|
|
Post by Surroundx on Sept 18, 2014 22:23:35 GMT 10
I was reading a bit of the old literature on the thylacine the last few days and noticed that Hans Naarding says that the eyeshine colour of the thylacine he saw in March 1982 was "pale yellow". From memory I can recall two reports from pre-1936 Tasmania describing their eyeshine colour as green (I think Owen, 2003 may have been one of the sources, quoting an old-timer). While mainland thylacines have been described by Sid Slee and somebody else as having blue eyeshine (see YouTube video below). I need to track down exact references for all this, so does anybody know of any? How much colour variation do individuals within a population (normally) exhibit, with the exception of albinos complicating matters? I was reading a forum post from another forum and one poster said that research had shown that thylacines actually had blue eyeshine and not yellow/green. Anybody know what research is being referred to here?
As Paddle (2000) states, and many of us know only too well, much of the literature on the thylacine is inconsistent to say the least. Eyeshine colour being the area I'm particularly interested in at the moment, so hoping to make some headway.
Incidentally, what do questers make of Naarding's sighting/report?
|
|
|
|
Post by dennisw on Sept 19, 2014 0:20:17 GMT 10
Eye-shine in most animals is often red due to reflection from blood vessels behind the eye, "red-eye" is a common problem in flash photography but is less likely if the subject is not looking directly at the camera. The eye is a spherical object and spheres can reflect the entire spectrum (raindrops produce rainbows by refracting the light passing through them; Sir Isaac Newton wrote the first and IMHO still the best definitive paper on refraction in rain), the colour of eye-shine may often be more relevant to angles rather than species.
|
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Sept 19, 2014 8:08:59 GMT 10
I cant add anything to Thylacine eyeshine but I can vouch for vocalisation.
I once visited a hollow tree with Nev Smart. The tree stunk and was a known Thyla den. Juveniles were seen to run to it on a prior occasion, following a cough from the edge of the scrub.
I tapped on the tree and called, "Anyone home".
A voice answered, "GRRRRRRRRR". This was for real and not a fantasy.
BC
|
|
|
|
Post by molloch on Sept 19, 2014 8:50:05 GMT 10
Eye shine is not related to the reflection from blood vessels, it is due to an adaptation in the back of the eye in nocturnal vertebrates that refocusses light back through the retina to improve vision at night. Red-Eye in humans is actually something different - we have no nocturnal adaptation - and is to do with the reflection from blood vessels. It is more pronounced in blue eyes, and can occur in animals with blue eye mutations.
Eye shine colour can vary within a species due to the size and shape of the eye, and can even vary depending on your angle relative to the light source and the animal's eye.
Your best bet would be to look at closely related species. I think quoll eye shine is white, and Devil eye shine might be white too, but I can't find anything concrete on this. Maybe Dr Tom could do some field testing for us?
|
|
|
|
Post by molloch on Sept 19, 2014 8:59:33 GMT 10
|
|
|
|
Post by muffin aka set24 on Sept 19, 2014 14:52:58 GMT 10
I was reading a bit of the old literature on the thylacine the last few days and noticed that Hans Naarding says that the eyeshine colour of the thylacine he saw in March 1982 was "pale yellow". From memory I can recall two reports from pre-1936 Tasmania describing their eyeshine colour as green (I think Owen, 2003 may have been one of the sources, quoting an old-timer). While mainland thylacines have been described by Sid Slee and somebody else as having blue eyeshine (see YouTube video below). I need to track down exact references for all this, so does anybody know of any? How much colour variation do individuals within a population (normally) exhibit, with the exception of albinos complicating matters? I was reading a forum post from another forum and one poster said that research had shown that thylacines actually had blue eyeshine and not yellow/green. Anybody know what research is being referred to here? As Paddle (2000) states, and many of us know only too well, much of the literature on the thylacine is inconsistent to say the least. Eyeshine colour being the area I'm particularly interested in at the moment, so hoping to make some headway. Incidentally, what do questers make of Naarding's sighting/report? There is some conjecture on the actual eyeshine colour of the thylacine. to what i have read the colour being a yellow to blue. hav'nt heard of green. there was a sighting, descibed on the tas tiger sightings cd, of a man and his wife, who were out spotlighting, and came across this "animal", presumably they thought it was a thylacine, and consequently the husband yelled out 'tiger shoot' the wife presumbly had the gun, and described the animal having blue eyes (eyeshine). Hans naarding report is regarded as a credible sighting, although we have only his word for it,(as with other sightings), hans said it was raining heavily, would have been extremely dark, sighted the animal at some distance?, was caught in his torch light, was able to watch the animal for a time ? was not able to reach his camera in time,until the animal diasppeared into bush. could probably be interpreted as a "normal" sighting. animal was seen then diappeared, not enough time to get a picture. |
