202 



BRITISH BIRDS. 



and the right raised ; the bird is therefore sweeping round 

 to the left. I have seen birds when thus suddenly alter- 

 ing the direction of their course actually exceed the 

 vertical position, turning the plane of their surface 

 through an angle of about 105°, thus making an angle 

 of about 75° with the horizon, their backs then, of course, 

 being on the under side. 



FIGURE 5. — NEARLY VERTICAL IN POSITION. 

 {Photographed by Bentley Beetham.) 



The question of air-currents is of paramount importance 

 in flight, though it is probable that owing to their invisi- 

 bility we have as yet little idea of how extensive and acute 

 these movements are. If, however, we watch small 

 companies of Gulls flying leisurely in the same direction. 



