Nature News: Sparking Curiosity About What Doe-Eyed Creatures See

published on and in The Portsmouth Herald, the York Weekly, Fosters Daily Democrat etc.

White-tailed doe gazing at a drone in Addison ME photo by Everett Grant

My classes have been remote this fall. This is a hard thing for a science teacher-I like my classes to be messy, to get outside and explore, to get to know my students face to face, not through the lens of a computer’s camera.  I try to bridge the electronic gap by sharing stories about things I have recently seen, hoping to make some kind of connection, spark some curiosity.  

Last week I was telling my biology class about some people out walking in Kennebunk Plains who were wearing blaze orange vests that had a black camo pattern.  I said I thought this was weird–if you’re wearing bright orange, why the need to camouflage?  I had a few hunters in the class who explained about it being deer season and the necessity of wearing blaze, which led us off path and down the rabbit hole following the question, what exactly do deer see?  Can they see that bright orange vest?  If so, then the camo pattern is pointless.  But, if they can’t see bright orange, then the camo makes sense.  This didn’t fit in with my daily curriculum plan, but it is biology, so we did some research.

I had always thought that deer were color blind, and so thought I knew the answer to the question I had posed-what do deer see?  Turns out I only knew part of the story.  

If you have ever looked at the face of a white-tailed deer you have noticed its prominent  brown eyes.  Doe-eyed means (according to the Oxford Dictionary) “having large, gentle, dark eyes.” Deer have large eyes because, as a prey species, they need to be able to see as much of their environment as possible so that they can flee at the slightest hint of danger.  Their eyes are placed to the sides of their heads allowing them to see in a wide arc without moving their heads – a helpful adaptation for survival.  Deer have the eye placement of prey, humans, with our forward-facing, binocular vision that allows for better depth perception have the eyes of a predator.  Deer can both graze and watch for predators at the same time, we humans would need to post a guard.

But, what can deer see? Can they see that blaze orange vest? 

Like many nocturnal and crepuscular (active at dawn and dusk) animals, deer have a much higher density of rods in their retinas compared with cones.  Rods are light receptors (more than 1000 times more sensitive to light than cones).  Because deer are most active at dawn and dusk they need to be as sensitive to light as possible, packing lots of rods into their retinas helps them see very well in the dark.  Cones, on the other hand, are active at higher light levels, they detect color and are responsible for high resolution vision.  According to Penn State’s Jeannine Fleegle,“Even though deer have less than half the number of cones in the eye as humans, deer can still distinguish among different colors. During low-light conditions, deer are likely more sensitive to the blue to blue-green portion of the spectrum (due to the high rod density). Studies indicate that deer are less sensitive to light of long wavelengths (orange and red) and rely upon their perception of only 2 colors – yellow and blue.” (from “The Eyes Have It” published in the Deer-Forest Blog  2015). 

This means that red, orange and green all look the same to a deer-meaning that blaze orange vest might very well blend into the surrounding greenery.  But to truly blend in you have to be careful what material your vest is made out of and what you wash it with.  Deer lack a UV filter in their eye-they can see further into the UV spectrum than we can (we have a UV filter in our lens, presumably to help protect our eyes from damaging UV radiation-an issue when you are most active in daylight).  Shiny materials and cloth washed with various detergents and brightening agents all emit more radiation in the bluer/UV part of the spectrum and will stand out to a deer in the same way that blaze orange vest stands out to us. 

Sparking curiosity?

What we learned in class is just the tip of the iceberg in the study of deer vision. Other aspects of deer eyes come into play-their horizontal pupils for one.  Why do some animals have horizontal pupils? Great question! Sadly the quarter is over and I won’t get to pursue this in class, but I’m hoping that, having been introduced to the interesting differences between human and deer vision, my students might want to investigate this question all on their own.