Regarding eye-shine and nocturnal versus diurnal…Cathemeral actually.

Friday, July 27th, 2012

Regarding eye-shine and nocturnal versus diurnal…Cathemeral actually.

I had two restorative surgeries about a year and half ago, most people do not know that I went blind about two and a half years ago and was partially blind even after my surgeries and I actually asked my doctor about this during one of my follow-up appointments. I have one of those coming up this Friday. Dr. Nash is one of the top surgeons in the Pacific Northwest. What really is aggravating is that I still have problems with one eye (right) and I am still partially blind in that eye and will probably be that way for life because of water behind my retina, which made me a case study discussed across the United States in an attempt by Dr. Nash to find an answer. Why in the world can I just be mundane? Anyway, enough about that sad affair.

I asked Dr. Nash about the eye luminescence and he never heard of it either, to which I am not entirely surprised because it is possible to not have knowledge about something despite holding a specialty in that area. Still, the eye is a remarkable organ and I will tell you what I do know. We know that eye shine (tapetum lucidum which means bright tapestry) is actually a result of the tapetum which is behind the retina.

Let us break it down a little more. There are two types of receptor cells, gees now I am teaching one of my biological psychology classes, anyway, there are rods and cones. The cones are our color receptors and they are configured in trios of arrays of red, green, and blue.

Note from Dr. Anna Nekaris: “Remember though that we are trichromats and that amongst the haplorhines (if yeti/bigfoot is an ape/primate) any cryptohominin is likely to be a haplorhine and trichromacy has evolved three times with different patterns of rods and cones.”

The rods are actually light receptors and help us, and other animals, to see in low light conditions. We have more rods than cones, just like many other animals have fewer cones than we do which makes them less receptive to colors, but also more adaptive to dark conditions than humans – this is also why humans lose some color sensitivity at night. Think about it, in the low (blue) light of the moon all colors look the same, it is only when we illuminate an area with brighter (white) light do we begin to make out colors, some more so than others. Behind the array of both types of receptor cells, which constitutes the entire retina, is the tapetum which is a mirror like membrane that actually reflects light back through the eye which helps some animals see better at night.

Another thing I learned from my research is that the tapetum color varies in different species which is the reason for the different eye-shine colors in different species.

Note from Dr. Anna Nekaris: “This is definitely true – this is how I I.D. the different animals in the forest – it also has to do with crystalisation of the retina (according to my obsessed colleague on this subject).”

Also, different animals have different intensity of eye shine because some animals have a greater concentration of rods and fewer cones. Even the angle of the reflective light can change the color of the eye-shine because in some species the tapetum has different colors as well, so where the angle of light it reflecting, that is the color that presents reflectively.

Some animals have specific, or typical, reflective eye-shine color. If I recall correctly, alligators have a typical reddish-orange versus yellows and greens of other animals. So let us recap. Some animals have a greater potential for reflective eye-shine than others, I think cats are pretty high, especially wild cats like mountain lions and bobcats. Very little lumens can generate a reflective eye-shine because of the mirror quality of the tapetum it takes very little light to accomplish this, again, the more sensitive, or greater necessity of the species to function affectively in darkness, the more this will likely occur in specific species.

Note from Dr. Anna Nekaris: “It is also eye size – the tarsier for example has no tapetum but it can see in the dark. And monkeys and humans have no tapetum but we have (including tarsiers) what we call eye GLARE – when you look at them with the torch (flashlight) AT EYE LEVEL you still get bounce off the retinal crystals – usually dull but you can still see them glowing.”

A couple of other notes I have found in my research over the last year, humans do not have a tapetum, yet we are still capable of reflective eye-shine, mainly red; by the way, most primates do not have a tapetum lucidum. This is because the actual retina is reflecting the light back through the capillaries in the retina creating a red reflective eye shine. It is actually possible to know what kind of animal, within reason, is looking at you by the eye shine color (Note from Dr. Anna Nekaris: “Hehe, I had not even read this yet – but yes – see above”). Now I am not a specialist on that so I cannot rattle off which animals have which colors, and I may be incorrect in trying to recall some of them so please forgive me if I do not remember correctly. Birds and rodents tend to be reddish-orange. Cats can vary something like green to yellow (gold) and dogs too and raccoons. Frogs I think are green and bears are red. Frogs are green, alligators reddish-yellow, cows and horse tend to be blue, and if you see a white sparkly eye-shine those are spiders and fish. I hope I remembered all of that correctly.

There are also some night birds and fish that seem to have glowing eyes (reflective eye-shine) that have the same situation, no tapetum. Some of the preliminary findings I have read discuss that these species have a variation called Tapeta Lucida, and again is not a true glow but a light reflection based on cell structure and oils.

Note from Dr. Anna Nekaris: “Amazing – yes – except if you are me and you live with a red light so you do not disturb them – but this is exactly it – except for nocturnal primates which glow brilliant red! Also nocturnal birds are bright red.”

Please understand that I am not a biologist, I am a psychology professor and I teach biological psychology classes which is physiology regarding the brain and the peripheral nervous system which is why I know about receptor cells (our senses) and how they function in providing stimuli. But I am not a specialist in this area regarding animal physiology and I am just providing generalities in this regard. There are more nuances than what I am communicating here. Still, I have yet to find anything that discusses actual “glowing eyes”, that is that eyes emit light which is different from reflective eye-shine. There are some fish, insects, and plants that do have a natural iridescent glow, but those are not related to the eyes.

