When one is described as having "a feather in one's cap," a commendable and distinctive accomplishment has been earned. The feather, today unique to the animal group, birds, evolved to enable birds to flourish. Therefore, the feather represents a vital structure worthy of awe and praise.
Feathers serve four commonly known functions. Besides providing lift for flight, feathers insulate and waterproof birds to keep them warm and dry. Feather coloration provides camouflage so a bird is concealed while stalking potential prey or hiding from predators. Lastly, feather coloration is critical in sexual selection for mating.
Recently, on a vacation to Jekyll Island, Ga., I was able to observe a male painted bunting, a gaudy, but attractive, sparrow sized seed eating bird described as having a dark blue head, bright red chest, belly and rump, and bright green back. It is beautiful and unforgettable. The female, colored a bright green-yellow was observed at the same time. So how did the painted bunting or any other colorful bird develop multiple colored feathers?
This image shows examples of pigment deposition in natural feathers creating a repeating pattern or barred appearance. The feathers presented left to right are from a mallard duck flank, pheasant tail, peacock, mallard duck wing and neck of my former pet rooster, Ferdinand.
Photo by Robert M. Ungerer
Fossil records reveal small dog-sized dinosaurs with short feathers living 120 million years ago, 60 million years before Tyrannosaurus rex roamed the Earth. The evidence that birds evolved from dinosaurs, a reptile, is quite strong. Feathers, beaks and claws are composed of beta keratin, a protein, which is also present in the claws, scales and shells of current day reptiles.
Feathers develop from tiny follicles in the outer skin similar to hair follicles on human or mammalian skin. The stiff long shaft down the center of a feather is called the rachis to which barbs branch off on each side. Each barb is interlocked to the adjoining barb so the feather has stiffness allowing wing flapping to launch a bird into flight.
My simplified theory regarding evolution of colorful male feathers and drab female coloration starts with a mutation in the male creating a color change, perhaps a brighter shade than usual. Since birds see color, unlike most mammals, females find this male more appealing to mate with instead of the less colorful male. Male offspring of this mating likely inherit the color change which will be appealing to other females prompting a mating and a more widespread production of more colorful males. Over thousands of generations colorful males will be chosen to breed leaving the less colorful males out of breeding altogether, eventually dying out forever.
Natural feather coloring is produced by several processes. Melanins, synthesized from amino acids, produce dull red, gray, black and brown colors pigments. Bright red, orange and yellow colors are produced by ingestion of different plant chemicals called carotenoids just like eating an excessive amount of carrots containing carotenoids turn human skin orange. Bird species are capable of altering ingested carotenoids to produce different shades of color. The colors from melanins and carotenoids are deposited in specific regions of a feather creating a barred pattern seen in pheasant flight and tail feathers. A "National Geographic" article from February 2011 describes this process as "incredible precision of laying down one color on a few barbs while the same barbs receive a different color just a few millimeters away. Can you imagine if one human hair strand could be brown, red and yellow at the same time like a feather?
Besides producing color, melanins provide structural strength to a feather. This is evident in the wing of a seagull; the black tip of a white wing shows less wear than the white portion of the wing. Blue color evident in blue jays and bluebirds is produced by suspended particles in small open spaces in the feather barbs which cause light to be scattered and reflected. Most birds produce green color by blue overlaying yellow carotenoids. Finally, the red throat of the ruby-throated hummingbird, seen locally, is the result of interference and reinforcement of certain light wavelengths striking the throat feathers at an angle, called iridescence.
Since the feather is vital to bird survival, it is a praiseworthy object; therefore a feather in one's cap symbolizes an earned distinction that is not lightweight.