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High refractive index of melanin in shiny occipital feathers of a bird of paradise
journal contribution
posted on 2023-06-08, 21:20 authored by Doekele G Stavenga, Hein L Leertouwer, Daniel Colaco OsorioDaniel Colaco Osorio, Bodo D WiltsMale Lawes's Parotia, a bird of paradise, use the highly directional reflection of the structurally colored, brilliant-silvery occipital feathers in their courtship display. As in other birds, the structural coloration is produced by ordered melanin pigmentation. The barbules of the Parotia's occipital feathers, with thickness ~3 µm, contain 6–7 layers of densely packed melanin rodlets (diameter ~0.25 µm, length ~2 µm). The effectively ~0.2 µm thick melanin layers separated by ~0.2 µm thick keratin layers create a multilayer interference reflector. Reflectance measurements yielded peak wavelengths in the near-infrared at ~1.3 µm, i.e., far outside the visible wavelength range. With the Jamin-Lebedeff interference microscopy method recently developed for pigmented media, we here determined the refractive index of the intact barbules. We thus derived the wavelength dependence of the refractive index of the barbules' melanin to be 1.7–1.8 in the visible wavelength range. Implementing the anatomical and refractive index data in an optical multilayer model, we calculated the barbules' reflectance, transmittance and absorptance spectra, thereby confirming measured spectra.
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Publication status
- Published
File Version
- Published version
Journal
Light: Science and ApplicationsISSN
2047-7538Publisher
NatureExternal DOI
Issue
1Volume
4Article number
e243Department affiliated with
- Evolution, Behaviour and Environment Publications
Full text available
- Yes
Peer reviewed?
- Yes
Legacy Posted Date
2015-06-30First Open Access (FOA) Date
2015-06-30First Compliant Deposit (FCD) Date
2015-06-30Usage metrics
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