BIRDS OF PREY 
281 
themselves away in hollow trees or old ruins, into which the unwelcome 
light cannot penetrate; and it is not until some little time after sunset 
that they make their appearance. Then through the hours of night 
they hunt for prey, and can see their victims as clearly in the darkness 
as hawks can in broad day-light. Now, it is evident enough that the 
eyes of the owls must be very differently formed from those of the 
hawks, for otherwise they would be of no use at all after nightfall. 
And, when we come to examine them, we find at once that such is the 
case. Not only are their eyes very large themselves, but, as you must 
have noticed, they are surrounded by a kind of circular ring, sometimes 
composed of white feathers and sometimes of brown. 
THE SECRETARY BIRD 
If the thick plumage of the owl's head were all set in the usual 
manner, the feathers would project so far in front of the eyes that the 
bird would have scarcely any range of sight. But the curious feathery 
circle which surrounds the owl's eyes serves as a narrow slit in a deep 
window casing, and enables it to see in all directions; so that, without 
moving its head, it is able to keep watch over a very large extent of 
country. 
In other parts of their structure the owls are not at all unlike th<? 
