WATER BIRDS 



noticed that a bar on one side was so thickly 

 covered with the great birds that no sand was 

 to be seen, while on the other that the broad 

 flat beach for at least a mile was thronged with 

 them, a great army of gray and white. Over- 

 head they were continually passing and re- 

 passing, drifting along before the wind or sail- 

 ing straight into the teeth of it. Physicists 

 have shown, it seems to me conclusively, that 

 an up-current is needed in these cases, where 

 gulls glide directly against a strong wind, as 

 they often do for miles close to steamers, ta- 

 king advantage of the up-currents there pres- 

 ent. Over land or sea, vmder other conditions, 

 it is rare that birds are able to glide far, for 

 up-currents, although common for shorter 

 spaces, are not so continuous as they are be- 

 side a moving steamer. Headley in his 

 " Flight of Birds " says: " In Algeria I once 

 saw two Eagles sail straight ahead against 

 the wind for about a mile and a half without 

 moving their wings till they reached a high 

 mountain ridge, blowing over which the wind 

 had got an upward trend." 



It is a difficult matter to estimate the num- 

 bers of gulls in these large flocks,— it is im- 

 possible to count them,— and I have adopted 



127 



