THE PHILOSOPHY OF MIGRATION. 85 



Geese, for instance, are noisy during Flight ; so too 

 are Waders. Crows, however, especially when 

 migrating by day, are silent birds ; but Larks, 

 whether on passage by day or by night, are inces- 

 santly calling to each other, and very frequently 

 burst out into song the moment they reach land 

 during daylight. Many a time the only sign on 

 earth that a great migration of birds is in progress, 

 is by hearing the varied and oft-repeated notes, 

 sounding faintly from on high as the armies of 

 birds pass on in the darkness overhead. 



A few words on Wind and Temperature will bring 

 these meagre remarks on the philosophy of a great 

 subject to a close. There can be no doubt that 

 wind has a great influence on the migratory move- 

 ments of birds. It is not every wind that is favourable 

 to Flight ; tempests arrest migration almost entirely ; 

 adverse winds retard it ; but a gale, if from a suit- 

 able quarter, often seems more to assist it than 

 otherwise. Strong head winds are always avoided 

 if possible, for the obvious reason that a long- 

 continued flight would be made with a maximum 

 of labour and a minimum of progress. A wind 

 blowing directly behind is also unfavourable to 

 Migration Flight, for the cold current blows up 

 through the plumage and chills the body of the 

 flying bird. The favourite wind is a shoulder wind, 

 what in nautical parlance is known as a " beam 

 wind," or a wind blowing more or less obliquely 

 across the line of flight. The direction of flight 

 is usually within three or four points of the wind. 



