Another peculiarity of the owl lies in the position of its eyes. These are forwardly directed. In most birds the eyes are placed at the side of the head, so that owls alone among the feathered folk can truly be said to possess faces. The position of a bird’s eyes is not the result of chance or accident. A creature whose eyes are forwardly directed can see better ahead of him than he could were they placed at the sides of the head, but he cannot see what is going on behind his back. Animals whose eyes are at the side of the head have a much wider range of vision, for the areas covered by their visual organs do not overlap. Such creatures cannot see quite so well things in front of them, but can witness much of what is going on behind them. They are therefore better protected from a rear attack than they would be did their eyes face forwards. The result of this is that, if we divide birds and beasts into those which hunt and those which are hunted, we notice that in the latter the tendency is for the eyes to be placed at the sides of the head. They thereby enjoy a wider range of vision, while in the former the tendency is for the eyes to be so situated as to enable them best to espy their quarry. Compare the position of the eyes in the tiger and the ox, in the eagle and the sparrow. The tiger and eagle have little fear of being attacked, so have thrown caution to the winds and concentrated their energies to equipping themselves for attack. In owls the eyes are more forwardly directed than in the diurnal birds of prey, because they have to hunt their quarry under more difficult conditions. Even when its ears inform the owl that there is some creature near by, it requires the keenest eyesight to detect what this is. The position of a bird’s eyes is determined by natural selection. With colour and such-like trifles natural selection has but little to do. It works on broad lines. It determines certain limits within which variations are permissible; it does not go into details. So far as it is concerned, an organism may vary considerably, provided the limits it defines are not transgressed. This statement will not meet with the approval of ultra-Darwinians, but I submit that it is nevertheless in accordance with facts. If we try to account for every trivial feature in every bird and beast on the principle of natural selection, we soon find ourselves lost in a maze of difficulties.
It is because the eyes of owls are forwardly-directed that they are such easy birds to mob. They can see only in one direction—a limitation which day-birds have discovered. The result is that when the owls do venture forth during the daytime, they come in for rough handling. The position of the eyes in the owl would lead us to infer that the bird has but few enemies to fear, and, so far as I am aware, there is no creature which preys on them, except, of course, the British gamekeeper. Why, then, are owls not more numerous than they are in those countries where there are no gamekeepers to vex their souls? The population of owls must of course be limited by the abundance of their quarry. But there is more than enough food to satisfy the hunger of the existing owls. What, then, keeps down their numbers? Mr. F. C. Selous has asked a similar question with regard to lions in Africa. Even before the days of the express rifle lions were comparatively scarce, while the various species of deer roamed about the country in innumerable herds. The answer must, I think, be found in the intensity of the struggle for existence. Nature balances things with such nicety that the beasts of prey have their work cut out to secure their food. The quarry is there in abundance; the difficulty is to catch it. If this be so, it follows that the weaker, the less swift, the less skilled of the predaceous creatures must starve to death. In that case the lot of birds and beasts of prey is a less happy one than that of their victims. These latter are usually able to find food in abundance, and death comes suddenly and unexpectedly upon them when they are in the best of health. How much better is such an end than death due to starvation?
In most birds the opening of the auditory organ is small; in owls it is very large and is protected by a movable flap of skin, which probably aids the bird in focussing sounds. In many species of owl the two ear-openings are asymmetrical and differ in shape and size. This arrangement is probably conducive to the accurate location of sound. Want of space debars me from further dilating upon the wonderful ear of the owl.
In conclusion, mention must be made of the flexible wing feathers, and their soft, downy edges. Air rushing through these makes no sound. Hence the ear may not hear, but
“The eye
May trace those sailing pirates of the night,
Stooping with dusky prows to cleave the gloom,
Scattering a momentary wake behind,
A palpable and broken brightness shed,
As with white wings they part the darksome air.”