416 CORACIIFORMES CHAP. 
noptilus nuttalli. The characteristically soft plumage shews an 
intricate mixture of brown, grey, fawn, black, and white, and is 
ordinarily barred and minutely freckled, but frequently patched or 
spotted with white ; it 1s, however, impossible in a limited space to 
describe the species in detail, though it may be noticed that several 
have reddish nuchal collars; and some exhibit rufous and grey phases 
—unless, as may be the case, the rufous forms are females—while 
others from arid districts have a protective coloration of a more 
or less sandy hue. In the Podargidae large powder-down patches 
occur laterally on the rump, in the Nyctibiimae on the breast and 
sides. The sexes are often alike, the young either resembling the 
female, or assuming the full plumage at once. Lyncornis, Otophanes, 
and Batrachostomus have head-tufts like those of some Owls, the 
constituent feathers in the last genus being bristle-pointed. 
Nightjars are found in most parts of the world, while the 
northern species habitually move southwards for the winter, 
Podager and Chordiles, at least, flocking in August and 
September. The most typical forms are distinctly crepuscular, 
and pass the day—as our british bird does—quiescent on the 
soul, or upon some post or fence, often concealing themselves 
below shrubs or herbage, or in hollow stumps. At such times 
they will almost permit themselves to be trodden upon before rising 
from the ground, and sit with their eyes closed; on branches 
the body is ordinarily placed lengthwise, but on thin palings 
or wire this is of course impossible. yctidromus exhibits more 
terrestrial habits, and walks instead of shuffling; the American 
“Bull-bat” (Chordiles virginianus) hawks in the full glare of 
the sun. The more diurnal species frequently rise to a consider- 
able height in the air, sailing backwards and forwards with an 
easy, flapping motion, descending with undulating swoops, or 
remaining momentarily poised aloft, and then darting suddenly 
upon their prey; the flight of their nocturnal allies is weaker 
and more lowly, being jerky, twisting, and erratic. Some forms, 
if not all, when inspecting an intruder turn the head almost 
completely round. The vibrating sound often accompanying 
the passage through the air may be produced by the wings 
coming into contact, as is the clapping noise occasionally heard ; 
but the cause is not certainly ascertained, nor is that of the far- 
resounding “churr” uttered by the male of the Common Nightjar 
while stationary. The birds are, however, often quiet on the 
