Figure 2.

Spectral reflectance curves (±1s.e.) of cresol-treated breast feathers of American Goldfinches (a) against a black background after being chemically de-pigmented (b) against a black background intact, and (c) against a white background intact. Panel A shows that de-pigmented feathers became transparent after cresol treatment, as their reflectance matched that of the black background after being treated with cresol, except for a small increase in overall reflectance. Panel B shows that cresol-treated yellow feathers against a black background are nearly transparent with a faint yellow cast, as indicated by the small increase in brightness from 500 to 700 nm. c shows that cresol-treated yellow feathers against a white background are once again bright yellow, as carotenoids absorb light from the white background. n=5 for all feather reflectance curves. Because all feathers were measured on the same piece of background paper, n=1 for these curves.