On this episode of Wildlife Weekly, Jackie Sandberg explains the structure and colors of bird feathers. The colors of a bird’s feathers can be changed by its diet. For example, the type of berries cardinals eat will change the hue of their red feathers.

The exception is blue feathers, which are not affected by diet. Blue is a color of bird feather that is determined by cellular structure that influences the visibility of light. The keratin that makes up the feathers grows in a structure that cancels out red and yellow wavelengths, creating a blue tone. The bright coloring in many male birds, such as peacocks, is functional, and is believed to be used to attract females.  Iridescence is caused by prism-like structures in the feather, refracting light in a way that causes different shades depending on the viewing angle.