Can Deer See Blaze Orange? | Dr. Karl Miller

Note: This transcript has been lightly edited from the auto-generated captions for readability — errors and hunting terms corrected, fragments smoothed — without changing what was said. Speakers: Andrew Maxwell and Jacob Myers (hosts), Dr. Karl Miller and Brian Murphy (guests).

[00:14]

Andrew: Welcome back, everybody, to another episode of The Southern Outdoorsmen Podcast. This one has been a long time coming. I'm very excited about this discussion, because today we're doing the ultimate deep dive on deer vision with probably the most qualified person on the planet to talk about it: Dr. Karl Miller. Dr. Karl, how are you doing?

Dr. Karl Miller: I'm doing great. Good to be here.

Andrew: We just recorded one a little while ago, so it's kind of weird — we might do an intro again. Anyway, Brian Murphy, how are you doing?

Brian: Doing fantastic.

Andrew: And Jacob, how are you?

Jacob: Doing great, doing great. This is an interesting conversation, something I'm very interested to get into. So, Andrew, how do you want to kick it off?

Andrew: This originally started because we were looking for biology topics to talk about. Like I was telling you earlier, Brian, there's a real hunger for it — people want to know about these things, and particularly deer vision. There are a lot of misconceptions around it. I don't think it's very well understood. And you know, while the sense of smell is obviously their first line of defense and their best line of defense—

Dr. Karl Miller: We'll discuss that.

Andrew: Oh, we're starting off with some controversy. Okay, okay.

Brian: That's the assumption, but there's some… yeah.

Dr. Karl Miller: It's wrong.

Andrew: Let's get into it. So first of all, how did you get involved with deer vision? What's the story here?

Dr. Karl Miller: At the University of Georgia Deer Lab, we've been doing research on all aspects of deer — physiology, nutrition, habitat use, movement patterns. But one thing we've always tried to keep going at all times is investigations into deer sensory perception. Trying to get inside a deer's head, because that's basically what I wanted to do — I wanted to figure out how to kill them better. So understanding how they perceive the environment is key to that.

We started off doing a lot of scent-communication research first, and we did some deer hearing, but we've always had something going on with deer vision, starting way back in the 1990s. We've had teams of graduate students — some really clever ones — and each study builds on the next. We started in 1990, and what we've learned in the last 30 years is that each time we learn something new, it makes us appreciate how much differently deer perceive their world through vision than we do. They see an entirely different landscape.

Understanding that helps you select your camo patterns, how you hunt, where you hunt, how you move in your stands, and so forth. And it's key to their survival. You mentioned smell being the key sense. Smell is key for them to find food — deer don't go through the woods with a dendrology book identifying plants; they identify what they're going to eat by smell. But as far as avoiding predators, smell comes with a hitch: if the predator is downwind or cross-wind, it's totally ineffective. The only way smell protects them is if the deer is downwind of the predator. So that's not their first line of defense — their first line of defense is their eyes.

And their eyes are keenly adapted to do two things: detect movement, and move themselves through a very complex environment at a high rate of speed — which they can do and we can't. As we go through this, you'll see how their vision is adapted for that versus ours, which is designed to do what humans do. Deer are designed to do what deer do; we're designed to do what humans do. They're not the same thing.

[04:06]

Andrew: This initially came up at the [GLN Expo?] a couple weeks ago. I was talking to you, Brian, and I said, man, I really want to do one on deer vision. And you said, funny you mention that — I know the guy.

Dr. Karl Miller: I'm just "the guy" because I had all the graduate students working under me. They're the workhorses who did the work — I just put it all together at the end. Some of the original work started back in the early 1990s, and Brian was key to coordinating one of them. It was a study where we actually got into the deer's eye to look at their ability to see different colors — whether they see black and white or actually have color vision. I'll let Brian explain some of that.

Brian: This was early in our learning curve. We had some assumptions based on how the deer's eye is structured compared to ours — pupil shape and size and so on — so we had a pretty good idea of how deer perceive the world. But there was still a lot of debate, particularly in the hunting community, over whether deer can see blaze orange. What colors could they see? Are they colorblind? From one end of the spectrum to the other.

I was working then as a wildlife research coordinator at the University of Georgia, under Dr. Miller and Dr. Larry Marchinton. We devised a vision study, but we didn't have any in-house vision experts or the equipment required. So we reached out to the two top mammalian-vision researchers in the country — one at the University of Wisconsin, one at UC Santa Barbara. That was almost 30-plus years ago now, back in 1992. The only way we could get those guys interested was to widen the scope beyond whitetails, so we ended up doing cattle, sheep, goats, fallow deer, and whitetail deer.

I remember being a young research coordinator tasked with moving a sedated steer into a laboratory, putting it into what we call a stereotaxic device to keep the head still, because we needed motionless sedated animals to put a device on the eye and introduce different wavelengths of light. We did that landmark research in '92, and the first paper came out a couple of years later. That was just the beginning — not just what colors they see, but how they perceive their environment. How can a buck run through a forest at night at full speed and not whack its head, with a set of antlers it can't even see? A deer can't see its own antlers, and it can't look in a mirror — so it has to feel its environment, at speed.

