Some people find a goat’s stare unsettling. That’s because a goat’s pupils are horizontal rectangles, not round like ours or vertical slits like a cat’s.

Why do goats have rectangular pupils? Goats are plant-eating prey animals, and they need to spot predators early. Horizontal pupils widen their view of the ground around them and cut down glare from the sun overhead.

A 2015 study led by UC Berkeley vision scientist Martin Banks compared 214 land species. It found that pupil shape is linked to an animal’s place in the food chain. Horizontal pupils are typical of grazing prey animals with eyes on the sides of their heads.

Banks also found that goats’ eyes rotate in their sockets when they lower their heads to graze. This keeps the pupils level with the ground, so the goat keeps its wide view of approaching danger.

According to the Berkeley team, each eye can rotate 50 degrees or more.

Goat Eyes vs Human Eyes

A goat’s eyes sit on the sides of its head, while ours face forward. That gives goats a much wider field of view but less overlap between the two eyes, so their depth perception straight ahead is weaker than ours.

Their horizontal pupils stretch that wide view even further. The shape lets in more light from the front, back and sides while blocking some of the bright light from above.

Goats do have a small blind spot directly behind them. Their view is very wide, but not a full 360 degrees.

The basic parts of the eye are the same in goats and people. Both have a cornea, an iris, a pupil, a lens and a light-sensitive retina at the back.

Benefits For Goats Having Rectangular Pupils

Spotting danger early is a goat’s first line of defense. Eyes on the sides of the head and horizontal pupils work together to give a panoramic view.

This pattern shows up in many prey animals. Predators tend to have forward-facing eyes for judging distance, though there are exceptions.

Horizontal pupils sharpen the image of the ground along the horizon, where predators usually approach. They also reduce glare from the sky, so the ground is easier to see.

Because the eyes rotate as the head drops, a grazing goat can keep watch while it eats.

Good eyesight alone won’t keep a goat safe. Goats are herd animals that rely on each other to watch for danger, and domestic goats need secure fencing and shelter from predators.

All goats have horizontal pupils, whatever their breed, size or eye color.

What Colors Do Goats See?

Goats see color, but not the way we do. Like most mammals, they have two types of color-sensing cones instead of our three.

This is called dichromatic vision. Animals with it see blues and yellows well but have trouble telling red from green.

To a goat, red and green likely look similar, much like they do for a person with red-green color blindness.

Are Goats the Only Animals With Rectangular Pupils?

No. Horizontal pupils are common in grazing prey animals, such as sheep, deer and horses.

Octopuses and some toads and frogs also have horizontal or rectangular pupils.

It is notable that animals as different as goats and octopuses share this shape. In each case, a slit-like pupil can open wide in dim light and close down to a narrow slot in bright light.

Sources

• Pupil shape linked to animals’ place in ecological web, UC Berkeley News
• Why do animal eyes have pupils of different shapes?, Science Advances