The Surprising Way Deer See with Ultraviolet Light

The Surprising Way Deer See with Ultraviolet Light

While writing a paper for Fungi Magazine this autumn, I stumbled into a new phenomenon in the deer woods. I was examining all of a deer's senses to determine if they were complimentary to Mycophagy (eating mushrooms), the obvious long snout and incredible sense of smell stood out as a marker for mammals that eat mushrooms. Fungi emit olfactory cues (smells) via volatile organic compounds to attract animals to eat the mushrooms as they mature, probably to ensure spore dispersal germination via scat.

What about auditory signals? Probably nothing there, although.. Fungi do communicate with sound waves and one scientist in particular is examining that.. So maybe those giant radar ears can hear em, but that's a stretch?

How about their eyes? Deer are practically blind right? I mean, they can't see you if they cant smell you and you're still.. is the consensus. Not to mention the terrible depth perception we farmers exploit by creating a two wire perimeter fence. Just in case though, I explored deer vision closer. I quickly found that they possess dichromatic vision, which means they see Blue and Yellow very well and they don't have a UV filter. WHOA, that's different then the old black, white and grey narrative I heard as a kid.

          The UV thing hit my brain hard, we know that UV or Ultra Violet light when applied to fungi, lichens and minerals reveal a hidden world of fluorescent colors. My friend Jason Asselin has a passion for fluorescent minerals including, Emberlite aka Yooperlite aka Flourescent Sodalite rocks which he hunts at night on the shores of Lake Superior. He has many Youtube videos about this and so much more, including a long history of us doing things at the old farm, foraging, and one where he gave me a solar power setup this year. He uses handheld UV flashlights made by FS Hunter, to explore beaches and unwillingly attract Mountain Lions. Fungi fluoresce under UV, deer see UV, and knowing other fungal enthusiasts have explored it (most notably Alan Rockefeller and his fb group Fluorescent Forest) I connected those dots. While looking further into the photos presented in that group, I began to see what looked like game trails that glowed blue under UV exposure. That really lit my fuse. I speculated the sign could be coming from the deer. Luckily for me, our city park has a deer pen. Yup, a couple acre enclosure at our city park to observe a herd.. welcome to yooperland! I asked Jason to borrow a light, went to the park after dark and began to shine the area. Because it's fairly well lit and it rained hard before the fresh snow had fallen, I wasn't expecting much, matter of factly I figured it wasn't gonna be a thing.

As soon as the flashlight lit up the scene, the white fur of the deer turned pearlescent blue and was reactive. Around the eyes of the deer I saw a teal blue-green-ish spot..  However, they fled as fast as they could from that light, they did not like it. So naturally I wanted to see more and walked the perimeter from the parking area, no ground sign trails, then I found a rub.. undeniably glowing like Chernobyl from 40 feet away, then I found more. They weren't everywhere, not on every tree, it was only glowing on the "hot sign". Adjacent to the park is a woods and golf course with plenty of wild deer sign which also revealed the same results. 

OK, the deer rubs glow and so does a bunch of other stuff like box elder buds and lichens, which is kinda like walking in an Avatar world when the habitat was  exposed to long wave UV. I asked a local deer processor if I could take a look at any deer he had and explained what I was seeing. He was curious too and we examined a buck, that led to discovering the tarsals fluoresced yellow, the forehead was stained blue and yellow, and the area around the eyes was also a blue-green under UV.
The sign is definitely occurring as a result of the deers glands, wow, this was amazing.

I shared this information on our Facebook page with several authorities, they confirmed the deer do see it and this is a new thing in the deer world. Since then I've been exploring it more in depth, playing with the same light I borrowed and it's been a hoot to check everything from mineral supplements and basic chemicals, clothing, tree stands, basically everything involving hunting and habitat with the light. This "experimenting" revealed some big chinks in my perceived armor very quickly, the lichens on some of the trees I had stands on were very obviously fluorescent yellow or blue-green depending on the lichen. I speculate that my silhouette obscuring those lichens would stand out to a creature that intimately knows its surroundings. Likewise, the most subtle of movements by me would reveal a hidden backlight that I never imagined giving me away. One further, the sap of many trees fluoresces too, some purple, others yellow, so my shooting lane I trimmed a month before season was highlighted with, invisible to me, neon lights like the Vegas strip.

I fully intend to explore this in more depth as time allows in the future, and several of the academics have indicated they're working this observation into their studies. 

Back to blog