Bird plumage color basics

Introduction

Plumage, the name for all of a bird's feathers, is often the most striking feature about a bird. Bird plumage colors range from browns, tans, grays, and whites to bright reds, greens, pinks, and blues. The colors, patterns, and shapes of a bird's plumage may have a variety of functions, such as providing camouflage or signaling to a mate. Plumage may also contain features that are outside of the visible spectrum, or the spectrum of colors that humans can see, because most birds can see a wider variety of colors than people can. On this page, we will explore the bird color vision and how bird feathers get their colors.

What colors can birds see?

Most birds see a greater range of colors than humans. Humans have three types of color-detecting structures called cones in their eyes. These cones can detect three colors: red, blue, and green. This is known as trichromatic vision. The spectrum of colors that humans can see can ranges from violet to red, a spectrum of light known as the "visible spectrum." When expressed in wavelengths of light, humans can see light at wavelengths from about 400 to 700 nanometers.

Birds that are active during the day, however, often have tetrachromatic vision, meaning that they have four types of cones in their eyes that detect color. These cones detect red, blue, green, and UV light. Therefore, birds can see the colors humans can see. They can also see some light in the ultraviolet (UV) part of the spectrum, which humans cannot see. The UV light that birds can seen ranges from wavelengths of about 300 to 400 nanometers. Light in this range is mostly classified as UV-A (long-wave ultraviolet light). To add to their tetrachromatic vision, the cones in bird's eyes also have special oil droplets that enhance their ability to see different colors.

What good is seeing ultraviolet light?

Seeing the UV part of the light spectrum allows birds to see many things that humans cannot see. Some birds have plumage that interacts with UV light. Their feathers may reflect UV light or fluoresce under UV light. When objects fluoresce, they appear to glow under UV, sometimes with bright colors like green or red. UV reflectance and fluorescence can be detected using a blacklight or a special UV filter on a camera. Other markings, such as those on a puffin's beak, may also interact with UV.

Researchers believe that the addition of UV colors may make bird plumage look more vivid to other birds. Sometimes birds have UV patterns that are not visible to the human eye. While we cannot see exactly what birds see, special lighting techniques or images with modified colors can give us an idea of how plumage that reflects or glows under UV light might look to a bird.

The ability to see UV light also helps some birds of prey to hunt. For example, the urine of a type of rodent known as a vole reflects UV light. Eurasian kestrels, a type of raptor, can look for the urine trails of voles to determine if a particular area is a good hunting ground.

UV colors show up elsewhere in the natural world. For example, some flowers have ultraviolet patterns that are thought to signal to bees, which can see UV light, where they can find nectar. Some mammals are known to have fur that glows under UV light. Although some mammals can see UV light, the function of fluorescent fur in mammals is not entirely clear. In fact, the glowing fur of these animals may not have a purpose, but may simply be a byproduct of their fur structure and color. Some reptiles and invertebrates—most famously, scorpions—also fluoresce (glow) under UV light.

How do bird feathers get their colors?

Pigments

Some feather colors are produced by pigments, compounds deposited in a feather that reflect certain wavelengths of light. Colors like yellows, oranges, reds, browns, blacks, and some greens are created by pigments.

Some of these pigments, like black, brown, yellow, gray, and reddish melanins, are produced by the birds themselves. Eumelanin makes darker colors, like dark brown and black. Pheomelanin makes lighter colors that are reddish or yellowish. These pigments are also found in other types of animals, including humans, where they occur in skin, hair, and eyes. In birds, melanin also strengthens feathers.

Birds feathers get some colors, namely yellow, orange, red, and purple, from carotenoid pigments that come from their diets. A good example is the flamingo, which gets its pink color from eating certain types of algae or shrimp. A few other types of pigments can give feathers red, yellow, or occasionally green colors. The turacos, an unusual group of African birds, have copper-containing green and red porphyrin-based pigments.

Structural colors

Structural colors are not produced by pigments. Instead, they are produced by the structural characteristics of a feather, which reflect certain wavelengths of light. Ultraviolet, white, blue, purple, iridescent, and most green colors in birds are structural.

Feathers with structural colors often also contain pigments, like black or gray melanins. These pigments absorb the colors that are not reflected by the feather structures. Pigments can also combine with structural colors to produce a third color. For example, a feather with yellow pigment and blue structural color will appear green.