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. 
