Birds that appear purple certainly exist, but the color is rarely a simple chemical dye deposited in the feather. The visual effect of purple plumage is often a trick of the light, relying on intricate biological architecture within the feathers themselves. The coloration is highly variable, shifting from deep violet to a bluish-black depending on the angle of the sun and the observer’s position.
Identifying Birds That Appear Purple
Many birds carry the color purple or violet in their common names. The male Violet-backed Starling is a prime example, displaying brilliant, iridescent violet feathers on its head, back, and wings that contrast sharply with its pure white underparts. This bird, found in sub-Saharan Africa, often looks like a jewel when light catches its surface.
The Purple Martin, North America’s largest swallow, is named for this color, although its plumage is technically an iridescent, glossy blue-black. In certain light conditions, the male’s feathers diffract light to create a rich, deep purple sheen. The Purple Gallinule, a marsh bird, has deep violet-blue feathers covering its head and neck. This intense coloration causes the plumage to shimmer, sometimes shining green and turquoise in bright sunlight. The Violet Sabrewing, a large hummingbird, also exhibits rich shades of purple and green on its throat and crown, which are used in courtship displays.
Pigments Versus Light The Science of Avian Color
Avian colors are created through two distinct mechanisms: pigmentary colors and structural colors. Pigmentary colors are produced by chemical compounds deposited within the feather cells, such as melanins for blacks and browns, or carotenoids for reds, yellows, and oranges. These colors are chemically stable and do not change regardless of the viewing angle.
Structural colors are not made by chemical dyes but by the physical arrangement of microscopic structures within the feather. Blue, violet, and iridescent colors are almost exclusively structural, created when light waves scatter as they hit nanostructures of keratin and melanin granules inside the feather barbules. The feather acts like a prism, selectively reflecting the shortest wavelengths of light (blue and violet) while absorbing the others.
The purple hue is typically achieved through a combination of both mechanisms. A feather’s structural components scatter blue light, and this nanostructure is layered over an underlying pigmentary layer, often a red or magenta carotenoid. When the structural blue light mixes with the underlying red pigment, the human eye perceives the combination as purple or violet.
Why True Purple is Exceptionally Rare
The rarity of purple is rooted in the chemical pathways available to birds for synthesizing color. Unlike plants, which use anthocyanin pigments to create true purple, birds lack the necessary metabolic machinery to synthesize a stable purple pigment. If a bird were to rely solely on a pigment, it could not be purple.
The majority of purple coloration in birds must rely on the combination of structural blue and red pigment. This reliance on exact physical and chemical layering makes the color inherently less common than colors produced by a single pigment. A notable exception is a group of South American birds called Cotingas. They modify a dietary yellow carotenoid into a unique purple carotenoid, allowing them to display a deep, solid purple or magenta. This is one of the few instances of a truly pigmentary purple in the avian world.