What came out of that first study was probably more questions than answers, but we determined definitively that deer are dichromats — we're trichromats. They see in two broad spectrums; we see in three. And thankfully we put the blaze-orange question to bed: deer don't have the cone photoreceptor to distinguish that color from other colors in the red-green range. It doesn't make it invisible or disappear to them — it just can't be differentiated. It's similar to protanopia in humans.

Dr. Karl Miller: It's further out the spectrum for deer than for humans. When we look at reds, as they get darker and darker they turn to black. For deer, that starts happening up in the oranges heading toward the reds — they don't see as deep into that part of the spectrum as we do.

[08:32]

Dr. Karl Miller: Let's do vision in general first — take you back to the high school science class you were sleeping through. Photons of light enter the eye, cross the cornea, go through the pupil, and hit the lens. The lens inverts the image and projects it onto the retina. On the retina we have rods and cones. Rods have a single photoreceptor, so they only see in black and white — they fire or they don't, they don't distinguish wavelengths. That's what we use in dim light, which is why everything looks grainy and colorless toward dark. Cones are what we see color with, and ours are concentrated at a central point called the fovea centralis — one little spot with an extremely high density of cones. Our cones come in three types peaking in blue, green, and red, which makes us trichromats.

Our eyes are always trying to keep whatever we're looking at pointed at that fovea, so our eyes are constantly moving. You don't look at someone's whole face — you track a point on it. That's where we get our sharp acuity and our color vision. As you move into peripheral vision you lose cones and lose color perception, and out around 120 degrees you lose peripheral vision completely. A deer's eyes are very different.

From that first study, we found deer have two cone pigments: one almost identical to our blue, and one about halfway between our red and green. So they see a yellow and a blue hue, and everything else is a combination of the two — kind of like a human with red-green colorblindness. That was the physiology. But a lot of things beyond physiology affect vision, so the next question was how well they can see those colors.

Let me add a couple more differences. Deer eyes are adapted to see very well at night; ours aren't — we're a diurnal species. Deer gather far more light for a few reasons. First, a much wider pupil: light-gathering increases with the square of the diameter, so a pupil that opens three times as wide as ours gathers about nine times the light in dim conditions.

[11:40]

Dr. Karl Miller: Second, behind their rods and cones deer have a tapetum — a reflective layer that bounces light back over the rods and cones a second time, roughly doubling light-gathering again. So you go from nine times to about eighteen. That reflective layer is what causes eyeshine — you've all seen a deer's eyes shine in your headlights.

Brian: Not that you'd be doing anything illegal like spotlighting — this is just in your headlights, on the side of the road. And deer aren't the only species with a tapetum. Lots of nocturnal-adapted species have eyeshine, because it gives them a mirror in the back of the eye to run the light through twice. We only get one pass; they get two.

Dr. Karl Miller: Think of all the nocturnal species — a cat, a dog, a whip-poor-will, an alligator — they all have a tapetum and they all eyeshine. Now here's something neat: Dr. Gino D'Angelo, during his Ph.D., dissected out the tapetum and found it doesn't cover the whole retina. It covers the top half, down to the middle, with not much in the bottom. Think about why. Light hitting the top of the eye comes from below; light hitting the bottom comes from up above — where the celestial light is, moonlight and sky glow. The deer accentuates the part that sees the dim ground below, boosting that ability.

D'Angelo also mapped the distribution of rods and cones in the back of the eye. Remember we have that one centered point? Deer don't. Their blue cones are scattered throughout the retina at fairly high density — not as dense as our fovea, more like our peripheral. But the longer-wavelength cones sit in a band across the back of the retina, not concentrated on one point.

[13:45]

Dr. Karl Miller: Now couple that with a pupil that's an oval along the horizon and a band along the retina, and think about what it does: where's a predator coming from? The horizon. Not from the ground, and eagles don't take many deer. They're most worried about a threat on the horizontal with them. That band lets them keep the whole panorama in focus, not just one point. The trade-off is that the cone density on that "visual streak" isn't as high as ours, so their acuity isn't as good — believe it or not.

Brian: Good hunting point there. If I'm watching a deer walk across a field, I have to move my head to keep it in focus. A deer watching me walk across a field can stay motionless and keep me in equal focus across that band on its retina. We have very fine acuity — we can read a newspaper, a deer couldn't — but we have to keep moving our eyes to hold something in focus. A deer can stay completely still and hold you in focus the whole way across.

Dr. Karl Miller: Easiest way to see it is a horse — similar vision. A horse standing in a pasture watches a vehicle go by and just moves its head; it never moves its eyes. The vehicle is tracking across its retina, engaging new cones as it moves, which makes movement very easy to pick up.

Andrew: Real quick — does that also mess up their depth perception?

Brian: Yeah, we're going to get to that.

Jacob: I've got a question on eye movement. We can run our eyes pretty wide, side to side. Can deer move their eyes like that, or is it mostly moving their head?

Dr. Karl Miller: They can move their eyes some. Their peripheral vision is about 310 degrees. You can sneak up directly behind a deer if you stay right behind it. But get off to the side any degree and they see you just as clearly as if they were looking straight at you — because you're still on that band.

