Human workers doing this type of work need frequent and long rest periods. A test using birds for this task proved that birds could work longer and be much more accurate. Geese have been taught to eat the bad insects from crops while leaving the good insects alone. Their eye sight seems to be suited to this task. The position of a bird's eyes on its head varies by type of bird.
Birds of prey have wider heads with the eyes set apart and facing forward, similar to humans.
This gives them binocular vision or depth perception and enables them to judge the speed and distances of prey and other objects. Birds such as parrots, which are prey for other animals, usually have eyes set on the side of the head. This gives the bird better peripheral vision and enables it to detect danger from a wider field of vision. Birds can move their eyes a bit, to extend their range of vision, but do not have the extensive ability of some reptiles to rotate the eyes. There are a number of diseases which can affect the eye, such as cataracts, conjuntivitis and absesses.