Iridescence in bird feathers occurs due to a phenomenon called structural coloration. The feathers contain microscopic layers of keratin and air pockets that create something called a photonic crystal structure. This structure:
- Breaks up light into different wavelengths
- Reflects specific colors at different angles
- Creates shifting color effects as the viewing angle changes
Famous examples include hummingbirds’ gorgets (throat patches), peacock feathers, and the neck feathers of pigeons and doves. The exact colors produced depend on the precise spacing and arrangement of these microscopic structures. This is why the same feather can appear different colors as the bird moves or as your viewing angle changes.