140 IN BIRD LAND. 
considerable study of this queer performance, I am 
persuaded that it is a vocal outburst, produced 
either for its musical effect (though it is far from 
musical), or else to give vent to the bird’s exuber- 
ance of feeling as he makes his swift descent. 
His thick, curved bill seems admirably adapted 
to produce this sound, as do also his arched throat 
and neck. It has seemed to me, 400, ‘that jhus 
mandibles fly open at the moment the boom is 
heard, although I cannot be sure such is the case. 
Besides, the peculiar chuck/e, previously referred to, 
had about it a quality of sound suggestive of kin- 
ship with the bird’s resounding boom. ‘The hollow, 
wheezy alarm-call of the young birds, heard on 
several of my visits to the nest in the marsh, cor- 
roborates this theory. But there is still further proof 
that this hypothesis is correct. The night-hawk 
often makes his headlong plunge without booming at 
all, but merely utters his ordinary rasping, aerial call, 
which has been translated by the syllable Sfe-ah. 
Then he sometimes combines the two calls, and on 
such occasions both of the sounds are uttered with 
a diminished loudness, as one would expect if both 
are vocal performances, but as one would zo¢ expect 
if the booming were made by the concussion of the 
bird’s wings with the resisting air, as some orni- 
thologists suppose. ‘The female sometimes booms, 
but her voice obviously lacks the strong, resounding 
quality that characterizes the voice of her liege lord. 
