Here’s How Chickens Watch for Predators

Compared to a human, a chicken’s eyes are about 25 times bigger relative to the size of its head. The chicken’s eyes don’t look so large because they’re partly hidden behind flesh and feathers. But those big eyeballs take up so much space inside the skull that they leave little room for muscles. As a result, the eyes haven’t much leeway to move within the eye socket. So, when a chicken wants to focus on something, instead of moving its eyes, it moves its entire head.

Watching for Predators

Unlike a human’s forward oriented eyes, a chicken’s eyes are on the sides of its head. Eyes on the sides give the chicken a greater range of peripheral vision, but a smaller range of binocular vision, compared to creatures (including humans) with front facing eyes that both focus on the same thing.

So, unlike a human, the chicken sees two different things at the same time, giving it something of a panoramic view. The only place where a chicken sees the same object with both eyes is directly in front of its beak, which allows it to accurately peck a bug or a kernel of grain.

While the chicken is busy pecking on the ground, its panoramic view lets it see what’s happening along both sides and to the rear without having to turn its head. That way chickens can watch for predators at the same time they fill their crops.

However, the chicken has a blind spot straight ahead. That’s why a chicken turns its head to see something approaching it from the front. Whether the chicken turns its head to the right or to the left depends on what it’s trying to see.

Dual Eye System

Like other birds, a chicken has a right-eye system and a left-eye system. Each system has different and complementary capabilities.

The left eye transmits information to the right side of the chicken’s brain, and the right eye transmits information to the left side of the brain. The right-eye system is less easily distracted as it focuses on close-up activities, such as looking for tasty treats on the ground.

The left-eye system pays more attention to distractions, such as an unusual movement that could signal the approach of a predator. The left-eye system works best for activities involving depth perception, so a chicken seeing a hawk approaching is likely to peer warily at the raptor out of its left eye.

By noting the direction and speed of approach, the left-eye system (right side of the brain) decides how the chicken will respond. If the appropriate response is fear, the left-eye system looks for an escape route.

This dual eye system also gives a chicken the ability to sleep with one eye open. It can therefore rest one side of its brain, while the other side remains vigilant.

Day Vision

The chicken’s eyes are designed for seeing during the day, when chickens primarily eat and watch for predators. Daytime vision relies on cones, a type of light receptor in the eye’s retina. The light receptors in a chicken’s eyes are about 80 percent cones, compared to a human’s meager 5 percent cones.

Cones are most effective in bright light. They are essential for detecting color, which helps the bird find edibles. Chickens have better color vision than most animals, including humans. Where humans see three wave lengths — red, green, and blue — the chicken sees one more. The chicken’s eyes are additionally sensitive to the ultraviolet spectrum.

Cones also help the bird select healthy mates, based in part on the degree of pigmentation in the potential mate’s feathers. Pigment relates to a feather’s ultraviolet reflectance, which in turn relates to the chicken’s immune responsiveness. With the chicken’s superior ability to see plumage colors that are invisible to humans, can you imagine how much more beautiful chickens look to other chickens!

Chickens also have a double cone receptor, which helps them detect motion better than we humans can. They don’t, however, see things well that aren’t moving, which is why a chicken is so easily startled by any sudden movement. It’s also why a wily predator moves in starts-and-stops, skulking closer only when it believes the chicken is looking elsewhere.

Night Vision

The trade-off of having lots of cones for greater day vision is that chickens don’t see well after dark. Night vision relies on light receptors called rods, which function better than cones in low light. The chicken has far fewer rods than cones. The darker it gets, the less well the chicken can see.

That’s why chickens are so much easier for us humans to handle at night than during the day. It’s also why chickens are less able to watch for predators at night, and for their safety must be secured inside their coop.

Adapted from: What’s Killing My Chickens? by Gail Damerow