During the breeding season, only the head of the indigo bunting (Passerina cyanea) is actually indigo. In season, adult males actually have black feathers, but the diffraction of light by the feather structure makes them appear to be a brilliant blue, which is why males can appear many shades from black to blue to turquoise. As is often the case, the female is much duller - just a plain brown. The indigo bunting migrates at night, using the pattern of stars nearest the North Star to guide them.