[17:46]

Dr. Karl Miller: On depth perception: to focus at one point, our lens is elastic and flexes to set the focal length right under the fovea. Deer can't accommodate as well — they have a much firmer lens. So their depth perception on stationary objects isn't as good as ours. You've seen it: you walk into a field, see a deer at the far end, and instantly know it's a deer. The deer, though, goes "what the heck is that?" and starts the head-bob — moving side to side, trying to get you to move so it can build depth against the background. It has a hard time forming a 3D picture of something stationary.

Brian: That, plus their eyes are on the sides of their head. Anytime you move the eyes away from center, depth perception suffers. It's a prey animal — it needs 310 degrees to check every angle for predators. We're the predator, so we have a narrow field of view, but great acuity and depth perception, because that's what a predator needs to key on a target. Which is better? There's no right answer — it depends which animal you are.

Dr. Karl Miller: Deer don't have to reach down and manipulate objects. Their vision is designed to look at things remote from them, and they get their acuity through motion, not from a stationary object. That motion gives them a 3D image. It's why they can run through the woods at breakneck speed — instead of following every stick and stump, they see it play out as a panorama.

Andrew: Somebody needs to make a deer-vision simulator so we can see what that's like.

Dr. Karl Miller: You'd still be looking through human eyes to see it — unless you took your eye out and put a deer's eye in.

Andrew: I mean, it's 2024. People are doing some weird stuff these days.

Brian: I'll tell you, there are some hardcore whitetail hunters who'd have their eyes replaced given the chance.

[20:59]

Dr. Karl Miller: Here's another trade-off. Our fine acuity costs us something physiologically — processing speed. Deer don't need that sharp focus, so they can have greater processing speed. We tested it with something called the flicker fusion rate. You've seen a light that flashes faster and faster until you can't see it flashing anymore — it's still flashing, but it overwhelms your eye's ability to process it. We ran that with deer.

It turns out deer can see that flashing at much higher speeds than we can. Their processing speed is somewhere in the neighborhood of four to five times ours — meaning if there's movement, they pick it up four to five times faster. When they walk through the woods, it's like things happen to them in slow motion. That processing speed is incredible, especially in high-light situations.

And that's tied to deer "jumping the string." Everybody thinks the deer heard the bow. But the speed of sound isn't that much faster than an arrow — by the time the sound gets there, the arrow's about there too. It doesn't give them much time to duck it. What I think is happening is they can process that information so fast that they see the release — the bow moving, the bow dropping — and respond instantly, dropping to load for a bound. So I don't think bow silencers are as important as just not moving after the shot.

[23:40]

Dr. Karl Miller: That carries us to another study. We knew deer had the physiological capability to see blues, greens, and yellows — but what did they actually see? So we designed a study to let the deer tell us. A clever graduate student, Brad Cohen — now a professor at Tennessee Tech — built a deer training apparatus that works on a food reward. When the deer makes the right choice, it gets fed; wrong choice, no food. We had two bins with lights over them; when a buzzer sounded and the doors opened, if the deer fed at the lit one, it got the reward.

We started with a white light, then worked with Eveready/Energizer, who had their labs produce very specific LEDs at very specific wavelengths. We tested into the blue part of the spectrum and the red part, at different intensities and wavelengths, over and over. It worked so well we built eight units and ran trials constantly. Once the deer could no longer beat random chance, we knew they couldn't see it anymore.

Long story short, deer see into the red part of the spectrum very nearly exactly what we predicted from the physiology — similar to us, though not quite as far into the red. But very intriguingly, they see blue far more vividly than we do — an estimated 20 times as well. Because we're a long-lived species, we have filters in our eyes that block a lot of UV light; otherwise our retinas would burn out by 40 or 50. Deer don't live that long — some places a year and a half — so they don't have that filter, and that light comes right in. Their ability to see blue is incredible.

Now consider the hunter who refuses to wear this blaze orange hat but wears blue jeans to the stand.

Andrew: That being a blaze orange hat, for the audio listeners.

Brian: The concept that matters for folks confused by all this wavelength talk: if you walked under a nightclub black light with blue jeans or a white shirt, that glow — that's what we're talking about. Since the 1940s, the laundry-detergent industry has figured out how to shift the reflectance of UV light on fabric from a range we can't see into one we can. The brighteners and whiteners in your detergent reflect light differently off the fabric — but it starts in a range deer already see well and moves it into one they see even better.

Dr. Karl Miller: They see it even better.

Brian: So you're making your hunting clothes glow more and more just by washing them normally. You can take an otherwise good camo or a UV-dead product and make it "UV hot" just by washing it.

Dr. Karl Miller: A lot of fabrics have brighteners built into their dyes, and a lot of camo has it too.

[26:56]

Dr. Karl Miller: So why is blue so important to a deer? There's your quiz.

Jacob: Is it for nighttime?

Brian: What light is reflecting in those low-light hours?

Dr. Karl Miller: Pre-dawn and post-sunset, there's a lot of ambient blue out there, because blue wavelengths filter through when longer wavelengths can't. So deer rely on blues to see in low light. Ever wonder why a deer has a white tail? White reflects all available colors — and at night, that's a lot of blue. There isn't much else white out in the woods, so that tail throws a strong blue signal the herd can follow in low light. As a matter of fact, caribou can see ultraviolet even better than whitetails.

Jacob: Can you clarify — white being on the blue side of the spectrum?

Dr. Karl Miller: White is a combination of all colors. Put a white sheet on a table and it reflects every color present in the light hitting it. At night, there's a lot of blue light available, so a white object reflects a lot of blue.

