As humans, feathers have captured our imagination. As Emily Dickinson wrote, “‘Hope’ is the thing with feathers -/That perches in the soul.”
Humans use feathers for decor, warmth, weapons, religious ceremonies, symbolism, and cultural traditions.
A single feather might have more color than most paintings, more engineering finesse than many human inventions, and are just made of the same stuff as fingernails.
Silly Question: What’s a Feather?
Feathers are the most complex skin structure in any vertebrae. They are extensions of keratin growing on the epidermis to create a huge variety of structures. Part of what sets feathers apart from, say, quills on a porcupine, are the potential that feathers have. They have the potential to become their classic structure, which would be made of many mechanisms, structures, and parts. The classic feather, also known as a wing feather or a flight feather, has the classic distribution of barbs to make up the vane.
At the base, the barbs may soften and disperse to become downy. However, feathers don’t have to look like this. Since their origin, they have looked complex or simple. To learn more about the feather, we must think about a time before birds, before feathers ever reached the skies.
The Dinosaur Protofeather
When artist Yusuke Murata (better known as an the illustrator of the manga One-Punch Man) depicted feathered dinosaurs, he pulled no punches.
Unfortunately for our vast imaginations, there’s no real evidence that the T-Rex had full body feathers. In fact, preserved skin distinctly show rough scaly skin, similar to how we often imagine them. If it had feathers anywhere, it’d be on its back and spine, where they don’t have skin impressions. However, Murata’s imagination wasn’t too far-fetched. Close ancestors and cousins of the T-Rex were feathered.
In fact, feathers are almost intrinsic to the evolution of all dinosaurs. The very ancient common ancestor grouping, Dinosauria, is found to universally have the ability to grow feathers. This was the most ancient predecessor to the T-rex, sauropods, triceratops, and pretty much every dinosaur we can think of. Now, this doesn’t mean all dinosaurs have feathers. For example, Dinosauria is also the ancient ancestor to crocodiles, who do not have feathers. But it points to the possibility that there are more feathered dinosaurs than we previously thought.
It only took this long to realize because feathers are so difficult to fossilize. In fact, this was only originally known because feather quill knobs were found in some dinosaur bones. This later led to the realization that all velociraptors are covered with vaned, colorful feathers. As said in National Geographic: “A velociraptor without feathers is not a velociraptor.”
However, our idea of a feather is pushed to some limits with its earliest forms. Many protofeathers are more likely to resemble quills than our modern perception of a typical feather. (However, the porcupine quill of course evolved separately in the mammalian rodent lineage)
These protofeathers might be compared to newly grown feathers after a molt. These pin feathers are often colorful, thick, spiny, and without vane filament. They can be long or short. However, they are also irrevocably still feathers. In part, because their evolution implies an inseparable connection to the developed, recognizable modern feather. They the same evolution, development, and basic make up.
The issue is, the rachis is much more likely to last than any vane or plume attached to it. If you press a delicate feather into some mud and left it there for a million years, most likely just the rachis will leave a fossilized impression. So the pin-like protofeather may not have been as common as we currently think. It’s difficult to say for certain what many dinosaur feathers looked like — in color, size, and function. Only more discovery and a little luck will tell us.
Flight Feathers
A statement everyone can agree with: Even if the T-rex was covered in feathers, it couldn’t fly. However, feathers are also not required for flight (see: bats and pterosaurs), but they certainly help. Some potentially flying dinosaurs had flight feathers, such as the archaeopteryx.
Considering the huge diversity in types of flight — from powerful force lifting 33 lbs of Andean Condor to the delicate hovering of a .05 oz bee hummingbird — flight feathers are strikingly similar. It’s a one-size-fits-most model, with small variations to accommodate different needs. The rachis acts as a mast holding the sail of the vane fibers. The vane fibers are linked together to create that continuous sail texture, with tight barbs holding each other like velcro. In fact, when forcibly separated, it even makes a velcro-like sound.
This extraordinarily small, tight sail-like status of the feather vane make it the perfect tool for flight. Flexible yet stable, generating thrust in flap or streamline in glide positions. One can imagine that the archaeopteryx lineage refined these techniques and micro-level details to produce the wide-range of types of flight birds exhibit today.
Not only is the feather important to flight, but also the way the body controls the feathers. The basic engineering and shape of the feather allows for flapping for thrust, or angled streamlining for gliding and steering. Even humans can’t tap into it, with flap-based flight being something we cannot meaningfully reproduce for commercial flight. Instead, we rely on immense raw engine thrust and gliding.
Other Functioning Feathers
There’s a high variety of function for feathers too. Look at a penguin, and clearly, feathers aren’t exclusively for flight. Temperature regulation, waterproofing, anti-parasitics, identification, swimming streamlining, flight, camouflage, and UV light protection are just to name a few.
Temperature control keeps birds cool enough and warm enough. Their wings can be used to beat the air and cool the space around them. Their feathers block the sun’s harmful rays. However, feathers also keep birds warm. Emperor Penguins, with their thick layer of down, can thrive in “temperatures as low as -60°C (-76°F) and blizzards of 200 km/h (124 mph).”
Down feathers are a well-known heat insulator in birds, often found all over many baby birds, or as a bottom layer beneath other feathers in adult birds. However, down is not just for warmth. A few types of birds have a specialized type of feather, called “powder down,” which purposefully disintegrates on the bird. The powder coats the other feathers, producing both a waterproofing and also an anti-parasitic effect. If you know anyone with a pet parrot, they’re one of the only birds who have powder down!
Powder down isn’t the only antiparasitic function of feathers. The nature of feathers themselves initiate preening. Birds purposefully “unzip” feathers, or disconnect the “velcro” of the barbs. When they preen, they zip the barbs back together, and coat their feathers with oil from their preen oil gland, at the base of their tail. The preen oil not only hydrates, but waterproofs the feather. Furthermore, the inherent shape of the barbs mean that when they are reconnected, the feathers themselves push off parasites or infiltrates. The preening instinct is strong, with social, breeding, and flight-maintenance functions as well.
Finally, bristle feathers create a frame around the mouths and eyes of birds. These highly irritable whiskers keep dust and wind out of the eyes and nostrils, but also keeps bugs and parasites away.
The colors of a bird’s feathers can have a variety of functions. It’s a balance of: be noticed, or be hidden, or both. Coloration selection tends towards hiding, with a majority of birds prioritizing camouflage.
The aesthetic feather function isn’t appreciated by everyone. “The sight of a feather in a peacock’s tail,” Charles Darwin wrote in 1860, “makes me sick.”
However, a flourishing bird environment, such as the tropics (where peafowl-like drama often occurs) creates a multitude of colors, plumage, and long decorative feathers. This almost seems contrary to Darwinian evolution, which might consider prioritizing camouflage. One thing Darwin didn’t know was that many animals, birds included, can see into the UV spectrum. The colors we see aren’t always the colors predators or peers see.
Furthermore, birds that can afford to have ridiculously decorated additions are often flourishing within tight niches in abundant tropics. They may have had extended time of peace. A bird with superfluous appendages tells its mates it can afford to be superfluous, and as a result survives well. In a way, it’s bragging in the natural world. Whether via refraction, reflection, or pigmentation, feathers are the perfect experiment in vivid colors, because their structure allows for a huge variety of colors and patterns.
Colorful or camouflaged. Fancy or functional. Flying or flightless. Ancient or in our backyard. Feathers’ huge variety developed through millions of years of evolution. With the pressure of cities, suburbs, and industry pressuring birds to adapt even further, their feathers keep them as a dominant, persistent creature on all continents.
