XIV 



MIC, RAT I ON 359 



they fly with a tail wind. And a saving of time is 

 a saving of effort. The best evidence in favour of the 

 beam-wind theory is of the kind given by Ilcrr 

 Gatke, who says that he has seen birds heading, not 

 towards their destination, but in a different direction. 1 

 But how is it possible to know exactly for what point 

 they wish to steer ? And how can we penetrate to their 

 motives ? Birds have been seen zigzagging as they 

 flew down an estuary, and this, it is said, had for its 

 object the avoidance of a tail wind. Before such 

 evidence can be accepted, we want careful observations 

 as to the direction of the wind, and then we must 

 consider whether there is not some other perfectly 

 simple explanation of their zigzag course. As a rule 

 it seems that weather does not greatly affect migration. 

 A great storm will, no doubt, sometimes prevent the 

 progress of birds altogether. But the Puffin arrives 

 here punctual almost to the day, and many other birds 

 vary but little in the time of their coming, so that it is 

 clear that they do not wait for some particular wind. 



Wings shaped for Long Flight— From far South to 

 far North. 



Migrants whose two homes are widely separated have 

 wings long and pointed as the necessary equipment 

 for their arduous flights. Mr. Seebohm has taken our 

 Great Reedwarbler and other birds of the same genus 

 and shown how the form of the wing varies with the 

 extent of the migration. 2 



i Die Vogelwarte Helgoland, p. 27. 

 2 Siberia in Europe, p. 245. 



