12 



doubtful if any species of bird exists in numbers approaching a 

 billion. It is perhaps liardly necessary to point out that for one 

 billion of Hooded Crows to cross a given longitude in the sixty 

 days which Herr Gatke assigns as the duration of the migratory 

 flight of this species, it would be necessary for no less than six- 

 teen thousand six hundred millions to pass each day. It will 

 also be observed that Herr Gatke is not even content with the 

 singular number. Whatever the breadth of the migration column 

 may be, such myriads are inconceivable. 



In the article on "The Guillemot" also, we have another 

 instance in which he allows his enthusiasm to run away with 

 him. Eeferring to this species on p. 578 he writes of " countless 

 myriads of birds swarming about in all directions in the air ; 

 equally innumerable long-extending companies are seen swimming 

 near and far upon the sea " — an artistic description truly, but 

 on further reference to the text we find that these " countless 

 myriads" and " innumerable companies" resolve themselves into 

 some fraction of a breeding colony of only 2,000 birds. 



These remarks are not intended in any hypercritical spirit, 

 but merely to serve as a warning to the reader not to attach 

 too great an importance to statements that such and such species 

 pass Heligoland in numbers which can only be derived from a 

 breeding-range extending throughout the whole of Eastern 

 Europe and Asia. 



In presenting evidence of his theory of an east - to - west 

 migration, Herr Gatke has wisely called attention to the flight 

 of several species which are either conspicuous from their 

 abundance, or from special interest attaching to their history. 

 It will, therefore, be convenient to follow him in his remarks 

 on each of these species in turn. 



Before doing so, however, it may be as well to ascertain what 

 portions of the continents of Europe and Asia we are fairly entitled 

 to consider as belonging to the east. Of course, if we are to include 

 all the vast territory lying to the east of the longitude of Heligo- 

 land, from the Mediterranean in the south to the Arctic Ocean in 

 the north, and in like manner throughout Asia, then the theory 

 of an east-to-west flight may be very easily accepted. But if, 

 on the other hand, and bearing in mind the author's definition 



