Have you ever looked closely at a goat or sheep and noticed their weird rectangular eyes? I hear guests commenting on them every few weeks; some people love them, some people are disturbed by them, I think they’re awesome!
Ungulates (hooved animals) are prey animals and need to have a great field of vision to avoid being snuck up on by a predator while they’re grazing. The rectangular pupil of the sheep and goats allow them to see in nearly a full circle around them: 320-340 degrees! This has some disadvantages, though. The flattened pupil disallows goats and sheep to look upwards or downwards without raising or lowering their heads. This is why, if you reach out to pet a goat’s head, they’ll often step back and look up at your hand. They can’t see you when you’re directly above them.
Equine, cattle and pigs have large eyes with round pupils on the sides of their heads, which gives them around 300 degrees of vision but they can see a little better above and below their eye level than goats and sheep can. They still need to raise or lower their heads to gauge distance above and below eye level because depth perception exists only where the vision from both eyes cross. With one eye on each side of the head, the area in front of the animal where the vision crosses (called binocular vision) is fairly small: 20-60 degrees for sheep and goats, and 60 degrees for equine, cattle and pigs. These animals also have blind spots directly in front of their face and directly behind their back legs. This is why walking behind a horse or steer could get you hurt. They can hear you back there, but not see you. The animal may kick to protect itself.
Predators don’t need to see all the way around their bodies as much as they need to be able to gauge distance in front of them. Humans and bears have eyes with round pupils on the front of their heads so that more of the vision from each eye overlaps and there’s a larger area of depth perception. Humans can see about 120 degrees around themselves but have 100 degrees of binocular vision.
Check out these other cool animal department eyes! Do you know to whom they belong?