What Causes the Angle-Insensitive Colors in Bird Feathers and Butterfly Wings?

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Discussion Overview

The discussion centers on the mechanisms behind the colors observed in bird feathers and butterfly wings, particularly focusing on why these colors appear angle-insensitive despite being attributed to interference phenomena rather than pigments. The inquiry explores theoretical and experimental aspects of color generation in these biological structures.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants suggest that the colors in bird feathers and butterfly wings are primarily due to interference in microscopic structures, questioning the typical angle sensitivity associated with such colors.
  • Others argue that the presence of both pigments and iridescence in feathers, as seen in chickens and ducks, indicates a more complex interaction rather than a simple dichotomy.
  • A participant highlights the need for clarification on the nature of the angle insensitivity of these colors, indicating it as a core aspect of the inquiry.
  • Different mechanisms for generating interference are mentioned, with diffraction gratings being angle-sensitive and thin films being less so, suggesting variability in how colors might be produced.
  • Concerns are raised about the accuracy of literature attributing these colors to interference, with some participants questioning if the existing understanding is flawed.
  • It is noted that colors produced through interference do not necessarily have to be angle-insensitive, referencing earlier posts to support this point.

Areas of Agreement / Disagreement

Participants express differing views on the mechanisms behind the colors, with some supporting the interference theory while others highlight the role of pigments. The discussion remains unresolved, with multiple competing perspectives present.

Contextual Notes

There are limitations in the discussion regarding the definitions of interference mechanisms and the assumptions underlying the angle sensitivity of colors. The complexity of color generation in biological structures is acknowledged but not fully explored.

Alfred Cann
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I have long been puzzled by the colors of bird feathers and butterflies. They are mostly attributed to interference in microscopic structures, not dyes, yet do not display the typical change of color with viewing angle of interference colors. Why? There are a few exceptions; some butterfly spots and humming birds are iridescent; I am not concerned about those.
 
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Alfred Cann said:
Summary:: Colors of bird feathers and butterfly wings

They are mostly attributed to interference in microscopic structures, not dyes, yet do not display the typical change of color with viewing angle of interference colors. Why?
I think this is far too simplistic. Chickens and ducks have both pigments and iridescence in their feathers. It isn’t an either-or phenomenon; both are present in the same animal and even on the same feather.
 
Alfred Cann said:
[The colours] do not display the typical change of color with viewing angle of interference colors. Why?
This appears to be the core of the question.
Can you expound on what you're asking here?
 
There are different ways of generating interference. Diffraction gratings are quite angle sensitive, thin films (fabry-perot) less so.
 
Alfred Cann said:
yet do not display the typical change of color with viewing angle of interference colors. Why?

See this video at 4:39:

 
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1. Most bird and butterfly colors appear quite angle-insensitive, not even Fabry-Perot. Is the literature wrong that I have read, that attributes these colors to interference?
 
Alfred Cann said:
1. Most bird and butterfly colors appear quite angle-insensitive, not even Fabry-Perot. Is the literature wrong that I have read, that attributes these colors to interference?
Colors through interference don't have to be angle-insensitive. See post #5.
 
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