Owls are notoriously known for their eyes due to their strikingly impressive size in comparison to their head/body (they take up half the space within the owl’s skull and account for around 5% of the owl’s body weight!). If asked to name 5 of an owl’s key physical features I can bet that their eyes would make the list. In this article, we will be taking a closer look into the fascinating abilities of an owl’s eyes and answering the key question… How good is an owl’s eyesight?
Owls have very good eyesight, which can be up to 100 times more superior than a human’s. The primary reason for this is their incredible ability to control the amount of light that enters their eyes, allowing them to see clearly in any and all light conditions, specifically at night.
Owls can see with only one-tenth to one-one hundredth the amount of light that humans need to see clearly. This is because owls have the ability to re-emit light back onto the retina to provide a second opportunity for light to enter the eye and enhance visual sensitivity at low light levels. Due to this, and the multitude of reasons highlighted in the below article we can conclude that ultimately, owls vision can be 100 times better than ours.
First of all, let’s start with looking into the structure of an owls eyes (check out my other article here about owls eyes, which explores why owls bob and rotate their head). See below image of the cross section of the anatomy of an owl’s eye:
Let’s quickly run through what each part of the eyes anatomy is for, and what this does for the owl:
Optic nerve – Like all living beings with an optic nerve, this carries messages from the retina to the brain.
Pecten – A non-sensory, pigmented structure found in birds and reptiles which nourishes and controls the pH of the vitreous body (The vitreous body is ‘empty space’ within the eye which gives the eye its shape. It is the space between the lens and the retina and is filled with a clear jelly).
Scleral Bone/Ring – The bony structure which surrounds and supports the eyeball, this helps to keep the vision as sharp as possible for hunting.
Iris – This is the part of the eye that holds colour and it contains the pupil within the center. The Iris controls how much light is allowed into the eye to control the size of the pupil.
Cornea – The transparent part of the eye that covers the iris and the pupil and helps your eye to focus light to be able to see clearer.
Retina – A light-sensitive layer of nerve tissues located at the back of the eye which omit electric signals of images and send them through the optic nerve to the brain.
So, now we have clarified what each part of the eye does, we can explain how these individual parts combine to assist the owl with its lifestyle needs.
Most species of owls are active during the night or in the early hours before the sun has risen and therefore their eyes need to be able to process light effectively in low light conditions. Therefore, to do this the iris enlarges the pupil so that more light can pass through the lens and onto the large retina allowing great visual quality even in dim to almost no light. Please note – owls cannot see in pitch black as they do need some light source present but this light source can be very close to pitch black. In fact, an owls night vision is anywhere from 35 – 100 times better than humans.
It is also important to note that the owl’s pupils can easily adjust the same way to bright lights in the day time, as some owls are not nocturnal. Some species of owl can actually see better than humans in the daytime. So as you can see, the control of light entering the eyes plays a huge role in how good an owls eyesight is. Since they have large eyes, they have a large surface area, meaning there is space for lots of light to enter and then be controlled to ensure that owls can adapt to any level of light and see incredibly well. Each pupil can dilate independent of the other meaning they can control the light level of each individual eye slightly differently to better focus the sight.
Sometimes, animals that have impressive eye sight, especially in low light conditions can appear as if they have glow in the dark eyes when a light is flashed at them (for example, think of a cat caught in headlights, leading to the invention of cats eyes on roads) they appear to glow and owls eyes are much the same. This is caused by something called ‘tapetum lucidum’ which means reflective layers that sit behind the retina, which re-emit the light back onto the retina to sort of double the chance of light hitting the eyes and therefore their ability to see in the dark is doubled.
I have written a previous article about whether owls blink here which explains in more detail that owls actually have 3 eyelids – a normal upper and lower lid, where the upper closes when the owl blinks and then the lower closes when the owl sleeps. Then the remaining third eyelid is called a Nictitating Membrane which is a thin eyelid which shuts diagonally and cleans and protects the owls eye surface. Since their eyes are much larger than many animals, they need a little more protection from the elements so this extra lid works a treat!
The sclerotic ring structure around the owl’s eyes limits the movement of the owls eyeball and therefore improves the owls focus. We are all aware of the fun fact that owls can rotate their heads 270 degrees but this isn’t just for fun, this is a vital skill needed because their eyes do not move within their sockets (binocular vision). Their eyeball shape is tubular rather than round and therefore to look in different directions an owl must move their head rather than their eyes. This means that once an owl is still and focusing on its prey, their focus will not stray – This aids with hunting because the prey will not be lost. In fact, owl’s eyes are the most forward facing of any bird which means they have the best depth perception. I explain further what depth perception means for owls here.
Some may say that a minor downfall within owls sight is that they are quite limited in the colour they can see and therefore most of their life is in monochrome! This is because the rod-shaped cells found within the owl’s retina are very sensitive to light and movement but do not process colour well. Cone cells found within the retina help the eyes to react to colour but owls unfortunately have limited cone cells within their retina. Short-Eared owls are more active during the day so they have better colour vision than most other species of owl. This is because colour is much more useful for sight during the day than at night. Colour is rarely a vital aspect when it comes to night vision.
Therefore owls have brilliant eyesight, unmatched in many ways but not without its weaknesses (if you would even call them this). Their inability to see much colour and their inability to roll their eyes in their sockets doesn’t impact the owl negatively as these abilities are exchanged for much superior abilities which aid in their successful hunting abilities and specific lifestyle needs. Colour is not vital for most species of owl due to their nocturnal nature as colour doesn’t play much of a role in eyesight when you are in dark conditions. Likewise, an owls inability to move their eyes within their sockets is exchanged for their ability to focus on their pray with impressive binocular vision.
In conclusion, I hope this article has helped you understand the anatomy of owls eyes and understand why this means owls have incredible eye sight. As mentioned in my intro, an owls eyes are a key physical feature for their identification and I hope you find it fascinating understanding how they work and ultimately how they benefit an owl and its lifestyle. This is only a basic beginners explanation but it introduces you to the topic and I can confirm there is so much more to learn about the owls eyes, which I aim to delve into much more on this site – so stay tuned!
