Can Owls See in the Dark? How Owl Eyes Really Work

How owl eyes are built

Owl eyes are huge for the size of the bird. In large owls such as the great horned owl, the eyes are roughly as big as a human’s, even though the owl weighs only about 0.9–2.5 kg (2–5.5 lb). They take up much of the skull, so much that the two eyes almost touch inside the head.

The eyes are not ball-shaped like ours. They are long and tube-shaped, with a large cornea and lens at the front. This shape lets owls have big eyes without needing an enormous round eyeball, and the large front opening gathers plenty of light, a bit like the wide lens of a camera made for low light.

The tube shape is held in place by a ring of small bony plates called the sclerotic ring. As a result, owl eyes are fixed in their sockets. An owl cannot roll its eyes to look sideways the way we can, so it has to turn its head instead. Owls can rotate their heads up to about 270 degrees, as explained in can owls turn their heads 360 degrees?.

Rods, cones and seeing in dim light

The retina, the light-sensitive layer at the back of the eye, contains two main kinds of cells. Rods work in dim light and detect brightness, while cones work in bright light and detect color. Owl retinas are packed with rods and have relatively few cones.

Along with the large pupil and lens, this rod-rich retina makes owl eyes very sensitive. An owl’s pupils can open very wide at night, letting in as much light as possible, and close down in bright light.

Owls have forward-facing eyes, which give them a wide area of binocular vision, where the views of the two eyes overlap. This helps them judge distance accurately when they strike at prey. Their overall field of view is narrower than that of many birds with eyes on the sides of the head, such as pigeons.

How good is owl night vision really?

Owl night vision is excellent, but less magical than many people believe. In the 1970s British zoologist Graham Martin measured the sensitivity of the tawny owl to dim light in laboratory experiments. He found that the tawny owl’s eyes were only about two to three times more sensitive than human eyes, not the hundred-fold difference sometimes claimed.

That is still a real advantage, and owls are much better than us at seeing fine detail in dim light. But it means that on a cloudy, moonless night in a dense wood, an owl’s eyes may be close to their limit. Martin and other researchers argue that owls depend heavily on hearing and on knowing every perch and flight path in their territory, which may be one reason many owls stay in the same territory for life.

Owls are also far-sighted. They cannot focus well on objects very close to the face. Stiff, hair-like feathers around the bill help them feel prey and food at close range.

Hearing: the owl’s secret weapon

When light runs out, owls hunt by sound. Many owls have a large facial disc, a ring of stiff feathers that works like a satellite dish, collecting sound and funneling it toward the ears hidden at the sides of the head.

In several species, including the barn owl and the tawny owl, the ear openings are placed asymmetrically, with one higher than the other. A sound reaches the two ears at slightly different times and loudness, which lets the owl pinpoint where it comes from both left to right and up and down.

In famous experiments published in 1971, American biologist Roger Payne showed that barn owls could catch mice in a completely dark room, guided only by the rustling sounds the mice made. When a rustling object was pulled across the floor, the owls struck at the source of the sound, showing that they were aiming by ear. This is the clearest proof that owls do not need light to hunt.

Silent flight helps too

Hearing prey would be harder if the owl’s own wings were noisy. Owl flight feathers have soft, comb-like front edges and fringed back edges, and the surface of the feathers is velvety. Together these break up the turbulence that causes whooshing sounds, so most owls fly almost silently. This lets them hear their prey as they approach and keeps the prey from hearing them. The details are covered in how do owls fly silently?.

Do all owls rely on night vision?

Not all owls hunt in the dark. Some species, such as the northern hawk owl, the snowy owl and the burrowing owl, are often active in daylight and hunt mainly by sight, as described in are all owls nocturnal?. Strictly nocturnal owls, such as the tawny owl, depend more on hearing.

Myths about owl eyes

Myth: owls can see in pitch darkness. No animal can see without light. Owls use excellent low-light vision when there is some light, and their hearing when there is none.

Myth: owls are blind by day. Owls see well in daylight and can shrink their pupils to protect their eyes from bright sun.

Fact: owls cannot move their eyes. Their tube-shaped eyes are fixed in place by bony rings, so they turn their flexible necks instead.