Wonderful powers of sight are possessed by this bird. Its eyes are able to assume either a telescopic or a microscopic character, by means of a complex and marvellous structure, which can alter the whole shape of the organ at the will of the bird.
VULTURES.
Not only can the eye be thus altered, but it changes instantaneously, so as to accommodate itself to the task which it is to perform. A Vulture, for example, sees from a vast height the body of a dead animal, and instantly swoops down upon it like an arrow from a bow. In order to enable the bird to see so distant an object, the eye has been exercising its telescopic powers, and yet, in a second or two, when the Vulture is close to its prey, the whole form of the eye must be changed, or the bird would mistake its distance, and dash itself to pieces on the ground.
By means of its powerful eyes, the Vulture can see to an enormous distance, and with great clearness, but neither so far nor so clearly as is popularly supposed. It is true that, as soon as a carcase is discovered, it will be covered with Vultures, who arrive from every side, looking at first like tiny specks in the air, scarcely perceptible even to practised eyes, and all directing their flight to the same point. "Where the carcase is, there will the vultures be gathered together." But, although they all fly towards the same spot, it does not follow that they have all seen the same object. The fact is, they see and understand each other's movements.
A single Vulture, for example, sees a dead or dying sheep, and swoops down upon it. The other Vultures which are flying about in search of food, and from which the animal in question may be concealed, know perfectly well that a Vulture soars high in the air when searching for food, and only darts to the earth when it has found a suitable prey. They immediately follow its example, and in their turn are followed by other Vultures, which can see their fellows from a distance, and know perfectly well why they are all converging to one spot.
In this way all the Vultures of a neighbourhood will understand, by a very intelligible telegraph, that a dead body of some animal has been found, and, aided by their wonderful powers of flight, will assemble over its body in an almost incredibly short space of time.
The resting-place of the Griffon Vulture is always on some lofty spot. The Arabian Vulture will build within easy reach, the eagle prefers lofty situations, but nothing but the highest and most inaccessible spots will satisfy the Vulture. To reach the nest of this bird is therefore a very difficult task, only to be attempted by experienced and intrepid cragsmen; and, in consequence, both the eggs and young of the Griffon Vulture cannot be obtained except for a very high price. The birds are fond of building in the rock-caves which are found in so many parts of Palestine, and in some places they fill these places as thickly as rooks fill a rookery.
In Mr. Tristram's "Land of Israel," there is a very graphic description of the Griffon's nests, and of the difficulty experienced in reaching them. "A narrow gorge, with limestone cliffs from five hundred to six hundred feet high, into which the sun never penetrates, walls the rapid brook on each side so closely that we often had to ride in the bed of the stream. The cliffs are perforated with caves at all heights, wholly inaccessible to man, the secure resting-place of hundreds of noble griffons, some lämmergeiers, lanner falcons, and several species of eagle.... One day in the ravine well repaid us, though so terrific were the precipices, that it was quite impossible to reach any of the nests with which it swarmed.