BIRDS OF PREY. 137 
mit a great deal of light; they are also surrounded with 
a disk of feathers of a light color, which serves to direct 
the light, striking it in upon the eye. The nictitating 
membrane is very conspicuous, it being needed to shut 
out some of the light in broad day; to open its eyes 
widely then, and without the covering of this membrane, 
would dazzle the Owl exceedingly. Its head is very 
large and round, which is owing mostly to some cells 
that are connected with the organ of hearing, rendering 
that sense very acute; this is of essential service to it in 
taking its prey by night. Owls are the only birds that 
have an external ear, § 206. It is covered by feathers, 
and in some species by a sort of lid, which the bird can 
open or shut at pleasure. | 
232. The plumage of the Owls is very peculiar. It is 
downy, partly to keep them warm, but mostly to enable 
them to approach their prey noiselessly. Their flight is 
so noiseless that they seem borne along on the air like 
a tuft of down. The food of the larger species consists 
of hares, rabbits, fawns, birds, etc., and that of the smaller, 
of mice, rats, moles, small reptiles, and the larger insects. 
They take these either by night or in the twilight; and 
we find this family most abundant in those portions of 
the globe where the twilight is most prolonged—the 
cold and temperate regions. There are some aberrant 
species in which the habits are diurnal more than noc- 
turnal, and, consequently, the characteristics mentioned 
are not fully developed in them.. The typical species, in 
which the development of these peculiarities is complete, 
scarcely move during the day. They remain at rest upon 
their perch, with eyes half closed, and an amusing air of 
gravity ; and when aroused in any way they do not fly 
off, but raise themselves up, and assume grotesque atti- 
tudes, making ludicrous motions. 
233. The Barn Owl, Fig. 114 (p. 138), is widely dif- 
fused through the temperate regions of Europe and this 
country. It is a very useful animal in destroying rats 
