130 THE FLIGHT OF BIRDS 



these Rooks never for more than an occasional half- 

 second lost command of their movements. The 

 Starlings were no less at their ease, so that, to my 

 thinking, this curious little problem of flight with a 

 gale blowing from behind is settled. Birds are 

 capable of such flight, and much enjoy it. But to 

 migrate in such wild weather would be a different 

 matter. It is no wonder that they do not choose 

 a dark, stormy night for a long oversea voyage. 



Undulating Flight without Movement of 

 the Wings. 



At one time I believed that this was possible when 

 the wind was blowing horizontally, but I now feel 

 sure that an upward trend is necessary. Take an 

 example that is often to be seen. The wind is 

 blowing at something like a right angle to the course 

 of a steamer, and the Gulls, which are following to 

 pick up any scraps that may be thrown into the sea, 

 soon recognise that there is a chance of saving their 

 muscles. There is an up-current of air on either 

 side of the ship, for the wind is, so to speak, bent 

 upward some little distance before it reaches the 

 obstruction. To start with, then, the Gull obtains 

 some slight elevation by means of a few strokes, then 

 he glides down a gentle incline in the direction in 

 which the ship is travelling. When close to the 

 water he turns and faces the wind, which, having 

 an upward trend, lifts him to the level from which 

 he has just descended. He then glides downward 

 again, and so the process goes merrily on. 



Were the wind a horizontal one it would, no doubt, 

 help the Gull to rise, but it would not make all 