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Sept 19, 2014 19:32:30 GMT 10
Eye shine is not related to the reflection from blood vessels, it is due to an adaptation in the back of the eye in nocturnal vertebrates that refocusses light back through the retina to improve vision at night. Red-Eye in humans is actually something different - we have no nocturnal adaptation - and is to do with the reflection from blood vessels. It is more pronounced in blue eyes, and can occur in animals with blue eye mutations. Eye shine colour can vary within a species due to the size and shape of the eye, and can even vary depending on your angle relative to the light source and the animal's eye. Your best bet would be to look at closely related species. I think quoll eye shine is white, and Devil eye shine might be white too, but I can't find anything concrete on this. Maybe Dr Tom could do some field testing for us? Hi Molloch, I admit I have no knowledge of the mechanism by which the eyes reflect colour. So no idea who is right or wrong regarding the Thylacine. All I can say is that the little quolls that run around my place every night reflect the outside lights as a pale yellow/off white kind of shine. Definitely not orange or green or blue. Funnily enough I can't recall what colour the Devil's eyes reflect...I must check next time I see one. (Digressing here...) Sadly, it seems the facial tumour disease has reached our area, so they may begin to suffer. I may be crazy, but I thought I might build an enclosure and apply for a Permit to keep a disease-free pair. Anyone know my chances of success (with bueaucracy, I mean...) |
|
Deleted
Deleted Member
Posts: 0
|
Post by Deleted on Sept 19, 2014 19:37:57 GMT 10
About Naarding's report.
I have read it in detail.
Apparently it took place at about 2 AM.
Although it was raining and (obviously) dark, he had a spotlight and the animal was not distant at all.
His camera was in the glovebox and he was in the rear of his vehicle.
He (correctly) assumed the animal would move off if the light moved off it, so he gathered as much detail as he could before trying to reach his camera. As soon as the spotlight wobbled (as he moved) the animal was gone.
He was a trained observer of wildlife (he was at the location on a bird survey) and so his report must carry some weight.
|
|
|
|
Post by Surroundx on Sept 19, 2014 21:39:21 GMT 10
About Naarding's report. I have read it in detail. Apparently it took place at about 2 AM. Although it was raining and (obviously) dark, he had a spotlight and the animal was not distant at all. His camera was in the glovebox and he was in the rear of his vehicle. He (correctly) assumed the animal would move off if the light moved off it, so he gathered as much detail as he could before trying to reach his camera. As soon as the spotlight wobbled (as he moved) the animal was gone. He was a trained observer of wildlife (he was at the location on a bird survey) and so his report must carry some weight. Here is the relevant extract from Naarding's report to the TNPWS, cited in Andy Park's 1986 article Tasmanian Tiger: Extinct or Merely Elusive?"I had gone to sleep in the back of my vehicle which was parked at a road junction in a remote forested area in the north-west of the State. It was raining heavily. At 2 a.m. I awoke and, out of habit, scanned the surrounds with a spotlight. As I swept the light-beam around, it came to rest on a large thylacine, standing side-on some six to seven metres distant. My camera bag was out of immediate reach so I decided to examine the animal carefully before risking movement. It was an adult male in excellent condition with 12 black stripes on a sandy coat. Eye reflection was pale yellow. It moved only once, opening its jaws and showing its teeth. After several minutes of observation I attempted to reach my camera bag but in doing so I disturbed the animal and it moved away into the undergrowth. Leaving the vehicle and moving to where the animal disappeared, I noted a strong scent. Despite an intensive search no further trace of the animal could be found." (cited in Park, 1986: 76) I'm intrigued by your statement that the animal would not have moved off while the spotlight was on it. I had assumed that nothing of the sort would occur, quite the opposite really. Is this reaction to light sources widespread in the animal kingdom, or at least vertebrates? Thanks. |
|
|
|
Post by saggitarius on Sept 21, 2014 21:22:22 GMT 10
Possums react exactly the same. Put a light on them and they freeze. It is interesting to have a mother ringtail and a couple of young ones all freeze as they are picked up using an overhead wire to get from point A to B. If you keep the light on them they don't move, but if you move the light for even a second they scamper along the wire so fast. it is hard to believe.