Again, I am still in the process of learning more about this, but have failed, so far, to see anything even with all of my available resources, to find anything on iridescent (light emitting) eyes.

So how does this affect our understanding of the Bigfoot phenomenon? In most legitimate reports where eye-shine or glowing eyes are given as part of the description, we find that the standard eye color is a variation of red. We know that large primates do not have tapetum lucidum and that eye-shine comes out as red-eye because of the reflection of light back through the capillaries in the retina as stated above.

There are some primates that do have tapetum lucidum, or some variant, such as the lemur and Loris’ but interestingly enough, they are nocturnal. Dr. Anna Nekaris is a specialist in nocturnal primates and a member of Team Bigfootology, so I will ask her about this directly and get her expert opinion.

Anyway, so there are two possibilities here; the first is that Bigfoot is nocturnal (awake during the night) and despite the fact that it is a very large, the largest primate, it may have a tapetum lucidum as part of the eye physiology.

Note from Dr. Anna Nekaris: “This is possible but it would be very strange. We do have evolutionary reversals like the tarsier – if a creature for some reason re-adapted for a nocturnal existence it would be more likely to have LARGER eyes that brought in more light than to re-evolve a tapetum. So if we think that the cryptohominins have any relationship to apes/humans/etc…it would be very, very unlikely to have a tapetum.”

The second, and one I think more likely, is that Bigfoot is more closely related to humans because of its ability to breed with humans, it is diurnal (awake during the day), something I have been preaching for a while, and they do not have a tapetum lucidum as part of their retina physiology. Yet, they have very large ocular cavities as we have seen from Khwit’s excavated skull, the son of Zana. This means that the retina area is also far larger and gives a larger reflective area, the fact that most legitimate reports are red indicates the probability that the reflective light is indeed picking up the red from retina capillary.

Note from Dr. Anna Nekaris: “A. It could make sense that over time if, for example, with competition from other large hominins Bigfoot sought to live more in the dark, individuals with better capabilities to see in the dark were selected for so in general they could have larger eyes. They definitely would have eye glare – NO DOUBT – because all monkeys do – but to see it you would need to torch (flashlight) at eyelevel. It would be no wonder if people would see this for example from a car as most people see the tapetum in the car as the car beams are often at eye level.”

Nocturnal versus Diurnal…Cathemeral actually.

Now some of you have heard me speak about the fact that I believe Bigfoot is actually diurnal and not nocturnal, but I will repeat myself here for the benefit of clarifying the above point. First, most reports of sightings and interaction occur during the day. If they were nocturnal they would be sleeping in their nests or shelters and not interacting with humans or in a position to provide an opportunity for humans to see them.

So how do I explain why they have activity at night and I explain that by giving basic human behavior. Humans are diurnal with the exception of skewed circadian-rhythms. Still when the sun goes down do we go right to bed? Not at all. In the northern areas of their primary locality humans would sleep for up to 12 plus hours per day in the winter time because of the length of darkness. So we do not go to bed when the sun goes down. We stay up and interact with our families, friends, entertainment, what have you. When we go to bed if we hear something unusual around the house we get up and investigate what is happening. The same applies to the Bigfoot population. Their home, however, is the forest and when we invade the forest to camp, they are going to check in and watch us, investigate the noise around their home. Make sense?

I proposed this theory to Dr. Jeff Meldrum and he stated that it was viable because some primate species that are diurnal have indeed adapted to a nocturnal life in order to survive, humans included, just ask someone who works the swing shift or graveyard shift (a shift in the circadian-rhythm).

Note from Dr. Anna Nekaris: “I was going to suggest though that they could also be cathemeral or crepuscular. If they do have large eyes they could be active when the moon is bright (lunar philic) or they could be active at dawn and dusk (when many sightings take place too – e.g. I was about to leave the forest to go home when I saw…). So there is normally less competition from humans at those times or time to come into conflict with them, but visibility is better…and the full moon – we always say it is like someone turned on a tube light out there.”

All of this information is part of a series of species profile articles that I am writing for, but I thought I would share because I was asked and there are some sensible answers to this phenomenon, so I hope this helps. The reality is that we do not know for sure. What we do at Bigfootology is look at evidence through the prism of known species to determine what is viable and what is not viable, and to make sense of behavior and other aspects (including physiology and morphology) of the Bigfoot phenomenon that we glean from the narrative evidence of then eyewitness report.

Rhettman A. Mullis, Jr., MS, MHP

Note: I want to thank Team Bigfootology and Oxford Professor and Primatology, Dr. Anna Nekaris for her valuable insight and affirmation of what I wrote in the article above. In conducting further research into this matter and taking into account her mentioning of Cathemeral, I have evolved my conclusion that Bigfoots are Cathemeral not strictly nocturnal or diurnal.

Cathemeral: Applied to an activity pattern in which an animal is neither pre-scriptively nocturnal, nor diurnal, nor crepuscular, but irregularly active at any time of night or day, according to prevailing circumstances. Read more…by going to the source. (Source:

Crepuscular: Of, relating to, or resembling twilight, active in the twilight <crepuscular animals>. Read more…by going to the source. (Source:

Trichromats have all the three types of functioning cones and should see all the different shades of colors. Normal trichromats are people with normal color vision. Read more…by going to the source. (Source:

Haplorhines are monkeys and apes.  Read more…by going to the source. (Source:

Category : Bigfootology Field Report

You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.

Comments are closed.