Now look at camo patterns — a lot of them have white embedded, and a lot have whiteners and brighteners that push UV light back toward the blue range where deer are most sensitive. Look at that camo right before dark and even to a human it almost looks like it's glowing. Imagine what that looks like to a deer that sees blue 20 times better — you're a glowing pair of legs, or a glowing blob up in the tree. I've had deer come through where I know they didn't see me move, but they saw something up in that tree they didn't like and bolted. It was perfectly designed mimicry camo — but it was the part of the spectrum giving off reflectance.

Brian: And the harm from that blue is greatest at dawn and dusk — which is exactly when most of us hunt and when deer are most active. So it's a double-edged sword.

Andrew: Is there a UV-killing laundry detergent you can get?

Dr. Karl Miller: First, buy a detergent without the whiteners and brighteners. Then there are sprays — UV killers — that take that light and block it, undoing what the brighteners do. Or just buy a camo pattern without brighteners so you don't have to worry about it.

Brian: You can buy camo that's UV-dead if the manufacturer knows the science. But you can make it UV-hot by washing it in a UV-enhanced product. What's the most common color of laundry detergent? Blue. That's for a reason, folks. Since the '40s, the industry has learned to move reflectance from what we don't see well into what we do, to make things look brighter to us. All that does is make it up to 20 times brighter to a deer.

[33:00]

Dr. Karl Miller: Let me mention a couple more studies, some not yet published. One student, Dr. Erin Watson — now graduated from the University of Tennessee — used those same training apparatuses to look at visual acuity: how well deer can actually see. You can't get a deer to read an eye chart, so we used spectral contrast sensitivity — grid patterns at different widths and distances. As long as they could tell a grid from a solid color, we knew they could resolve at least that level of detail.

It turns out deer have a visual acuity roughly equivalent to 20/60 or 20/80 for stationary objects. They'd almost need corrective lenses to get a driver's license. People think deer have great vision — and they do, as soon as something moves. But you can stand out there dressed in pure black and stationary as a rock, and to them, you're a rock. Which tells you something about camo: a lot of patterns have fine mimicry of leaves, but deer don't see that specificity. They don't need it broken up leaf-by-leaf — they need blocking patterns that interrupt the outline of the predator. It doesn't have to match the background in design, but it has to break the outline, because what they're seeing is essentially 2D, whereas we see 3D. That's the reason behind Sitka's Optifade — the micro and macro elements that blend and distort the outline.

Andrew: When Optifade came out was the first time I heard that concept — that with a lot of other patterns, what they're really seeing is your outline, and a more pronounced outline makes your movement easier to catch. Am I tracking that right?

Dr. Karl Miller: You're both right, and there's one more aspect. What is camo supposed to do? Two things. First, keep you undetected. Second, if you are detected, keep you unidentifiable. Undetection comes down to a few things. One is movement — hard to camouflage, but breaking up your outline to match the background's blocking pattern makes movement harder to detect. The best camo for movement, though, is don't move. The other is the spectral piece: if something up there reflects very differently from the background — especially in blue — it stands out like a sore thumb. If it's blue, the deer see it vividly, and as soon as it moves against the background, it's even more obvious. Now they don't just see a blue thing up there — they see a blue human up there.

[36:53]

Dr. Karl Miller: That's the science behind the camo I'm wearing right now. Sitka just came out with one for the Southeast and Eastern U.S. called Cover, for hunting in dense-canopy situations. When we developed it, we made sure it matched the spectral signature of the background, particularly at the two peaks — the blues and the yellows — where deer are most sensitive. We tested a lot of their current patterns and a lot of prototypes, in bottomland forests, upland forests, and field edges, pre-dawn, post-dawn, and post-dusk, looking for the pattern with the minimal difference between background and camo.

The winner was one we called B20 — almost a perfect match in most situations. So it matches the background right at your peak spectral sensitivity, which means when you move, there's no color contrast to give away the movement. Layer the Optifade design on top and it also helps mask the movement of the pattern itself. That's the detection side. The identification side is built the same way — you have to break up your outline so that when a deer looks up and tries to decide whether you're a threat, it can't. If your pattern matches the background's spectrum, they really can't distinguish you from it. I'll be honest, I believe in the science here — it makes it very hard for a deer to decide what that thing in the tree is and whether it's a threat.

Andrew: I've heard guys say a solid color, like flannel, can be better than an old-school camo pattern — the idea being a solid color has no harsh lines to pick up. Assuming your UV brighteners are handled, how does an earth-tone solid color stack up against a cheaper camo pattern?

Dr. Karl Miller: With a solid color, you'll be able to see the outline of the object, which makes it easier to detect. Something blockier — large blotches of different colors that match the background — would be much better, because that obscures the outline. Identification of a predator is based on perceiving that outline; obscure it and it's harder to identify and harder to pick up movement, and it may even look like a branch moving when a squirrel jumps on it.

Brian: In a ground blind, I think black is ideal — if your background is the dark interior of the blind, black blends better than a camo pattern that doesn't fit that environment. You'll get busted quicker wearing camo in a ground blind than plain black, as long as your background is dark. And honestly, the old red-and-black plaid hunting coats of the '70s are actually decent camo based on what we know deer can see — because they can't see into those long red wavelengths, they're not seeing the red the way we do.

