280 BULLETIN 17 6, UNITED STATES NATIONAL MUSEUM 



always in a liurry ; it seems to be moving tliem up and down as fast 

 as it can; it often rocks from side to side, as it turns this way and 

 that, and ever seems to be trying to fly a little faster. 



Sutton (1928), in an able study of the swift's flight, aided by ex- 

 amination of captive birds, states that "no intermediate, half-spread 

 position [of the wing] was ever maintained in healthy individuals. 

 In fact, such an intermediate position seemed impossible [on account 

 of anatomical structure]. * * * 



"It may be stated broadly, therefore, that the Chimney Swift wing, 

 so far as its spreading is concerned, has but two normal positions; 

 one, folded at rest, the other, open for flight, whether that flight be 

 rapid forv/ard flapping, soaring, coasting, or even sudden descent." 



One evening Dr. Sutton, standing at the mouth of a chimney while 

 swifts were going to roost, watched the birds enter, within arm's 

 reach. Describing this experience, he says : 



I was amazed at their precision and speed. As a rule, they slowed up 

 abruptly just before making the final plunge, this being accomplished by a 

 spreading and lowering of the tail, and by rapid, vigorous, downward and 

 forward strokes of the wings, during which the loosely and widely spread 

 primaries seemed to aid in checking the speed. When a proper point above 

 the mouth of the chimney was reached the birds suddenly pressed the spread 

 tail downward as far as possible, and with oiitstretched wings high above the 

 back, still loosely fluttering, through an arc of about forty-five degrees, either 

 dropped directly, turned jerkily from side to side, or twirled gracefully down- 

 ward into the chimney. 



Again, in the morning, peering down the chimney as the birds 

 emerged, he says : "I was surprised to see that the birds were flying 

 almost directly forward, but in an upward direction. Their bodies 

 were not in a horizontal position ; they were almost vertical, and the 

 whole spectacle gave the impression that the birds were crawling up 

 invisible wires." 



' For years there has been a controversy concerning the swift's 

 flight. Some observers held that the swift moved its wings simul- 

 taneously, like other birds ; others believed that the wing beats were 

 alternate, like the strokes of a double-bladed paddle. It is easy to 

 see how confusion between fact and appearance might arise. Swifts 

 do appear to fly with alternate wing beats, but chiefly, if not wholly, 

 when the birds tilt to one side in making their quick turns. Then one 

 wing appears to be up and the other down, and as a matter of fact 

 such is the case in reference to an imaginary line drawn across the 

 swift parallel to the ground — one wing is above the line, and the 

 other is below it. But the bird being tilted to one side, in order to 

 show the relative position of one wing to the other, we must allow for 

 the tilting, and we must draw the imaginary line, not parallel to the 

 ground, but through the short axis of the bird^s body. The observer. 



