WATER BIRDS 



noticed that a bar on one side was so thickly 

 covered with the great birds that no sand was 

 to be seen, w^hile 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, under 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 " saj^s: '' 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 



