24 Introduction. 



circles at an immense altitude can distinguish his prey on the 

 ground, without the aid of any other faculty than his eyes, as 

 has been clearly proved by experiment ; the lordly eagle soaring 

 amid the clouds seems to prefer that elevated station, whence to 

 seek some victim on the earth, and his wonderful power of vision 

 seldom fails to discover the desired object far below; the kestrel- 

 hawk, with which all are familiar, balances himself in the air at a 

 considerable height, while his piercing eyes search the ground 

 below for the mice which constitute his food : these are all diurnal 

 birds of prey, and are especially noted for the keenness of their 

 vision ; but not less extraordinary is the eye of the owl, which 

 seeks its prey by twilight, and cannot endure the full glare of 

 day; should any accident expose him to the light of the sun, 

 he either closes his eyes entirely or defends them with a curtain 

 or blind, which is an internal eyelid, and which he can close in 

 an instant. At such times he presents but a grotesque and 

 foolish appearance ; but see him as he emerges from his hollow 

 tree, or the ivy-clad ruin in the deepening twilight ; watch him 

 as he regularly beats the field, and quarters it like a pointer; see 

 him suddenly drop upon the unfortunate mouse that was hurry- 

 ing through the grass, and judge what acuteness of vision must 

 be there. In the nocturnal species the eyes are usually directed 

 forwards, and are brighter, larger, and clearer than those of the 

 diurnal birds, and thus, from their size, position, and construc- 

 tion, are admirably calculated for concentrating the dim rays of 

 twilight. In the other Orders we do not expect to find such 

 wonderful powers of sight, for their habits do not require it ; yet 

 here, too, we shall often find considerable swiftness and extent of 

 vision. The fly-catcher will sit perched on a twig, and suddenly 

 dart upon an insect passing often at a considerable distance, 

 which we are wholly unable to perceive. The bold and sagacious 

 raven and the destructive carrion-crow have been famed for their 

 far-seeing propensities. The rook, too, has the same property; 

 for which cause we may constantly see the dull- eyed starlings 

 attaching themselves to their society and relying on these 

 excellent sentinels, feeding in greater security. The swift, 



