I40 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, too, that his 

 mandibles fly open at the moment the boom is 

 heard, although I cannot be sure such is the case. 

 Besides, the peculiar chuckle, 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 Spe-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 not 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. 



