English translation by Michael Eabry
Tomō Yoshino (Chief in charge of cranes, Kushiro City Zoo)
When guiding visitors at the crane center or zoo, or just while walking there, I sometimes hear a voice calling to the red-crowned cranes, “face this way” or suchlike. So, what does it actually mean for a Japanese crane to be “facing this way”?
Birds’ vision has developed to look out for food or for enemies. The eyeballs are large and fit perfectly into the eye-socket in their skull, the orbital bone. When looking at something, humans move their eyeballs whereas birds move their necks, not their eyes. Also, the human eye is in the front of the face, whereas birds generally have eyes outside or on the side of the face. In any case, birds can’t move their eyeballs like humans, so they won’t reveal the whites of their eyes. There are times when it looks like you can see the whites of their eyes showing, but what you’re seeing is a transparent or translucent film inside the eyelid called the nictitating membrane. For example, it can be seen when they blink or when putting their faces underwater for protection of their eyes.
Looking at objects with both eyes is called binocular vision; in this case, the range of vision (field of view) at any one time is narrow. That said, objects appear three-dimensional, making it easier to get a sense of how far away they are. For example, the eyes of birds of prey, such as owls, hawks and peregrine falcons, point forward and are able to take in a wide range of binocular vision, which helps them to chase and catch their prey. Sparrows and pigeons, on the other hand, have eyes on the sides of their faces which, while affording limited binocular vision, can instead, with one eye, take in a broad range of view, which means that they can more easily spot enemies.
Red-crowned cranes have eyes on the sides of their faces, just like small birds, so their range of binocular vision is narrower than that of birds of prey and more suitable for observing with one eye. Cranes sometimes move their heads to one side in order to look up at the sky; and they move their heads back and forth while walking so that their surroundings don’t appear blurred; but when we look closely, the position of their head hardly changes at all. The reason cranes appear to face side-on is to get a clear view so that, in actual fact, they’re already looking at visitors. Note however that, in approaching people face-on, it means that the crane intends to peck; the crane’s crown is probably bright red and excited and in that case, please do not approach or touch the fence as it is dangerous.