34 THE MIGRATION OF BIRDS 



extent of a wide river valley, or to a fly-line repre- 

 sented on a map by a ruled line, which passes over 

 certain ascertained places. The absurdity of 

 Gatke's arguments are proved by the study of his 

 truly remarkable book. According to him the 

 island of Heligoland was only remarkable in that 

 it possessed an observer, himself, who saw marvels 

 unobserved elsewhere, though the same number 

 of birds were every year passing over any particular 

 spot in an area which, for many species, must 

 have been many degrees in extent. 



Had not so much weight been placed upon, 

 and so many arguments based on Gatke's extra- 

 ordinary statements by, unfortunately, many of 

 our leading British ornithologists, his theories might 

 have been ignored. Unfortunately he is looked upon 

 as an authority, even an oracle, whereas, as Dr 

 Allen pointed out, on many points which he treats 

 with great positiveness his knowledge is obviously 

 as limited as the little field which was the scene of 

 his life-long labours (2). Glibly he tells of hooded 

 crows " in never-ending swarms of hundreds of 

 thousands " passing across and for many miles on 

 either side of the island ; of " every square foot of 

 the island " teeming with goldcrests, and of " dark 

 autumn nights " when " the sky is often completely 

 obscured" by the migrants, which pass thousands 

 of feet overhead. How did he observe the obscured 



