228 BULLETIN 17 6, UNITED STATES NATIONAL MUSEUM 



There is another note of the nighthawk very different in character, 

 an aeolian sound, produced by the rush of air through the primaries 

 of the wings at the termination of the extraordinary downward 

 pkmge executed during the courtship season. In order to see this 

 performance and to hear this peculiar and unique note to the best 

 advantage it is necessary to visit the vicinity of the nesting site. 

 Alexander Wilson (1828) described this note as a "loud booming 

 sound very much resembling that produced by blowing strongly 

 into the bunghole of an empty hogshead." E. H. Eaton (1914) 

 offers a modification of Wilson's description in stating that the note 

 is like that produced "by blowing across an empty bottle." T. G. 

 Gentry (1877) describes it as a sound resembling that "produced 

 by a tense cord set in vibration by a sudden gust of wind;" T. 

 Jasper (1878) states that it is a hollow whir like the rapid turning 

 of a spinning wheel, and F. A. Hartman (1914) describes it as a 

 "guttural 'woof.' " The note reminds W. A. Stearns (1883) of the 

 sound produced by a bellowing bull. In my field notes I have 

 described this note as a mufiled wT-r^T{i\i\r-oonk^ but sometimes more 

 nearly approaching sio-r^r,r^7'-ooonl\ the last syllable decidedly ac- 

 cented and produced with great resonance. There is nothing about 

 this note suggesting an explosive boom or bellowing. 



It has long ago been well established that this peculiar note is 

 not a vocal sound but one produced by the vibration of the primaries. 

 As keen an observer as Alexander Wilson (1828) stated that it is 

 "produced by the sudden expansion of his capacious mouth." Others 

 shared Wilson's view or thought that it was a sound produced by the 

 syrinx. After one has observed the performance it can be readily 

 understood how such an erroneous interpretation was made by the 

 earlier observers. The plunge takes place so quickly that it is only 

 by repeated observations made under the most favorable conditions 

 that the observer is convinced that the primaries are involved. 

 Audubon (1840) was the first to arrive at a correct explanation. 

 He writes that the source of the singular noise is "the concussion 

 caused, at the time the bird passes the centre of its plunge by the new 

 position of its wings, which are now brought almost instantly to 

 the wind, like the sails of a ship suddenly thrown back." This 

 observation with variation of its details has been made by numerous 

 subsequent observers. J. B. Canfiekl (1902) gives a description of 

 the performance as follows: "He suddenly paused and came soaring 

 toward me like an arrow. About fifty feet in front of me his wings 

 were lowered below his body, throwing them forward with the flight 

 feathers spread wide apart * * * His speed was so great that 

 the flight feathers vibrated like a loosely-stretched rubber band when 

 snapped with the fingers. This performance was repeated in front, 

 back, and beside me twelve times in all, never more than fifty feet 

 away, and as near as fifteen. In all cases the wings were in the 



