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UltravioletPhotography

Platycercus eximius [Eastern rosella]


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Wow! Alex, thank you for these super cool bird photos.

 

It is very educational to see an avian UV-signature.

Of course, we still must wonder what such UV patterning means to the birds themselves? :D

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This appears to be two simultaneous exposures in different bands. How was this achieved? You could easily assemble a GBU image from these frames.
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Yes, I know birds can see in UV. But does this help them distinguish their species from others? The UV-signature appears to be the same for the male and female so it does not appear to help them distinguish gender. Perhaps UV-signatures also act as a camouflage against predators. Just wondering about it all.
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Andy Perrin

Hm. I assume that, like the bees, the birds see visible as well as UV. Given that UV is such a small percentage of sunlight, I wonder if they even see much difference. The UV patterning is white in areas that are visible-white and pretty uniformly dark in areas that are visible-colored. So if you overlaid the UV on the visible and made it only a small percent of the total, the visible would simply overwhelm the UV for them. Or so I would think!

 

Edit: This article had some interesting things to say.

It is now known that many birds, probably most, have some degree of UV vision, which they use to find both food and partners. The berries that some feed on have a UV bloom, and European kestrels can track their vole prey from the UV reflecting off the voles’ urine trails. The plumage (or parts of it) in hummingbirds, European starlings, American goldfinches, and blue grosbeaks reflects UV light, often more markedly in males than females. In certain species, like the blue grosbeak, the degree of UV reflectance may also reflect male quality, though females don’t currently use this aspect of plumage to discriminate between potential partners.

 

Maybe some good suggestions for further bird species to photograph in there, Alex!

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Yes, I know birds can see in UV. But does this help them distinguish their species from others? The UV-signature appears to be the same for the male and female so it does not appear to help them distinguish gender. Perhaps UV-signatures also act as a camouflage against predators. Just wondering about it all.

 

Does it have to have a purpose?

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Such stuff is rarely purposeless. But sometimes it take us humans a while to understand it. For example, fluorescent sea creatures. One use of the fluorescence by some of these guys is to camouflage their dorsal side by brightening it up so they cannot be seen by predators from underneath when viewed against the brighter sea surface. This permits the animal to come to the surface to do whatever it is they do there. (I forgot that part of the vid I recently watched. Sorry!) In other fluorescent sea animals, the fluorescence confuses predators or acts as mate or friend signaling.

 

So I tend to think that there is some benefit to those birds which have UV vision and UV "markings". Of course, a reflected UV photograph doesn't really represent how they see one another. But it does tell us that these birds see each other differently than the way we see them. (Well that was obvious. But I'm trying.)

 

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These Rosella birds are just the most beautiful things! I've been fascinated by them since you posted.

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In this case there seems to be a correlation with the visual reflected color's placement in the spectrum and the UV reflectance. Could it simply be that greenish-bluish-white feathers reflect UV better than yellow-red-white? (or may be not - the tail feathers do not fit with this).

 

On the sensory side there are examples of mammals that are able to respond to UV light. My physiology colleagues in Tromsø where I worked before moving to Alaska have studied this in Reindeer. They think that UV perception becomes important at weak light at dusk and low light in the high arctic, when UV wavelength dominate the spectrum more than in bright sunlight. A few links, resulting from the search "Stokkan reindeer UV"

 

http://jeb.biologist...ent/214/12/2014

http://arctic.journa...ticle/view/4381

https://www.ncbi.nlm...les/PMC4232876/

For those very interested his homepage with more references can be found here: https://uit.no/om/en...ension_id=88165

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There is a paradox to purpose and purposelessness. Not everything results in 'purpose'.

Can there be purpose without purposelessness.

Exploration and experimentation are both.

 

Not everything that may have a reason in one spectrum has a reason in another, not to say that it doesn't also, but not always.

 

This paradox of reason has come up before:

http://www.ultraviol...uorescent-frog/

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Andy Perrin

In this case there seems to be a correlation with the visual reflected color's placement in the spectrum and the UV reflectance. Could it simply be that greenish-bluish-white feathers reflect UV better than yellow-red-white? (or may be not - the tail feathers do not fit with this).

 

Not sure about those tail feathers, but for the rest, it may be that if the colors are produced by iridescence in visible light, the same physical structures will give a dark UV outcome because the spacing of the repeated structures that give the visible colors is not correct for UV. That is, to pick a simpler example, if you have a diffraction grating with a spacing between the lines that puts the visible light at the correct angle, the UV will be at the wrong angle because the wavelength is halved.

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Andy, is there any evidence that UV-pattern is caused by iridescence? This is the example from another species - feathers with high reflectance in UV, also emit blue fluorescence (under UV).

 

post-29-0-67659700-1498063616.jpg

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Andy Perrin
Alex, in visible light, for hummingbirds, the colors are certainly due to iridescence. For example, see the video by biologist Sean Graesser, showing the strong directionality of the reflection from hummingbird feathers. Whether that is true of all species and how that affects the UV reflectance is up for debate, however.
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Alex, in visible light, for hummingbirds, the colors are certainly due to iridescence.

 

We are talking about parrots here.

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Andy Perrin
It doesn't seem like a huge stretch to guess that parrot colors may also involve iridescence. I just don't have a nice video of it. But to each their own.
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Guessing and having a proof are two different things. Are you sure that there is no chemical color involved? How do you explain fluorescence if the color is determined only by iridescence?
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Andy Perrin
Oh, no, I'm not at all sure that there is no chemical color involved, in fact I suspect it affects the results also. Iridescence and absorption coloring aren't mutually exclusive. (See the Baader itself, for example, which uses absorption in the glass part, but interference in the dichroic coating.) The way to really demonstrate what is going on is to microscopically examine the feathers at the range of wavelengths in question, and also try to chemically check for the possible pigments. Without knowing the structure and chemistry, it's all speculation.
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Alex always asks us "teaching" questions! B) I am supposed to be packing camera gear for our travels, but I had to take a moment to read a bit about Structural Color on WickedPete.

 

The UV light reflected off the different level micro surfaces in the parrot's feather can either add or subtract. So is it possible that the Visible light we capture is partly iridescence and partly fluorescence? How does one tell the difference? You would need to use raking UV light shined from different directions and capture photos of each. If the color changes between photos, then structural colour or iridescence. If the color is stable, then fluorescence?

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Aha! All is revealed in the following

 

Parrots: The Animal Answer Guide by Matt Cameron

JHU Press, 2012

 

Page 32: Blue in parrot feathers is a structural color.

 

Page 34: What are the benefits of UV vision?

Sexual signaling and protection from predator raptors who can't see UV as well as parrots.

Experiments showed that female parrots prefer males with some UV-reflectivity.

 

Page 35: Do glowing parrots really exist?

Co-location of UV reflective and fluorescent plumage is widespread among Australian parrots. [Rosella parrots are Australian.] Some experiments showed that the fluorescence functions as a sexual signal. Others showed the opposite. Methodology differences may explain the conflicting results.

 

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It is a l w a y s about mating. :D :rolleyes:

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