bobthebirder's picture

Reflections in water

More of a physical observation than a natural one but this is something I would love to have explained to me.

On several occasions I have been surprised to see that when a kingfisher flies away from me low over the water its reflection is not orange but blue. Yesterday I found a kingfisher perched at Radipole Lake as I walked to work in Weymouth and made a particular point of watching it carefully as it flew away. At first, when the bird was flying directly opposite me I could see the reflection of its orange underparts, as you would expect. Then as it flew further away the reflection changed to blue until I was seeing a perfect image in the water of its bright blue back. The bird was flying very close to the water on a perfectly calm morning with the sun behind me low in the sky.

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Carstairs's picture

blue

Doppler effect, they do fly fast. ;-)

TBH I have noticed this myself and don't have a clue why its so. Only seems to be with kingfishers. Maybe it's just down to the vividness (is that a real word or did I make it up?) of the blue?

Tarby's picture

Upon reflection

My guess would be that there is;
1) more light falling onto the upper plumage, and
2) the blue plumage is glossier, so able to reflect more light.

As the bird moves away the weaker orange light is lost, leaving the blue.

Go placidly...

Refugee's picture

Physics teacher

We need a physics teacher or an optician. When being shown light going through a prism the blue/purple are at the opposite end to the red/orange. The images of the two colors may be either merging or separating while being reflected as the angle changes.

Refugee

David Jardine's picture

Underwing reflection?

I wonder if the reflection is being influenced by the underwing colour, which is part blue (primaries and secondaries) and part orange (underwing coverts)?

RoyW's picture

Optical illusion?

I wondered if sometimes this isn't actually true at all, and is a case of the brain fooling us into seeing what we subconciously believe we should be seeing?
We all know that Kingfishers are bright blue, therefore we know that their reflection should be bright blue (false logic of course because they are obviously also orange, and a variety of other colours), but our brains don't always show us what is really there!

In most cases I would think that this effect is due to a combination of the angle of our viewpoint, the direction of the light, and the degree to which the body of the kingfisher may be tilted, and we are genuinely seeing a reflection of the upperparts even though it appears that only the underparts should be reflected.
See these photos as examples:
http://www.rspb.org.uk/community/cfs-filesystemfile.ashx/__key/community...
http://www.flickr.com/photos/15383380@N06/6151134006/in/photostream/

Refugee's picture

Human eye

The human eye may take a different time to respond to different colors of light. A test can be done with a few electronic components to be found in experiment kits that are some times sold in gadget shops with blue and orange LEDs added in order to prove this.

Refugee

Ray Turner's picture

Angle of Reflection

The laws of reflection are as follows:
1. The incident ray, the reflected ray and the normal to the reflection surface at the point of the incidence lie in the same plane.
2. The angle which the incident ray makes with the normal is equal to the angle which the reflected ray makes to the same normal.
3. The reflected ray and the incident ray are on the opposite sides of the normal.

http://en.wikipedia.org/wiki/Angle_of_reflection

Instinctively we think of the reflection being directly under the originating object but in fact it is some way between us and the object. The above laws (mainly law 2) combine to mean this point of reflection is where the angle of the light from the object is the same when it bounces up to our eyes (foreshortening tends to push this point closer to the object than it actually is). What we see then is an image of the object as though we were looking from that reflecting point. The difference in angle between the direct light waves and the reflected ones is not great so the reflected image is not wildly different from the one we see directly.

Using Roy’s first example we can see a very slight difference between the direct image and the reflected one. Look closely and compare the leading edges of the wings particularly how much of the right underwing is visible and how much undertail. This is consistent with a closer lower viewpoint.

Ray

Ray

Refugee's picture

Speed

the Kingfishers i have seen fly so fast and low over the water that the response time of the human eye is very likely to come into play. I think it is the most likely cause of this.

Refugee

Dluogs's picture

Angle of Reflection

Thank you, Ray (and Roy for the pictures)! I've really enjoyed following the thinking about this puzzle - and am now happy to read your post which suddenly makes perfect sense. But thank you for waiting a while - it's been fun to explore the alternatives.

Sarah

bobthebirder's picture

kingfisher conundrum

Well, I think I understand it now, but I'm not sure I can put it into words! Basically, at any appreciable distance away from the observer, the reflected image will be the same as the object observed. As in Roy's linked photos. I was expecting to see the kingfisher's underparts because I was thinking from the kingfisher's perspective - the bird, if it looked down, would of course see its orange underparts reflected in the water. And that's what I was thinking would always be reflected. But for that to be true, I would have to be riding on the back of the kingfisher!

Now to test that last hypothesis...

Bob Ford

jmc942's picture

colour.

I have read all the posts here and find them a very interesting read. I dont know if im correct but what is the colour underneaththe top layer of plumage? obviously the top layer is orange but have they got blue under feathers or down? what I mean is, as the bird flies the plumage lifts up and out displaying a differnt colour underneath so as not to scare the fish. and the orange breast is just a display? but i have never been that close to a kingfisher to know so i may be talking rubbish haha

Jamie

bobthebirder's picture

plumage

As far as I know, the kingfisher is blue on top, orange underneath. The feathers are likely to be a bit darker underneath but this would not show in flight as they will be lying flat against the body.

Bob Ford

Wildlife Ranger's picture

Ventral Colour kingfishers

Hi A very Interesting Thread

The answer may lie on this link

http://www.bbc.co.uk/nature/life/Common_Kingfisher

It may well be an evolutionary characteristic selected over thousands of years - from the Fish perspective the Irredescence might mean a fast bird approaching minimises movement by the bird in so far as possible using this simple but effective adaption which must have some bearing when the refractive index of the two mediums air and water as to what potentailly a fish might see.

WLR