546 REPTILES AND BIRDS. 
twilight, owitg to the pupils of their eyes having enormous powers of 
dilatation. ‘They consequently remain hidden in their retreats while 
the sun is high, and do not begin to hunt until the luminary has 
approached the horizon, when they are able to distinguish with 
surprising clearness the creatures on which they prey. 
We are not, however, bound to believe that these birds can see 
in the midst of perfect darkness. When the night is thoroughly 
obscure they become subject to the law common to all. They mani- 
fest the greatest amount of activity when the moon diffuses her light 
over the earth; for then they revel in their destructive instincts, 
levying a heavy tax on all weaker animal life. The epithet of “noc- 
turnal,” which is applied to them, is, therefore, not strictly accurate, 
and must not be taken literally. 
Owing to the large cavities existing in their skulls, which com- 
municate with the internal ear, and increase the capacity of this 
organ, the Raptores have the sense of hearing strongly developed. 
Their plumage is streaked with diversely-arranged markings, and 
is as soft and delicate as the down of fledglings. ‘These peculiarities 
are probably owing to the special conditions of their existence. 
Constantly deprived as they are of the rays of the sun, the action of 
which upon colour of plumage cannot be doubted, they are not » 
arrayed in those splendid hues which clothe diurnal birds of tropical 
regions. 
Owing to the structure and nature of their feathers, nocturnal 
birds of prey fly without noise. ‘Thus they are enabled to pounce 
unawares on their victims, seizing them before they have any idea 
of necessity for escape. When they capture prey, it is at once 
devoured ; an easy matter, on account of the enormous expansion of 
their bills. Their stomach afterwards separates the indigestible parts, 
such as bones, hair, and feathers, and when these are rolled together 
in the shape of a ball or pellet, they are ejected by vomiting. 
Diurnal birds of prey which subsist on living animals also possess 
this peculiarity, 
With the exception of the Barn Owl, all nocturnai birds of prey 
lay eggs of a spherical shape. ‘They live in couples, only assembling 
in flocks at the epoch of migration ; they never, however, hunt in 
common. ‘They do not build any nest, but deposit their eggs in 
cavities in old trunks of trees or ruined habitations. ‘They exhale a 
disagreeable foetid smell, which no doubt is produced from their diet 
being exclusively animal. 
Unless forced, none of the members of this sub-order come out 
of their roosting-places during day. When compelled by circum- 
