that certain of them are so inconspicuous 

 in size and appearance that the chances are all in favour of their 

 escaping detection. This, he especially insists upon, is the case 

 with the Yellow-browed "Warbler, which, he thinks undoubtedly 

 occurs in some numbers in Great Britain every year. In cop; 

 sidericg the chances of this contingency he overlooks one fact 

 however. This species has most often been obtained in Heligo- 

 land in the month of October. Now in Great Britain, at this 

 period of the year, all the other Phylloscopi will have already 

 retired to their winter quarters. The appearance of a solitary 

 example, therefore, would be sure to attract the attention of any 

 observer interested in bird-life, and probably lead to the detec- 

 tion of the stranger. The call-note, too, has been described by 

 Seebohm as quite distinct from that of its European congeners. 



The case of Anthus Bichardi is still more striking, though 

 this species has been far more frequently detected in western 

 Europe than the former. But, whereas, if by Gatke's rule the 

 Yellow-browed Warbler should occur in hundreds, Eichard's 

 Pipit should be wintering somewhere in tens of thousands, or as 

 he puts it himself, in incomputable numbers, and that such a 



