Figure 2.

Raman spectra from feather pigments and an unpigmented feather. Five chemical classes have previously been recognized as feather pigments: porphyrins (Livingstone's turaco), tetraterpenoids (carotenoid, bokmakierie), linear polyenals (psittacofulvin, rose-ringed parakeet), metal oxides (iron oxide, sandhill crane) and indole polymers (eumelanin, lilac-breasted roller; phaeomelanin, American robin). Spectra from known pigments and unpigmented β-keratin (greater black-backed gull) differ from the spectrum recovered from yellow penguin feathers (‘spheniscin’), which represents a sixth class of feather pigment. Images of a Knysna turaco and kelp gull are shown; other bird images match the respective feathers. The porphyrin spectrum is from extracted pigment; all other analyses were in situ. Spheniscin, porphyrin, carotenoid, psittacofulvin and β-keratin spectra were measured at 780 nm; melanin-containing spectra were measured at 1064 nm. ‘Spheniscin’, carotenoid and β-keratin spectra have been baseline corrected. Unmanipulated spectra are available in the electronic supplementary material. King penguin photo by Liam Quinn and sandhill crane photo by Tom Friedel. Other photos by D.B.T. (Online version in colour.)