This story is brought to you by BirdNote, a show that airs daily on public radio stations nationwide. 3179 When a perched male Ruby-throated Hummingbird raises its head toward the sun at just the right angle, its throat glitters like a crimson spotlight. When it turns its head slightly, the bird’s throat no longer gleams. It appears colorless, dark. A hummingbird’s brilliant throat feathers are called its “gorget” (pronounced gor-jit). The term comes from days of old, when a knight-in-armor wore a metallic collar—or gorget—to protect his throat. The hummingbird’s intense glint is the result of iridescence, rather than colored pigments. The bird’s throat feathers contain minutely thin, film-like layers of “platelets,” set like tiles in a mosaic against a darker background. Light waves reflect and refract off the mosaic, creating color in the manner of sun glinting off oily film on water. "There he goes! Diving in display toward the female. He plunges...