BIRDS 



249 



rapid beating of the wings of quail and grouse; also of 

 wild ducks; the slow, heavy, flapping of the larger hawks 

 and owls, and of the crows; and the splendid soaring of 

 the turkey-buzzard and of the gulls. This soaring has 

 been the subject of much observation and study, but is 



Fig. 203. — Gulls soaring. (Photograph by Otto von Bargen, on San 

 Francisco Bay; permission of Camera Craft. ) 



still imperfectly understood. The soaring bird evidently 

 takes advantage of horizontal air-currents, and some 

 observers maintain that upward currents also must be 

 present. The principal hopes for the invention of a suc- 

 cessful flying-machine rest on the power of soaring 

 possessed by birds. The speed of flight of some birds 