I have also had foxes freeze when hit by a spotlight.
|
|
|
|
Post by Surroundx on Sept 22, 2014 0:27:22 GMT 10
Possums react exactly the same. Put a light on them and they freeze. It is interesting to have a mother ringtail and a couple of young ones all freeze as they are picked up using an overhead wire to get from point A to B. If you keep the light on them they don't move, but if you move the light for even a second they scamper along the wire so fast. it is hard to believe. I have also had foxes freeze when hit by a spotlight. Thanks for the info, Saggitarius! I wonder what would cause this behaviour? I can't imagine that there would be any analogue in nature to a spotlight etc. being shone on an animal, so it would have to be a manifestation of something else. |
|
|
|
Post by saggitarius on Sept 22, 2014 9:51:39 GMT 10
It might be as simple as a preservation reflex. Here's something different - possibly a threat - I'll freeze while I see what is happening. Then once the light moves or flickers, the possible threat becomes something and the animal flees.
Just my tuppence worth!
|
|
|
|
Post by molloch on Sept 22, 2014 11:22:05 GMT 10
I'd agree with Sagittarius that this is a fear/freeze/flight response, but these are also crepuscular/nocturnal animals with a highly reflective layer of cells on the back of their eye. A strong light shining right into their eyes when their pupils are fully dilated would be blinding, as well.
|
|
|
|
Post by youcantry on Oct 1, 2014 14:05:22 GMT 10
My 2 cents: I investigated this question of eyeshine colour too and my present understanding is that the thylacine had/has gold/yellow eyeshine.
I don't think looking at "closely related species" is going to be any help. In truth, "relationship" is something we humans impose across species based on (originally) physical and (then later) genetic similarities. Neither of these would be definitive for determining eyeshine colour in my opinion. I am sure eyeshine is a physical property and when it comes to diffraction of light I get the impression that the tiniest little microphysical change can make a world of difference.
Consider this - a single butterfly might have a dozen brilliant and different colours on its wings. Yet the wings are consistently covered in scales. What creates the different colours? I am sure it will be microscopic differences in structure, possibly even chemical differences. If a single butterfly wing with scales that are far more similar than different can produce a huge array of colours, then surely it doesn't matter how closely related (or not) we think two species are - their eyeshine can be vastly different.
(And yet within a species there appears to be consistency).
Regarding blue as an option for the thylacine - I can only imagine this being consistent with yellow if the shades of both were close to white. What I mean is - solid yellow like the text on this page, and solid blue like the other text on this page, are vastly different. However if the predominant feature of thylacine eyeshine is a bright whiteness, then I can imagine the tint being slightly off toward yellow or blue and that not seeming impossible within a single species.
Heck, humans have all different kinds of iris colour, so why shouldn't other species produce slightly different eyeshine colours?
|
|
Thylacoleo Gal
Administrator 
Thylacoleo Gal
The Singularity is near.
Posts: 3,689 
|
Post by Thylacoleo Gal on Oct 2, 2014 7:37:47 GMT 10
I have always understood that all young mammals show blue eyeshine - apparently the 'baby blue' pigment is universal. But now I'm not so sure about marsupials: come to think of it, I can't recall any examples of blue in a marsup. Anyone able to cast light (pun!) on the question? There's a young fox on the index page of www.thylacoleo.com where you can clearly see the 'baby blue' eye colour: just refresh the screen to show it before the main rollover. The second thing that's sort of related to this topic is that I have read that some (not all) human females are 'tetrachromats'. Normally, humans are 'trichromats' and so can see a full colour spectrum of red-green-blue. It's the so-called 'cone cells' in the retina that respond to colour. Apparently, tetrachromatic women have an extra, mutant version of the long-wave, red-responsive type. This confers a finer ability to discriminate colours. Presumably, such women would see a world richer in red-pink-orange-yellow hues that the rest of us do. Being inherited, it's an ability you would have since birth, but I can't say I myself have ever been aware of any reported difference between the colours I perceive and what other people say they see. Guess I must be a plain ordinary trichromat. |
|
|
|
Post by dennisw on Oct 2, 2014 8:33:22 GMT 10
It is impossible to say that the way you see colour is the same way that others perceive those same colours, you may well be seeing colours better than others but as you have always seen them in that manner you would be unaware of the advantage you have and just assume that was "normal".
|
|