Brian: Another thing is the fabric itself. People say blaze orange isn't bad — and that's true, they don't see it as blaze orange. But if you're wearing a $2.99 plastic vest that reflects light off the material, not the color, that's a problem. It's like glare off a gun barrel duck hunting — it's the reflectance of light, not the color.

Dr. Karl Miller: Right — what we call surface flash matters. You get two reflectances off any fabric: the color it's not absorbing, and a flash off the surface. Materials like berbers won't flash the way nylon does. That white flash reflects all available colors, including those low-light blues — so a deer gets a blink of blue up there. Consider the fabric of the camo you buy, not just the pattern.

Andrew: Could someone check their closet right now for the bad kinds?

Dr. Karl Miller: Take it into the sunlight or shine a flashlight on it — you'll see the reflectance.

Brian: And where blaze orange is legal, it's still a big block of unbroken color. They may not see it as orange, but a big solid vest is an abnormal shape, so it's probably easier to detect. If you have the option of camo blaze orange, that's slightly better.

Jacob: Karl, can you clarify how deer perceive blaze orange and reds — since they can't see that spectrum well, what does it resemble to them?

Dr. Karl Miller: They can see in that part of the spectrum, but it's not near the peak of their sensitivity. Like I said, as we see deeper into the reds it darkens toward black; that starts happening for deer in the oranges and reds. So it's not nearly as vivid to a deer as to us.

Jacob: So it's not gray to them, just a duller color?

Dr. Karl Miller: Right. Ask someone who's red-green colorblind — those colors further out, reds and greens, are hard to distinguish. And in fall there's a lot of orange out there anyway, not much different from leaf color, so the match is relatively good. Blue doesn't match.

Brian: Back to red-green colorblindness: if you had a ripe tomato on a green vine, they couldn't tell it apart by color. Same with a blaze orange hat — hard for them to pick out of that same group of colors. And keep in mind, "color" is something we defined. It's really just reflectance of different wavelengths of light. How we perceive and name it is very different from how a deer, or any dichromat, sees the world. It's not better or worse — it's different.

Dr. Karl Miller: Let me clarify the UV point. Deer can see further into what we call ultraviolet — below about 400 nanometers, where we can't — but that does not mean they see UV as a glow, like under a black light. There aren't many black lights out in the woods. When we see blues get deeper, they go to purple, then violet, then black, and we stop seeing them well. That same thing happens further down the spectrum for deer — as they go into the ultraviolet, it gets less and less vivid. They can still see color there, but it doesn't glow. The glow happens at their peak sensitivity, back in the blues — which is what the brighteners exploit by moving UV into that visible blue range.

[46:50]

Andrew: Might be a dumb question, but how does their depth perception and movement detection affect hunting off the ground — say brushing into a natural blind instead of a pop-up? Is there a right or wrong way to brush yourself in — front cover, back cover, all of the above?

Dr. Karl Miller: With a natural blind, the biggest challenge is concealing motion, not just concealment. Being behind something is a lot easier than concealing in front of something, so you want more cover in front of you. But you also don't want distinct movement against the background — if the whole thing moves as one, it's harder for them to distinguish.

Brian: Remember, a deer's eye is built specifically to detect predators on the horizon — which is exactly where a ground blind sits. In a tree stand you have an advantage: they don't normally look up for predators. They will — we've all been busted in trees — but it's not their natural inclination, because most threats come from the ground. So ground hunters have to be even more sensitive to movement. You can get away with more in a tree, particularly if a deer is distracted. Same with jumping the string: a wound-up deer is much more likely to react and bolt than a calm one. A lot of it is watching the deer's behavior and moving at the right time.

Dr. Karl Miller: That's critical. There's a ton of information coming through a deer's eyes, and it can only process so much at once — but it can focus that processing. Walking along scanning, it's just looking for movement. But the moment it detects something, it can throw all its brainpower at analyzing that one thing and ignore the rest. So once you're busted, it can really lock on — which is why the priority is not getting busted in the first place.

Brian: So they can get distracted like humans, and forget about things for a moment — which is what we all look for. You're waiting with a deer in bow range for that magic moment to draw, and finally something else grabs its attention and it locks onto that. For that millisecond, that's your draw opportunity. But a deer that's on edge and knows something's there? Try to draw and nine times out of ten you're busted.

Brian: Better to wait it out — even let them walk out to maximum bow range — than to draw on one that's wired. If they're wired, every sense is on full alert: 310 degrees keeping you in focus, ears wide open and rotating — every alarm bell going.

Dr. Karl Miller: Another thing with tree-stand hunting is the angle. If you're 20–25 feet up and the deer is right under you, there's no way it sees you. But out at 30 yards, you get back into that sweet spot reflecting off the band on its retina.

Jacob: That goes back to what older guys did in the '70s and '80s before scent control was a thing — climb as physically high as you can, especially gun hunting, and hope your scent drifts past or above them, especially with thermals. You get a vantage that way.

Dr. Karl Miller: That's the big thing. There's so much wind movement in a forest — upper and downward thermals, morning and evening eddies — that it's pretty hard to mask your scent if the wind's moving at all. The best thing is to be downwind. Just hunt smart.

