Dive into the colorful world of the birds–of–paradise. Learn about how color works, and the ways birds–of–paradise exploit the properties of light to develop bright colors on their feathers, skin, and even inside their mouths.
Many bird-of-paradise feathers get their colors from pigments. Almost all yellow, orange, red, brown, and black colors in birds are due to pigments. Pigments are chemicals that interact with light on a molecular level, absorbing white light and emitting only certain wavelengths. We perceive the emitted wavelengths as the color of the feather. While this may sound exotic, it really isn’t. Pigments are everywhere—paints, vegetables, even our own skin. The makeup of the pigment molecules determines the color emitted. Most of the red, orange, and yellow found in birds are due to chemicals called carotenoids. Most browns and blacks come from melanins, which is the same group that colors mammalian skin and hair.
There are no known blue pigments in bird feathers or skin. Blue pigments are rare in nature because they require metals that are hard to access and can be toxic; but that hasn’t stopped birds-of-paradise from creating stunning blue ornaments. These blues are called structural colors because they are created by the way light interacts with surfaces and spaces on a microscopic scale.
Note: One of the rare examples of a natural blue pigment is the blue in the shells of some bird eggs. This pigment has never been found in skin or feathers.
Sometimes the color in feathers has a now-you-see-it, now-you-don’t quality called iridescence. Displays that use iridescent colors are directional; they only look right from specific angles. When the feather turns a small amount, the color changes hue. When the feather turns a little more the bright color can completely disappear, revealing black or brown pigments within the light-bending layers. Most of the green, blue, and violet feathers in the birds-of-paradise are iridescent.
Some of the colors in birds-of-paradise defy easy categorization. Here are a few examples:
Some birds-of-paradise have a colorful ornament they display only when they open their mouths wide, which they do when calling. The bright colors hidden inside are various shades of yellow and green. We don’t yet know how they make these colors. The yellow could be a pigment, but that’s very unlikely for the greens. It is possible that all mouth colors are variations on the same collagen-rod based structural mechanism that likely creates blue skin. Click through the gallery on the right to see inside seven of the most interesting mouths from across the family tree.
Most female birds-of-paradise have camouflaged plumage. Camouflage is not a default coloration, it is an adaptation. While few predators go after adult birds-of-paradise, plenty of nest predators like snakes and small mammals hunt their eggs and nestlings. Since, in most species, females are the only parents providing care, natural selection favors camouflage for females but not for males. Male plumage is free to respond to sexual selection by becoming showy. The result are male and female plumages that can look like completely different species. Click through this gallery to see some of the inconspicuous female plumages.
Note: It is usually impossible to tell young males from females just by looking at them. It can be five years or more before testosterone levels jump and males grow their adult plumage.
All of the really showy birds-of-paradise are males, but in some of those species females reveal hints of that coloration. In monogamous species there is mutual mate choice so females may show colors as a signal to males that they are a good choice. But for most species of birds-of-paradise, males typically mate with any willing female. In this scenario, female colors are unlikely to be a display. They are more likely a result of less selection for camouflage. And in some cases, like in the blue head of the Wilson’s Bird-of-Paradise, it may simply be hard to uncouple the genes for the blue bald head and feet from sex linked expression, whereas plumage seems to be easier to keep separated by gender lines.
We are very familiar with eye color in humans, and certainly it plays a role in human mate choice. In birds-of-paradise, like most bird species, most eyes are black. But some species have stunning eye colors. The mechanism of producing eye color in birds is different than how it is made in feathers or skin, or even how it is produced in humans. Eye color is produced by pigments deposited in lipid droplets. Sometimes the pigment is in crystal form. These pigments are arranged in structural arrays so that the resulting eye color is both pigmented and structural.
Black & White
Black and white are more than just the absence or presence of full-spectrum light. Each is specific, and the two are often paired to dramatic effect. Click through the gallery to see some examples of this paring.
Black is a result of melanin pigment, but some blacks are more pure and flat than others. It is not clear how many variations of black pigment there are in the birds-of-paradise, but the differences in blacks, from dull to deep, are probably determined more by the microscopic anatomy of the feather surface than differences in black pigment. This is analogous to the way normal black fabric and black velvet may use the same dye but to noticeably different effects.
There is no white pigment in birds. Bright white is structural, but in a different way than other colors. The process is called incoherent scattering and it requires randomness in the keratin along with an absence of pigment. In these circumstances all colors of light are scattered equally and the effect is white. But just as with blacks, there are dirty whites and bright whites. The brightness of the white may be due to the complete elimination of all traces of pigment, or it may be due to a more effective scattering array.
Not unlike photo paper or wall paint, feathers come in a range from matte to semi-gloss and glossy. Nowhere is this variation more apparent than in the variety of blacks in the birds-of-paradise. Some blacks, like the Paradise-crow, genuinely are flat and reasonably described as drab. Many of the manucodes have a sheen to them that is iridescent, though not in a coherently directional way. All of these variations are due to small differences in the microscopic structure of the feathers. Not much is known about the specifics of the mechanism of these variations, nor of the adaptive value of glossiness.
The example at right shows a range of blacks from glossy to flat. Click through the images to see the blacks from some of the least colorful birds-of-paradise.
After all of this, it is reasonable to ask whether birds see these colors the same way we do. The answer is that they see all we see and more. While no one has specifically examined the vision of a bird-of-paradise, birds have better color vision than people in two ways.
- Most birds have four kinds of color receptors (called cone cells) in their eyes. We have three. The extra kind allows them to see into the ultraviolet spectrum, where they can sense entire visual signals that are imperceptible to humans. It is entirely possible that there are color ornaments that are critical to the birds, but totally invisible to us.
- Birds also can discern smaller differences between colors than people can. That’s because they have oil-droplet filters that sharpen the sensitivity of each kind of cone cell.
So as bright as their world looks to us, it might look even brighter to them!