NIGHT HA WK. 
201 
flight, so characteristic of this species, then, darting suddenly in an oblique direction for 
a few feet, will emit his discordant squeak; when he will fly a few yards, only to repeat 
this performance, the notes being given after intervals of a few seconds. Every move¬ 
ments carries him upward, until he has reached quite an altitude, higher in day-light than 
in the evening, when down he plunges with half closed wings to within a few yards of the 
ground and, just as he extends his wings to turn upward again, comes the peculiar boom, 
so aptly described by authors as similar to the sound produced by blowing into the bung- 
hole of an empty barrel. 
Just how this sound is produced is not easily explained and has given rise to various 
theories. Some authors affirm that the air rushing through the loosened quills of the wings 
causes the noise. It is true that this explanation appears plausible but I am inclined to 
think that the sound is not produced mechanically, for reasons which I will now give. 
First, the noise is under the control of the will of the birds for they frequently dive in si¬ 
lence. This is one point but is not conclusive, as the quills of the wings might be made 
to change their position so that the sound would ensue at one time and be withheld at an¬ 
other, but a careful examination of the wings does not reveal any essential difference in 
structure from those presented by other members of the family. Under the microscope, 
the barbs of the quills are seen to be furnished with very long barbules which are pectina¬ 
ted on both sides for their basal two thirds, but this is also observable in the Whippoor¬ 
will and other allied species. The long filaments of the barbules causing the fringed wings 
in Owls and other birds, ensure a silent passage through the air and consequently the 
flight of a Night Hawk is particularly noiseless as any one who has had one pass close to 
him, will remember. Thus it will be seen that the facts of the case do not at all support 
the theory. The idea that the air rushing into the suddenly opened mouth causes the sound 
is too improbable to notice and therefore I will hasten to explain what I consider the true 
origin of the booming note of the Night Hawk. I say note, most advisably, for I am cer¬ 
tain that this singular cry is vocal. As will be seen upon referring to the generic charac¬ 
ters which I have given, there are but two laryngeal muscles. The broncho-trachealis 
posticus is not strong in the male and is scarcely developed in the female. I therefore 
judge that this produces the squeak, but the sterno-trachealis which acts as a relaxor to 
the tympaniform membrane, is very thick and strong, just as it is in the Whippoorwill and 
Chuck-will’s Widow. In both these species, it is quite probable that the peculiar notes 
which are so decidedly in a minor tone, are caused by this muscle acting upon the mem¬ 
brane of which I have spoken above. Now I can see no reason why the note of the Night 
Hawk should not be produced by the action of the same muscle, for it is also in the minor 
tone and if any of the louder cries of the Whippoorwill or, better, of the Chuck-will’s Wid¬ 
ow were prolonged, they would not sound very unlike the boom of the species under con¬ 
sideration. 
I scarcely think that the Night Hawks are abroad all night, but that they only fly 
during the dusk of evening, being more active in hunting, however, as it grows dark; in 
fact the males remain high in the air until long after sunset, when they will descend and 
fly rapidly along close to the ground. They feed upon insects which they capture during 
BIRDS OF FLORIDA. 