Andrew: Another question — for breaking up your outline with a ghillie or leaf suit, how important is the camo pattern specifically, if the material itself is disrupting your outline?

Dr. Karl Miller: With a ghillie you have no outline anymore. A ghillie suit is great. The only issue is if it's solid black, you'll be able to pick up the motion of that solid color, versus something with a lot more edge to it. Just make sure it doesn't have any difference in spectral reflectance either. So it's the shape, but also the spectral reflectance — but a ghillie is a great camo.

Andrew: We're going to use them this year. Fired up.

[52:45]

Jacob: Any other studies you or anyone else are looking into on deer vision?

Dr. Karl Miller: Just a hint of some data: another student, Dr. Blaise Newman, recently finished work at UGA looking at deer movement through their environment based on the spectral availability at different times of day. A forest, an open area, and a patchy area can each have very different availability across the spectrum. She found deer tended to avoid moving through parts of the environment with a lot of spectral reflectance, particularly in the blue — I'd have to re-read it to be sure. The bottom line is their movement reflects light availability in the environment. Obviously food and predator avoidance are the top two drivers, but the light spectrum may play a role too. This was done in Florida, so it has to be repeated — I'm just throwing it out as a hint.

Jacob: When it comes to eye injuries — a one-eyed buck — would much change? That 310 degrees would get cut down. Any diseases that affect the eyes?

Dr. Karl Miller: Not really. A deer that loses an eye loses some binocular vision, which helps depth perception — but they don't have a fovea centralis like we do, so their depth perception isn't great to begin with. With one eye, a deer just turns its head to compensate. I don't think a one-eyed deer would have much of a problem.

Brian: There are examples of blind deer that have survived. A one-eyed deer would survive at nearly equal rates — more subject to ambush from its blind side, but overall a fairly minor challenge. Like one-eyed humans, they just move their head more; as long as one eye is good, you're still seeing the world.

Brian: One unique thing about deer vision that's kind of cool — and it doesn't affect their vision — I've only personally seen and photographed one: a doe with amber-colored eyes. Deer normally have dark eyes. One in tens of thousands has this beautiful amber, chestnut-colored eye, and they look like devils — really different. If you see one, count yourself lucky. Rare, but cool.

Dr. Karl Miller: Here's another cool one. You know how a deer's pupil is a slit along the horizon? What happens when it puts its head down to feed? They have a process — cyclovergence — where as the head lowers, the eye rotates to stay level. It turns in the head, so the deer maintains that horizon. Even with its head down, it's not looking at the ground, it's looking out.

Andrew: That is fascinating. I thought you were going to say they see up and down better — that's why I get busted drawing on them all the time.

[58:01]

Jacob: Anything else we're missing on deer vision — any other data points you found interesting?

Dr. Karl Miller: There's still so much we don't know, and we can't literally get inside a deer's head to know exactly what it sees. Everything I've told you is our best interpretation of the data. There's a lot more to learn about what part of the spectrum they see and how they use their vision for everything they do.

Andrew: You said you got into this to get better at hunting. Other than helping design the Sitka camo, how has this information changed your own hunting on a personal level?

Dr. Karl Miller: From the deer's side, other than "don't wear blues" — I used to wear blue jeans to the stand religiously — watch your movements. But one of the biggest things I've learned isn't even about vision. It's about how you enter and leave a stand, what you do in the stand, and every single interaction you have with a deer — because every interaction teaches that deer something.

That's important for people who use the same stands repeatedly. Every behavior a deer has is a learned behavior. They're not naturally avoiding humans until they're taught to, by experience. The more experience you give them, the smarter you make your deer, and the more they'll avoid certain areas.

Jacob: Has there been research on a deer's memory or mental capacity — conditioning, classical conditioning?

Brian: I can point to a study at Chesapeake Farms in Maryland — and it's been done many times, including in Georgia — looking at deer use of landscapes with permanent stands that get hunted frequently. They absolutely avoid them at a statistically significant rate. The Georgia study, done just south of here, looked at overhunted food plots with box stands versus those that weren't, and daytime use of the overhunted plots just plummeted during the season, while the unhunted ones stayed active. It got so bad that if you were hunting one of those overhunted box stands, you could literally throw a dart on the map anywhere on the property and have a higher chance of killing a deer than at that stand.

Dr. Karl Miller: And that's not the only study to show it. One of the first was at Westervelt in Alabama — the heat-map study. We did one in West Central Georgia where, during the breeding season, bucks absolutely avoided feeders. When baiting became legal, everybody worried all the big bucks would get killed. But those bucks got big by getting wise — they avoided the bait stations, or checked them from well downwind to see if does had gone in. On that lightly hunted property, the worst place to sit would have been over a feeder or a food plot.

Brian: How many of us have seen it — a novice who knows nothing about the property goes and sits somewhere random in the woods and kills a big buck?

Andrew: Or they're trying to gar-hole some kid at the club — stick him in the spot where nobody ever sees anything.

Brian: Right behind camp. Think about what that's telling a deer.

