Melanins are found in the skin and feathers of birds as microscopic colored granules. Melanins can produce colors ranging from the darkest black to reddish browns and pale yellows, depending on their concentration and location.
The blue tones found in the feathers of Steller’s Jays, Mountain Bluebirds, and Indigo Buntings are considered structural hues. You can observe how this operates for yourself if you find a Steller’s or Blue Jay feather. When you first look at the feather in normal lighting, the expected blue color will be visible. Next, try back-lighting the feather. Light passing through the feather will cause it to appear brown. Because the light isn’t being reflected back, the blues are gone, and the feathers’ melanin makes the brown appear.
Birds are color-blind, as one might expect from the astounding variety of colors and patterns displayed by the more than 10,000 bird species worldwide. There are two ways that pigments or light refraction brought on by the structure of the feather combine to form the colors in a bird’s feathers. Feather colors can occasionally be the result of a blend of structural and pigment colors. Certain parrots have green coloration due to yellow pigments covering their blue-reflecting feathers.
Animals and plants both contain colored materials called pigments. Pigments produce coloration that is distinct from the feather’s structure. Three distinct groups contribute to pigment coloration in birds: carotenoids, melanins, and porphyrines.
Not all structural colors are iridescent. Small air pockets in feather barbs can scatter light, giving the feathers a distinct, non-iridescent color. This is how feathers almost always get their blue colors. The blue feathers of Steller’s Jays, Blue Jays, Indigo Buntings, and Bluebirds are a few examples.
The role of melanins in creating complex plumage patterns in 9,000 species
Feathers, or plumage, are among the most remarkably diverse features of animals that are visible to the unaided eye in birds. Bird feather patterns are composed of complex arrangements of mottles, scales, bars, and spots. But, how are these colors and patterns made?.
We already know why birds have colored feathers. Many birds’ plumage colors help them blend in with their surroundings, which reduces their visibility to predators, or stand out from their peers, which attracts potential mates. These aspects are well known. How the patterns are made at the cellular level has proven to be a more enigmatic process.
Dr. Ismael Galván and his group of knowledgeable scientists examined plumage coloration to determine what kinds of pigments were used in birds’ intricate feather designs. Melanins, which yield a variety of colors including black, grey, brown, and orange, and carotenoids, which are utilized by specific feather structures to produce brighter color hues, are the two main pigment types responsible for plumage coloration.
Birds cannot produce carotenoids on their own. Birds need to eat foods high in these pigments in order to have colorful feathers. The carotenoids in these foods travel through the bloodstream to the feather follicles. The bodies of birds do not directly control the synthesis or deposit of carotenoids, nor do they control the specialized feather structures that respond to the carotenoids they consume in a way that is not controlled by specialized cells.
Conversely, melaninsor perhaps better put, “on the other wing”are produced by unique cells in birds’ bodies known as “melanocytes,” which collaborate with feather follicles to produce a precise control over pigmentation. Although studies frequently focus on carotenoids in bird coloration, Dr. Galván and colleagues are the pioneers in examining if melanins are, in fact, the sole pigmentary component that birds’ bodies can directly regulate at the cellular level.
As Galván states, “We studied the appearance of the plumage of all species of extant birds and determined if the color patches that they contain are produced by melanins or by other pigmentary elements, knowing beforehand that different pigments and structures produce different types of colors in feathers.” We also determined which plumage patterns are complex, which we define as those that are made up of two or more distinguishable color combinations that appear in the plumage more than twice in a row. “The aim of this extensive study, which looked at nearly 9,000 bird species, was to provide evidence in favor of a universal conclusion that would address the question of how birds create intricate and colorful patterns.
The team discovered that approximately 92 percent of the investigated species possessed complex plumage patterns, with the majority of these patterns being primarily produced by melanins rather than by carotenoids. In a metaphorical sense, if the birds were artists, they would utilize melanin as a detail paintbrush and carotenoids as a broad brush to create more elaborate designs.
There are a few exceptions to this rule: complex plumage patterns devoid of melanins are present in three bird families. Fruit doves, cotingas, and one species of stork are known for their unusual colors, which are thought to be caused by metabolic changes made to the carotenoid pigments they eat.
To learn more about this research, see Ismael Galván, Jorge García-Campa, and Juan José Negro’s paper “Complex plumage patterns can be produced only with the contribution of melanins,” which was published in Physiological and Biochemical Zoology in September/October 2017.
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Materials provided by University of Chicago Press Journals. Note: Content may be edited for style and length.
Journal Reference:
- Ismael Galván, Jorge García-Campa, Juan J. Negro. Only Melanin Contribution Is Required to Produce Complex Plumage Patterns Physiological and Biochemical Zoology, 2017; 90 (5): 600 DOI: 10. 1086/693962 .
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