BIRD NOTES. 79 



door of that "capacious mouth while passing through the air." 

 Wilson so inferred, and significantly compared the noise to that 

 produced "by blowing strongly into the bung-hole of an empty 

 hogshead." Audubon, I believe, was the first to suspect the wings 

 of the bird as the resonant source, presumably the long quill 

 vanes ; and there would seem to be many circumstances to ver- 

 ify his conjecture, the sudden horizontal tilt of the wings which 

 determines the upward finish of the swoop, and which is always 

 simultaneous with the "boom," tending to reinforce his theory. 

 The fact which I have discovered, that a fair imitation of the 

 sound can be produced by blowing between the leaves of a book, 

 loosely held, would seem to suggest a similar vibratory origin. 



On two occasions, moreover, I have observed a quite similar, 

 though, of course, diminished sound, produced by swallows, and 

 in both cases unquestionably proceeding from the wings and dur- 

 ing a quick curvet of flight as they dove about the " well-dissem- 

 bled fly" which I swung aloft from my fishing-rod. 



I have never attempted the test, but have often wondered 

 whether a nighthawk's wing, skilfully adjusted to a slender fish- 

 ing-rod and swept through the air, might not be made to give 

 forth that veritable twang ! 



Once, while passing through a pasture, I almost stepped upon 

 what appeared to be an irregular piece of bark which had fallen 

 from a neighboring fence-rail. It lay there in the grass, and only 

 the effect of exact symmetry in form, accentuated by the white 

 spots upon its pinions, dispelled the illusion for it was a night- 

 hawk. The position of the bird showed at once something un- 

 usual. According to its habit, by day, its eyes were closed to 

 a mere crevice. Half -supposing the bird to be dead, I stooped 

 to pick it up, but only to be met with an angry flutter, the bird 

 darting at me, showing the full interior of his throat and uttering 

 a hoarse screech, while the black depths of the now widely open- 

 ed eyes simultaneously lit up with a lurid rosy glare. This was 

 repeated at my slightest movement towards the wounded bird, for 

 I soon discerned that its wing was broken, presumably a cruel 

 penalty for a heedless swoop against a telegraph-wire overhead. 



