Eye Shine and Owlet Nightjars

To: Mona Loofs Samorzewski <>, Birding Aus <>
Subject: Eye Shine and Owlet Nightjars
From: Denise Goodfellow <>
Date: Mon, 18 Nov 2013 20:33:14 +0930
And wolf spiders' eyes (for that's what you're seeing), appear to change
colour as you approach them!

Denise Lawungkurr Goodfellow
PO Box 71,  Darwin River,
NT 0841
043 8650 835

On 18/11/13 6:24 PM, "Mona Loofs Samorzewski" <>

> Thanks Andrew for that excellent explanation.
> Along the same vein, I have walked around the bush at Howard Springs near
> Darwin at night with a head torch on, and seen many many reflections coming
> from the ground from spiders eyes. And they were blue! A friend with a
> hand-held torch wasn't seeing them at all until he put my head torch on. And
> then we realised how many spiders we were walking on...
> Mona
> On 18/11/2013, at 4:54 PM, Andrew Hobbs wrote:
>> There are two types of 'eye shine'.
>> As Chris said it is partly simple physics. By the nature of the eye and its
>> focus on the back of the eye when light is shone into it there is a
>> reflection from the back of the eye. As is the case with anything being
>> illuminated, at least some of the light is reflected back along the same path
>> and will appear to cause the eye to 'shine' (compared to the rather
>> non-reflective coat of hair, feathers etc).
>> But there is another factor.  Some animals (including some birds such as
>> owls) which are active at night, have a layer at the back of the eye called a
>> 'Tapetum Lucidum'.  This layer contains mineral crystals which have the
>> property of reflecting almost all the incident light back along the same path
>> as the incident light. (Look up 'Corner reflector' on Wikipedia) This layer
>> is behind the layer of light sensitive cells, doubling the sensitivity of the
>> eye. (The cells have two chances of capturing photons; coming and going).
>> When you shine a light into an animal or bird with these eyes they really do
>> appear to shine very brightly. However the reflection is not perfect and some
>> light is reflected back somewhat 'off axis'. In this case, because the
>> reflection is so strong, you can still see a reflection even if your eyes are
>> well off the same axis as the torch beam.
>> In contrast, in animals (and birds) without a Tapetum Lucidum, the light is
>> reflected of the Fundus at the back of the eye.  This is not a good reflector
>> but some does get reflected back along the axis.  Because the reflection is
>> so much weaker your eyes need to be much closer to the axis of the torch beam
>> to see the effect.
>> The colour of the eye reflection from the Tapetum Lucidum depends upon the
>> properties of the crystals in the layer.  It can vary more or less across the
>> full visible spectrum.  However in animals without that layer the reflection
>> is always red.  The red colour is mainly due to the haemoglobin in the blood
>> vessels at the back of the eye. (This is the basis for the red eye effect in
>> people. We don't have a Tapetum Lucidum.)
>> Andrew
>> On 18/11/2013 12:18 PM, Chris Corben wrote:
>>> Roger
>>> It's very simple physics. Almost anything looks brightest when the light
>>> source is close to your eyes. But in addition, a bird's eye is pretty much
>>> retro-reflective. That is, the light reflected by it mostly goes back along
>>> the path it came from. If you think about it, you are looking at the inside
>>> of a sphere, so wherever the light comes from, it is reflected back in the
>>> reverse direction. The same principle is used to make road markings shine
>>> brightly at night. The paint on a road is filled with tiny glass spheres, so
>>> that from whatever direction the light arrives, some portion of it is
>>> retro-reflected. Since the headlights of a car are not too far off the line
>>> of your sight, a lot of that light comes back to your eyes, and the markings
>>> look bright. If the paint was just plain gloss paint, it would be much more
>>> reflective, but nearly all the light from the headlights would be reflected
>>> away from the driver, and the paint would look essentially black. As does
>>> smooth ice, 
>  and for the same reason.
>>> Owlet Nightjars eyes are not nearly so bright as White-throated Nightjar's
>>> eyes. But even a White-throated can be seen at much greater distance with a
>>> light which is close to your eyes. It makes such a difference, that you can
>>> wear a headlamp and see the eyes of things like owls at reasonable distance
>>> even though the headlamp is not very bright. A side benefit of this is that
>>> the lower light levels will scare the bird a lot less, so you can actually
>>> gain by having a lower intensity light if it is close to your eyes. A
>>> headlamp is perfect for that!
>>> Incidentally, if you know to look for it, you can see eye-shine of animals
>>> in all sorts of unexpected ways. A classic case is to get to a place where
>>> there are frogs on the surface of the water. If you get the sun straight
>>> behind you (eg in early morning or late afternoon), you will be able to see
>>> their eye-shines surprisingly well, especially if you use binoculars.
>>> Using binoculars with a headlamp is a great way to find all sorts of
>>> creatures at night. Frogs, snakes, geckoes, spiders, small mammals and even
>>> bats in the right situations. Just use your binoculars to look at the spot
>>> of light from the headlamp.
>>> Cheers, Chris.
>>> On 11/17/2013 08:39 PM, Roger McNeill wrote:
>>>> A few weeks ago Gus McNab was over and we were discussing spotlighting and
>>>> I mentioned how I have a good population of Owlet Nightjars on our block
>>>> but I never see them at night because their eyes don't eyeshine, despite
>>>> wandering the woods after hours.
>>>>  He told me (politely) how wrong I was and the issue was that I was not
>>>> holding the torch in the right place to see it.  What I needed to do was
>>>> walk around like a unicorn with the torch beam emenenting from between my
>>>> eyes.  I (polietly) said that is faseniting, thinking that this was surely
>>>> some ploy to make me look like an idiot...not that help is required...and
>>>> thinking how that could possibly be true?
>>>>  Last night, I had a visiting bird-o who wanted to see Nightjars and other
>>>> things so we decided to wander the tracks and see what we could find.
>>>> First try was for White-throated Nightjars...two birds pearched up for us,
>>>> brilliant eyeshine.  A koala started calling back at the house so we
>>>> wandered back, yep bright eye shine...we then decided to walk down to
>>>> "owlet-nightjar grove" and I had three birds respond and two come in, one
>>>> quite close.  I put the torch on the bird and as expected no-eyeshine...but
>>>> then I tried Gus' recomendation and move the torch between my eyes and wow,
>>>> its eyes shown back bright red like a Christmas tree.  Amazing! Gus you
>>>> were right, but I have no idea what the explanitaion was or why this is the
>>>> case!  Thanks for the tip...wanted to share publically.
>>>> Cheers,
>>>> Roger
>>>>  Roger McNeill
>>>> Samford Valley, SEQ
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>> -- 
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>> Andrew Hobbs
>> ***********************************************************
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