312 BRITISH BIRDS. 
The presence of the Nightjar in a district is generally made known by its 
singular notes. These have been likened by numerous writers to the 
noise made by some kind of machinery. They remind one of the note of 
the Grasshopper Warbler, but are much louder and deeper. If tigers 
purr like cats, I should imagine they would make a noise something like 
the Goatsucker. Its ordinary note may be very closely imitated by 
sounding the letter 7 sufficiently rapidly to make the tongue vibrate, and 
then, endeavouring to give it a slightly guttural sound, making it occa- 
sionally swell and sink in loudness, and slightly alter in tone, as it is 
- produced by inhaling or exhaling the breath. The note is very powerful, 
and on a still evening may be heard at a long distance. This churring 
note is uttered at irregular intervals, and usually lasts a minute or so, 
sometimes as much as four or five minutes, and is said to be confined to 
the male bird, and only uttered when it is perched. It is generally heard 
in the dusk and at night; but in the height of summer, especially in the 
pairing-season, it is occasionally heard during the day. In addition to 
the notes already described, the male bird occasionally makes a whoop- 
like sound ; but how this is performed, whether by the throat or the wings, 
is at present unknown. It is often heard when the birds are chasing each 
other in early summer. 
The food of the Nightjar is supposed to consist exclusively of insects of 
various kinds. It is very fond of catching cockchafers, and eats many of 
the large moths and night-flying beetles; and Macgillivray discovered 
that it feeds on caterpillers. It is said to snatch the Ghost-Swift Moth 
from the grass-stems ; but more often takes this species as it flutters above 
them. The Nightjar is a voracious bird, and captures a great many insects 
in a single night. It is also said to eat slugs. The refuse of its food is 
cast up in the form of pellets. The bird has been said to hunt for its food 
with its large mouth wide open; but this is certainly an error. It can 
open and close its bill in a moment, and does so as occasion requires, 
resembling in this respect Swallows and Swifts. There has been much 
controversy as to the use of the large bristles at the gape of the Nightjar, 
and more as to the uses of the serrated claw. The bristles may aid it 
considerably in capturing its prey, and are usually found on the gapes of 
most insect-feeding birds; but there are many Nightjars in different parts 
of the world that have no such appendages. The use of the serrated or 
combed claw remains still unknown, though many ingenious theories have 
been invented to explain it. Some writers have thought that it was used 
to aid the bird in capturing its prey ; others have said that it was employed 
to comb out its long rictal bristles, or to rid its plumage of parasites ; 
whilst Naumann was of opinion that it was of service to the bird when 
perched lengthwise on the branches. 
The Nightjar may possibly pair for life; and each successive season 