[01:02:43]

Dr. Karl Miller: Here's a question I get a lot: what color light should I use walking into my stand? I don't think it matters. Deer aren't inherently afraid of light — how many get hit by vehicles with huge lights coming at them? They don't run from street lights or lightning bugs. I'd use a dimmer light walking in, and if you're really worried, use red, since they see blue well. But a deer has no concept that a light moving through the woods has a 180-pound human with a weapon behind it — all they see is the light, same as they only see the light on the road, not the ton of metal behind it. Unless you teach them otherwise — with noise, a human cadence — the light isn't the important thing. Being quiet and scent-free walking in is.

Brian: I'm convinced that if you condition a deer that "light equals the smell of a human," you can create a learned behavior. So I prefer not to use a light if I can help it. Maybe I'm overcautious, but I don't want to condition a deer to anything I don't have to.

Dr. Karl Miller: I used to coon hunt a lot in college, out at night carrying a bright light. Sometimes I'd walk right up behind a deer moving through the woods, and it had no care in the world that I was behind it.

Jacob: On conditioning deer to avoid permanent stands — what advice do you have for private-land guys, whether it's a club, a lease, or land they own, if deer start avoiding the permanent stands?

Brian: The Westervelt study I mentioned created heat maps of hunter activity and overlaid deer movement and harvest — the brightest areas of human activity were some of the lowest areas of harvest. We do the same things over and over, and eventually they stop working. But the flip-side myth — that you can never kill a big deer from a box stand on a food plot — is absolutely false. If you hunt those food sources strategically, at the right times, on the right wind, and are careful, you can kill big deer from permanent stands all the time. You just can't hunt them over and over and condition deer that it's a problem area.

That's hard in a hunt-club situation unless you have some limiting factor — a stand only gets hunted once a week or every two weeks — to prevent constant pounding. The other issue is driving noisy four-wheelers right up to within 100 yards of the stand. And there's a study out of Mississippi that looked at the classic Friday–Saturday–Sunday scenario: guys pile in Friday, run around on ATVs checking feeders and cameras, hunt Saturday and Sunday, and go home. They found it takes on average 48-plus hours for deer to return to normal behavior after that weekend disturbance. Statistically, your best chance of killing a deer on historically weekend-hunted property is Wednesday and Thursday — after the previous Sunday's disturbance fades (about three days) and before the Friday crowd arrives.

Dr. Karl Miller: Consider the food plot and conditions too. If the wind's not right, don't hunt it — only hunt it where deer approach from upwind. Think about your access to and from the stand, especially leaving in the evening; have a way to get down and out of sight before deer bust you. Your stands don't have to be in the middle of the food plot — tuck them into a corner so you can slip away without disturbing deer in the field.

Brian: Or better yet, have someone in a vehicle drive in and bump the deer off the plot for you — better than crawling out and letting every deer watch you walk across the field to your car. The worst thing I see over and over is people putting box stands right in the middle of a food plot. Most of these are evening hunts, and you'll usually have deer in the field when you leave — so you're almost guaranteeing you pattern those deer against you, just by how you set up.

Jacob: It's like guys on Andrew's club.

Andrew: You think they drive 100 yards? How about seven yards?

Jacob: Literally park the truck or four-wheeler and step out onto the box stand and climb in. And some of them leave that last 15 minutes of light — almost like they're scared of the dark — and drive back to camp. Then they wonder why they don't kill anything on the food plots. Plus the plots are tiny, quarter-acre or less.

We brought this up with Bronson Strickland when we interviewed him. The people he'd seen have the most success killing mature bucks on food plots were doing one of two things: hunting them very sparingly, at a specific timed point, and then leaving them alone — or setting up to gun-hunt from way back off the plot, up a road bed in the woods, cutting lanes to shoot 100-plus yards into the field, so they could slip out without being seen or heard.

Brian: Most of the stands on my hunting property use both of those strategies. You have to shoot through the forest to get into the field, which gives us a great back door, and we hunt them very sparingly. We kill a lot of fully mature bucks on those food plots — but we wouldn't if we hunted them like a traditional hunt club: wrong spot, over-hunted, deer busting you constantly. Those two simple things make permanent stands almost un-patternable, because you're not giving deer a consistent enough pattern to key on.

[01:10:39]

Jacob: We've got a few minutes left — Karl, could you talk a little about deer hearing? We mentioned it before recording.

Dr. Karl Miller: There have been relatively few studies, but two good ones. Dr. Gino D'Angelo, during his master's here, used an electrophysiological method — monitoring a sedated deer's brainwaves in response to different sounds played into the ear — to map which frequencies they hear best and their range. That gave us an idea of their physiological capability. Combine that with a behavioral study done at the University of Toledo by the father-son team Heffner and Heffner, who trained deer to respond to sounds for a reward — like Pavlov's dog — and built a behavioral audiogram. Both matched well. It turns out deer hearing isn't that different from ours.

Brian: With some exceptions.

Dr. Karl Miller: They hear a little better in the higher frequencies, but they can't hear those vehicle deer whistles — the ones people put on trucks years ago. Even if the whistle made a sound, deer couldn't hear it. Their hearing is about the same range and acuity as ours, which surprises people, because everybody assumes "that deer heard me, its hearing must be great." The real difference is a deer knows what it's supposed to hear in the woods — and what's not supposed to be there. We hear a noise on the stand and turn to look, "what's that, a squirrel?" A deer hears a squirrel running through the leaves and doesn't even lift its head. We're in their bedroom; they're not in ours. Drop a nickel on your kitchen floor and you'd know exactly what it was, because you're used to those sounds. We don't live in the woods 24/7 like a deer.

