Feather Function: What do feathers do?
Each feather on a bird’s body is a finely tuned structure that serves an important role in the bird’s activities. Feathers allow birds to fly, but they also help them show off, blend in, stay warm, and keep dry. Some feathers evolved as specialized airfoilairfoilwinglike structure that produces lift and drag as it moves through the air for efficient flight. Others have been shaped into extreme ornamental forms that create impressive displays but may even hinder mobility. Often we can readily tell how a feather functions, but sometimes the role of a feather is mysterious and we need a scientific study to fill in the picture.
photo: Roseate Spoonbill by Don Bindler
The primary and secondary wing feathers, or remigesremigesREM-i-jeezthe flight feathers on the wing that are attached to bone rather than only to skin, permit birds to take to the skies. Unlike other feathers, remiges are anchored to bone with strong ligamentsligamentband of tissue that connects a bone to another bone, piece of cartilage, or feather so they can withstand the demands of flight and be precisely positioned. The primariesprimaryone of the feathers occupying the outer half of the wing that can be controlled to generate forward thrust during flight are longest of the flight feathers. They occupy the outer half of the wing, can be controlled and rotated like rigid fingers, and provide most of the bird’s forward thrust. While secondariessecondaryone of the feathers occupying the inner half of the wing that overlap with other secondaries to form an airfoil that provides lift during flight cannot be controlled as extensively, they provide most of the lift by overlapping to form an efficient airfoilairfoilwinglike structure that produces lift and drag as it moves through the air. Tail feathers, or rectricesrectricesRECT-ri-seestail feathers, are also classified as flight feathers. They are essential for steering, but only the two most central feathers attach to bone.
Of course not all birds fly; the wing feathers of flightless birds like the Common Ostrich (Struthio camelus) have evolved to be fluffy and ornate rather than tightly interlocking to support flight.
photo: Common Ostrich by Nick Dean1
from left: Wood Duck by Melissa Groo, King Bird-of-Paradise by Tim Laman
Some feathers are so highly modified for display that they almost don’t look like feathers at all. For example, the iridescent spiral from a King Bird-of-Paradise (Cicinnurus regius) tail functions as an ornament in the male’s courtship display. Structurally, the feather is bizarre, with a bare rachisrachisRAY-kissthe stiff central shaft of a feather from which barbs branch that ends in a tight spiral of barbsbarbone of the main branches off the central shaft of a feather and barbulesbarbulebarb-YOOLone of the secondary branches off a feather barb arranged only on one side of the rachis to form an eye-catching brilliant medallion.
Modified contour feathers on the head are also commonly used in courtship displays. For example, the male Wood Duck’s (Aix sponsa) crest forms a colorful fan that completely changes its head shape. During this transformation, the bird elevates thousands of tiny feathers in unison by manipulating muscles just under the skin.
Not all fancy feathers are used to woo a partner; some are used in displays of aggression. For example, Blue Jays (Cyanocitta cristata) keep their crests lowered when they are at rest or with family and flock members, but raise them during aggressive interactions.
photo: Blue Jay by Bill McMullen
photos from left: Eclectus Parrot by cuatrok77, Common Potoo by HarmonyonPlanetEarth
The drab contour feathers covering the body of some birds may seem lackluster, but subtle brown patterns can create an impressive degree of camouflage in forested environments. Famous for hiding in plain sight, the Common Potoo (Nyctibius griseus) is covered with feathers that mimic the colors of the tree branches it perches on. Adding to the disguise, the potoo will adjust its posture and close its eyes into tiny slits, making itself appear to be an extension of the tree.
Not all camouflage has to be drab. For example, the vibrant green contour feathers of male Eclectus Parrots (Eclectus roratus) serve a camouflage function during foraging trips in the rainforest canopy. Back at the nest cavity where the green stands out against the brown tree bark, the male coloration aids in the intense competition with other males to win female mates. Male Eclectus Parrots likely evolved their green coloration as a tradeoff between effective camouflage and display. This is a rare example of feathers that allow birds to both hide and show off.1
photo: Mute Swan chicks by Mike Scott
Have you ever wondered why some birds hatch naked while others are covered in a coat of fuzzy feathers? Many young water birds must be able to swim and forage alongside their parents almost immediately after hatching. These precocialprecocialpree-KO-shuldescribing a chick that is mobile quickly after hatching and requires little parental care chicks hatch with a full coat of natal down to keep them warm in cold water. Young Mute Swans (Cygnus olor) for example, hatch with a fuzzy coat of natal down and after a few weeks, replace the natal down with an inner layer of adult down and an outer coat of contour feathers. In contrast, the young of many songbirds are born completely naked.
These altricialaltricialAl-TRISH-uldescribing a chick that is unable to walk, fly, or swim soon after hatching and requires parental care for an extended period species stay warm by absorbing heat from attending parents and huddling together in an insulated nest. Utterly dependent at hatch, altricial species, like Purple Martins (Progne subis), require lots of parental care.
photo: Purple Martins by OakleyOriginals
Photo: Common Loon by U.S. Fish and Wildlife Service – Midwest Region
Arranged in an overlapping pattern on a bird’s body to expose the waterproof tips, contour feathers allow water to roll right off a bird’s back. Birds constantly maintain their waterproof coat through extensive grooming, or preeningpreenusing the beak to maintain the health and structure of feathers to ensure that every feather is in good shape. The interlocking structure is so important that any disruption to it—such as if spilled oil coats the feathers—leaves the bird waterlogged and helpless. For ducks and birds like the Common Loon (Gavia immer) that spend most of their time in the water, maintaining a waterproof coat is critical for survival.
Photo: Great Horned Owl by Jen St. Louis
Still a mystery
Some feather functions remain a mystery. The feather tufts on the heads of Great Horned Owls (Bubo virginianus) are often mistaken for ears. These modified contour feathers are completely separate from the ear and do not help owls hear, yet there is no scientific consensus on the function of these tufts. Some have proposed that the horns are for display. Others have suggested that owls use them for more complete camouflage while roosting in daylight, but other functions are also possible and no one has yet done a detailed study to find out.2