Ever wondered why deer freeze in front of headlights? It's not that they're admiring the lights; it's that they can't see, so they're waiting for their eyes to adjust. Unfortunately though, most of the time their eyes don't adjust quick enough. The truth of the matter is that deer have poor eyesight. They've had to learn to adapt their eyesight over the years to better identify and anticipate attacks from predators.
Here, we'll go over the strengths and weaknesses of deer vision to better understand these animals. Along the way, we will draw comparisons with human vision to better understand the differences.
An Overview of Deer's Vision
The accuracy of deer vision and their ability to detect distant objects determines how well they can anticipate the arrival of predators. Unfortunately for deer, it's not good news.
Deer have 20/100 vision. While they may sense someone or something around them, they can't focus on it until their nose is pointed up for both eyes to see. When compared to human vision, their eyesight is several times worse. That means that distant objects will appear significantly more blurry and undefined to a deer compared with a human viewing the same object.
Moreover, human eyes have UV light filters, whereas deer do not. If we see a hunter wearing a bright orange jacket and blue jeans, the jacket is going to jump right out to us. For deer, their going to notice the blue jeans and the orange is going to appear as a softer color. Humans have a “yellow” filter that partially blocks out UV light. Deer do not which is why they're so easily blinded by headlights.
Ultimately, having 20/20 vision isn't necessary for deer to seek out predators that pose a threat to them. That's because they're much better than humans at being able to detect movement. Just a tiny movement in their periphery will be enough to alert a deer of your presence.
However, it does mean that deer are not good at identifying stationary threats. They don't have the sharpness of sight necessary to detect anything that isn't moving. The upshot of this is that even a rudimentary camouflage should be effective at hiding from the view of deer.
Viewing Angle of a Deer
The viewing angle refers to one's field of view. As humans, we have a viewing angle of about 130 degrees for each eye, or about 180 in total when using both eyes together. In other words, we can only ever see about half of what's going on around us at any one time.
Deer have a whopping 300-degree field of vision when it uses both eyes, meaning they can see five-sixths of what's going on around them at any time. Naturally, this wide viewing angle makes the deer harder to creep up on, as there's essentially no single direction you could walk up to it in which does not fall at least partially within its field of view.
Night Vision Capabilities
The power of an animal's night vision is determined by how much light can be let into the pupils. In the case of humans, our comparably small pupils, meaning that we struggle to see in low light. This is why we can't see in complete darkness. Deer have horizontal pupils that are as much as three times the size of human pupils. As a result, they can let much more light in and see much better in low-light conditions.
There's another factor that makes deer well-suited to seeing in the dark: the tapetum lucidum. The tapetum lucidum is a reflective layer at the back of the retina which intensifies the light. It undoubtedly offers an advantage to sight, but it also makes deer easier to spot. Animals that possess this reflective layer are very easy to spot if you shine a light towards their eyes.
What Colors Can Deer See?
Deer color vision is limited to the short (blue or violet) and middle (green) wavelength colors. They can distinguish blue from red, but not orange from red or green from red.
Another component that assists the deer's eye to see at night is the extent to which the number of its rods exceeds its cones. Rods are the tools by which to see low light, while cones allow the detection of color. The comparatively high number of rods, and the comparatively low number of cones, means that deer cannot see the full-color spectrum.
Although the advantages may be relatively small, these color vision differences suggest that darker camouflage is likely to be more effective at avoiding detection.
Blue Light Spectrum
One portion of the color spectrum that deer are more perceptive towards is the blue light spectrum. Animals can distinguish shades of blue as much as 20 times better than humans.
Part of the reason for this spectral perception is that blue light is what the animals most commonly see around dawn and dusk when they are most vulnerable to attack by predators.
Therefore, if you're trying to get a glimpse of these animals it's important not to have any blue clothing or equipment. In addition, it's important to have softer clothing rather than clothing made of hard materials as this could allow blue light to reflect from other sources and attract the attention of the animal.
Can Deer See IR Light?
Humans are capable of seeing far into the red spectrum of light, but humans cannot see infrared light. Unlike humans, deer are not able to see very far into the red spectrum of light. However, like humans, deer cannot see infrared light at all.
The upshot of this lack of sight is that infrared cameras are a great way to track deer, as you'll be able to see the deer while they will not be able to see the IR light you're shining on them.
Can Deer See UV Light?
Humans aren't able to see UV light, in part because we have filters around our retinas designed to block it, as UV light tends to corrode retinas over time. However, humans can observe the effect of UV light as it bounces off certain types of objects and clothes.
Deer have an advantage over humans in the case of UV light. It's believed that these animals can see some way into the UV spectrum. However, the practical advantages of using this capability are limited, though it does contribute to deer's ability to see in low light.
Whether it's their lack of IR light vision or their extended capacity to detect blue light, you must get to understand how deer vision works to use it to your advantage. The way these animals see is significantly different, so unless you get to grips with how it affects their perception of their surroundings, it's going to be difficult to avoid detection while spotting deer.
While there have been recent advances in our understanding of deer's vision, scientists still don't fully know the limits of this vision, and it's not possible to know precisely how a deer sees. But, they've definitely come a long way in understanding what these unique animals can and can't see.