You cannot deny that sheep are pretty interesting animals. Economically they are important as a source of meat and wool, and the latter has been loved for its ability to make garments that will keep you warm even when they are soaking wet. No other animal has hair quite like them.
And speaking of unique physical characteristics, have you ever looked closely at a sheep’s eyes?
If you have, you will have undoubtedly noticed that peculiar, oblong rectangular pupil. It’s definitely different, and you might even find it a bit unsettling.
Just why do sheep have rectangular pupils anyway?
Sheep have rectangular pupils due to the arrangement of their eye musculature, and because it grants them a much wider field of view, an important trait for a prey animal.
Don’t let that odd look bother you; sheep see more or less like you and me do, and their vision is surprisingly excellent in some ways, though limited in others.
You might find the following facts about a sheep’s vision interesting, and at any rate it will help you understand them a bit better. Keep reading to learn more.
Sheep have Rectangular Pupils Because of their Eye Musculature
There are many pupil shapes to be found in the animal kingdom. Many animals have round pupils, some have vertical slits, and a few have something truly weird like a cuttlefish’s w-shape.
But sheep have “rectangular” pupils, though they are really more of a blunted oval. This is because of their eye musculature.
The muscles that control the shape of the pupil are located around the edge of the iris, and in sheep, these muscles are arranged in a way that it results in a rectangular pupil.
This unusual pupil shape provides some benefits for sheep that help them better adapt and thrive in their part of the food chain namely by helping them to see in low light conditions and giving them a much wider field of view than most other mammals.
It also makes them look pretty unique!
Sheep are Prey Animals, So They Need to See Predators Early
Sheep, as you doubtless know, are prey animals. They might be deadly “predators” of grass and plants, but the real predators always have sheep on their menu.
It isn’t hard to see why: any sheep has plenty of meat, is not very fast, and can barely defend itself in any meaningful way. For large and capable predators, sheep are a score!
Accordingly, a sheep’s best defense is seeing trouble coming early so they can alert the flock and start to get away, perhaps spoiling a sneak attack and giving them a chance to live another day.
A sheep’s rectangular pupils help it see predators early by giving them several advantages when it comes to early detection.
A Sheep’s Pupils Help Grant it a Wide Field of View
Perhaps the single most important asset granted to sheep by their pupils, and in conjunction with the placement and spacing of their eyes, is an extremely wide field of view.
A sheep’s eyes are placed on the sides of their head, and this gives them a field of view, allowing them to observe almost the entirety of their surroundings without moving their head.
This is important for several reasons: It helps sheep spot predators approaching from almost any direction early, and it also means that a group of sheep can keep an eye out for dangers with near total covering while grazing.
Even if a sheep is distracted by something, it can still keep its eyes in the back of its head, so to speak!
How Wide is a Sheep’s Vision Arc?
A sheep’s field of view is anywhere from 270 and 320 degrees on the horizontal plane. This means that a sheep can see almost all the way behind itself without moving its head!
In comparison, humans have a horizontal field of view of around 200 degrees, while many predators like cats have a slightly narrower field of view of just under 200 degrees.
While a sheep’s field of view is impressive, it isn’t perfect. Remember that a sheep’s eyes are on the sides of their head, so they don’t have binocular vision. This makes it harder for them to accurately judge distances.
Sheep are Very Good at Detecting Motion
Sheep also have acute visual capability when it comes to detecting motion. Again, this is definitely a prey animal adaptation that has come about because of the critical need to spot predators early.
Sheep have special adaptations that help them see moving objects, and combined with their excellent field of view most predators will be hard-pressed to close in on them.
Especially when a sheep is nervous or alerted the slightest hint of a threat moving is enough to send them running, and this is good for the sheep since many predators will give up if they think their prey is aware of them.
Fun Fact: A Sheep’s Eyes Rotate to Stay Level with the Ground
To me, this is the coolest bit of trivia about sheep’s eyes there is: Their eyes actually rotate axially in their sockets to stay level with the horizon.
Sound nuts? It’s true, but it is easy to see, and once you do you will start questioning your whole life, especially if you have spent a lot of time around sheep and other animals with this quirk.
Pay attention to your sheep the next time it puts its head down to the ground from a standing position. Notice how the orientation of the pupil doesn’t change? That’s it!
This means a sheep’s perception of the world is not altered or degraded when its head changes position. Compare that to your own view when you tilt your head too far to one side; gets a lot harder to keep things in perspective, yeah?
All of these factors together make it very difficult for predators to take sheep by surprise, and the rectangular shape of their pupils is a big component of that.
So, the next time you see a sheep grazing peacefully in a field, remember that those unassuming eyes are actually on high alert, keeping watch for any danger that might come their way.
Disadvantages of Rectangular Pupils
It isn’t all good news when it comes to a sheep’s vision, and though rectangular pupils have some advantages they also have disadvantages, too.
Probably the biggest one is the fact that sheep have generally poor perception up and down, compared to left and right on the horizontal plane.
Theoretically, a predator approaching from above, say in a tree or on a ledge, or one from below would have an innate advantage over a sheep’s sharp vision.
Sheep also don’t see great at night. They see pretty well, mind you, at least better than you and I, but their usual predators often have a big advantage over them in the night.
Coyotes and wolves, for example, can see significantly better than sheep in low-light conditions. This makes it easier for either to take down sheep at night, which is one reason why they are such a problem for ranchers.
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Tom has built and remodeled homes, generated his own electricity, grown his own food and more, all in quest of remaining as independent of society as possible. Now he shares his experiences and hard-earned lessons with readers around the country.