Figure 8 continued 



G. Juvenile Yellow-headed Blackbird; wind nil on ground behind trees, 15-20 m.p.h. 

 above tree level; bird climbed to about 150 feet and flew out of sight. 

 H. Adult male Pintail; wind 25 m.p.h.; bird flew at about 100 feet. 

 I. Juvenile Yellow-headed Blackbird; wind 15 m.p.h.; bird climbed to 150 feet. 



leg of a circle, however, the ground speed was reduced by the force of the 

 wind, just as forward motion over the ground was increased by the air flow 

 in every downwind turn. The circles remained constant to the air mass, but 

 were distorted relative to the ground and to the observer, this distortion 

 being proportionate to the strength of the wind. This was shown in the 

 hooded flight of a juvenile Yellow-headed Blackbird set free behind the 

 shelter of trees where there was no wind at ground level. When released, 

 it flew in well-defined circles until it climbed above the trees, where it met 

 a 15 m.p.h. wind. Thenceforward its circling continued at the same rate, but 

 the flight pattern described a series of widely separated loops (Figure 8, G). 

 The circle was not invariably the pattern in all hooded tests. Some birds 

 adopted flights that varied widely from the true circle (Figure 8, H, I); 

 but these variations, though individually distinct, always followed a pattern 

 of curves that carried the bird downwind from the starting place. In the 

 swift-flying birds, like the ducks, the flight did not fit into the circling pat- 

 tern as frequently as in the smaller species. This may have been because 

 they so often and so quickly flew out of sight that the true shape of the 

 flight could not be judged. One Redhead made a clean circle a mile in 

 diameter before flying out of sight (Figure 8, B), and three hooded Green- 



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