Figure 4: Sulfur oxidation state SRS-XRF mapping of kestrel feather.

(a) Optical, (b) total sulfur (3150 eV), (c) 2476 eV, (d) 2473.5 eV, (e) 2472.3 eV. The total sulfur image shows that sulfur is elevated within and appears to correlate with red pigment compared to the dark stripes. Additionally, the distribution of specific oxidation states are not directly correlated. In particular, the striped pattern is more distinct in c and d compared to e. Pixel size = 50 microns. Map acquisition time = ~20 mins. Scale bar = 1 cm.