Brian: They can directionalize much better, though — gather more sound and localize it better than we can. One big takeaway is the difference between low- and high-frequency sound. Low-frequency sounds — fog horns, train whistles — are denser and travel farther. High-frequency sounds — metal, an arrow ticking a rest — come out fast but die quickly, like a .22 versus a shotgun blast. So the sounds to avoid are the unnatural, high-frequency ones: the tinks and dings that aren't normal woods sounds. Most natural woods sounds are more tonal.

Dr. Karl Miller: On directionality: deer have large external ears — pinnae — that do two things. They funnel sound in, which actually increases hearing ability beyond what we measured right at the ear, and they help localize the source, because you localize by the difference in a sound arriving at one ear versus the other. But there's a caveat: when a deer turns its ears toward something, it hears less from behind. So it gives up something for that directionality, which is why you'll see a deer work one ear, then the other, gathering information from different directions.

Brian: And while their range and intensity aren't that different from ours, they're more in tune with their environment. Like a blind person — their hearing isn't better than mine, but it's finely adapted from necessity, so they hear things I don't. Early in the season I don't hear as well as I do later. As the season progresses and I train myself to separate normal from abnormal sounds — I'll sit with my eyes shut and try to identify every sound — I become a better predator. My hearing sharpens, my ability to pick up movement improves. A deer does this every day of its life; we only do it seasonally. Our noses are a joke compared to a deer's, but our eyes and ears can definitely improve over a season if you train them. It's a trained skill.

Andrew: You mentioned deer know what they're supposed to hear. One thing I've done for about 10 years now: if I just can't be quiet walking into my stand, I'll yelp like a turkey every once in a while — and man, does it work. I think it's because everything eats a turkey, they're skittish, and they walk on two feet like we do, so if a deer hears a turkey sound, it's like, okay. That's worked well, especially bushwhacking into a new area on public land where you just can't be quiet.

Dr. Karl Miller: Another thing you can do is pay attention to what a deer's cadence sounds like versus a human's. They can identify a potential predator, or other deer, by the sound of their footsteps too.

Jacob: Interesting. We're running short on time.

Brian: One point about grunt calls while we're on hearing. The two studies Karl referenced, plus one from Texas A&M, all came up with the same results on deer hearing — but one tested the frequency of the average grunt call and found it sits right in the peak sensitivity of a whitetail. A grunt is a low-frequency sound, so it travels farther in the environment and lands right in their peak hearing range. So grunt calls are very effective — you don't have to be as loud as you think. Just know your call is going farther than you probably realize.

Jacob: Yeah, I love calling deer — you don't have to be as loud as you'd think.

Dr. Karl Miller: One more thing right in the peak of a deer's hearing: the brushing of fabric against a tree, or your fabric against itself. So choose your fabric accordingly — if it's really noisy, that's right in their sweet spot. Years ago I worked with Sitka and we redesigned their [acoustic?] system based on deer hearing, and reduced the engagement distance — how far a deer could hear the fabric before it attenuated — by about 20 or 30 yards. Minimizing that sound is critical, especially in the part of the deer's range where hearing is best.

Brian: The human voice matters too, particularly male voices. You've all experienced it — a woman or child with a lighter, squeakier voice doesn't travel far, but a deeper or louder voice carries.

Jacob: It carries way further. I've been in the woods so many times hearing two guys talking, like they're right in my back pocket, and they're 250 yards away just talking — not even screaming — but they've got that deep voice.

Dr. Karl Miller: Which brings us back to those vehicle deer whistles. They're supposed to make an ultra-high-frequency sound, but the thing we're talking about is attenuation — very high frequencies attenuate extremely fast. For a whistle to project loud enough in front of a vehicle at 60 miles an hour, it would have to be so loud it would shatter every window in the car. And most work passively, with air producing the sound out the back, so even if a deer heard it, it'd be on the side of the road going, "what the heck was that?"

Brian: And they tested them — a lot of the early models didn't even make a sound. They're above our hearing, so we couldn't tell without testing. It's a perfect sales pitch: the deer can't hear it, you can't hear it, but trust us, it works. You can't prove it. Some people buy anything on hope.

[01:22:10]

Jacob: We're at time, gentlemen. I greatly appreciate you both joining us. Karl, one last thing — if listeners want to find some of these published studies, where do they go?

Dr. Karl Miller: Most of it's in the scientific literature, so go to Google Scholar and search under each topic — "deer vision," or under my name — and those papers will show up. They're written as scientific studies, not adapted for hunter applicability, so you'll have to infer that yourself. But this is a great resource — podcasts like this get the information we generate out to the public so they can actually use what we're finding.

Brian: Another good place where a lot of this has been written up in a more popular, semi-scientific form is the National Deer Association website. Any printed material they have cataloged on these subjects could still be available. Just search Dr. Miller's name with some of these topics — there have been articles over the years in various popular and semi-scientific magazines, and you can find it if you look hard enough.

Jacob: Fantastic. Thank you all again for joining us. Listeners, thank you for listening. Viewers, thank you for watching. We'll catch you on the next episode of The Southern Outdoorsmen Podcast. Remember, guys — y'all stay Southern.