Figure 1.

(a,b) Photographs of and (c) reflectance spectra from Anna's hummingbird (Calypte anna). (a) Anna's hummingbird facing the observer at nearly optimal viewing geometry, showing highly iridescent gorget and crown feathers (photo by Camden Hackworth). (b) The same hummingbird turned away from the observer, with iridescence greatly reduced at this viewing geometry (photo by Camden Hackworth). (c) Spectral reflectance from a single Anna's hummingbird gorget feather measured with fixed probe and light source and the feather rotated for maximum reflectance (red line), and then rotated away by 5° (green line), 10° (violet line), 15° (blue line) and 20° (orange line). The orange line overlaps the x-axis because the feather is nearly perfectly black when rotated away from maximum reflectance by only 20°. Spectral reflectance was calculated relative to an MgO white standard. Note that reflectance values are well over 100% owing to the high reflectivity and specularity of these feathers in comparison with the diffuse white standard.