Feathers- Part One
By Jon Friedman
Of all living organisms on the planet, only birds have feathers. This is an interesting and amazing fact. Feathers have many uses and perform various functions, come in many forms and colors, and are absolutely necessary in order for birds to not only survive, but thrive! Feathers are essential for almost all aspects of bird life. From birth to death, feathers define the bird and allows for a successful life. Feathers are so important in bird life that nearly all species spend a major portion of their daily waking hours engaged in cleaning and preening their feathers. Their success in leading long and productive lives depends upon their feathers.
Even without any specialized knowledge, nearly everyone can appreciate the beautiful shapes and colors of feathers that help define all birds. And, while much of a bird’s beauty can be attributed to its plumage, feathers perform many other functions at the same time. Plumage is primarily responsible for mating displays, camouflage and concealment, waterproofing and buoyancy, aerodynamic shaping of the body for flight, thermoregulation for both heat and cold, protecting skin from injuries, and protection from the sun’s harmful UV rays of light.
The Origins of Feathers
Birds may not be the only animals that have developed the ability to fly, but they are the only animals to have feathers. There is still debate in scientific circles as to the exact circumstances that led some dinosaurs to evolve into feathered creatures and ultimately shed the last remaining reptilian characteristics and become birds as we know them today. There is, more or less, general agreement that scales eventually became feathers and some cold-blooded reptilian dinosaurs ultimately became warm-blooded birds. Two major theories of bird evolution have dominated scientific thought until recent years.
The “Trees-down” theory, in very simple terms, believes that birds originated as tree-dwelling dinosaurs, developing talons that could grip branches and thus enable them to live high in tree canopies and thereby avoid contact with deadly ground predators. Feathers developed from their reptilian scales, allowing them to glide from tree to tree without having to travel on the ground, much like flying squirrels. Staying higher up in the trees also enabled early birds to avoid predators that were limited to the ground. True flying developed later, after they discovered/learned that flapping would keep them airborne longer and enable them to travel greater distances.
The “Ground-up” theory presents early birds as strictly ground-dwelling, bipedal predators that chased down their prey on foot. Feathers, under this theory, developed primarily and at first as insulation to retain body heat. This theory also states that feathers played a part in helping these birds both maintain balance while running by increasing the surface area of their extended forelimbs and their ability to more effectively pursue prey. As feathers grew enlarged over time, they developed into airfoils that enabled early flight.
Fossil discoveries of prehistoric specimens such as Archaeopteryx support the first theory and fossils of theropod dinosaurs support the second theory. In very recent years, many scientists are realizing that both theories hold promise and the facts may reveal that some combination of the two may be the correct theory. Very recent fossil discoveries from China support this latest theory.
Number of Feathers
Birds are defined by their feathers – no bird lacks them and no other animal possesses them. Flight requires lightness. Feathers have hollow quills and contribute only about 6 to 9 per cent of a bird’s total weight. By contrast, their lightweight and hollow bony skeletal materials weigh more than twice as much as their feathers. Birds produce feathers in very large numbers. Typically, the larger the bird the more feathers it possesses (not counting the multitude of down feathers). Hummingbirds have about 1000 feathers on average. Swans are known to have over 25,000 much larger feathers.
Several naturalists have made painstaking individual counts of each and every contour feather on a number of species over the past century or so. The actual count of the least amount of contour feathers was from a Ruby-throated Hummingbird captured in Washington, D.C. in 1949. It had exactly 940 feathers. The most amount on a bird, 25,216 feathers, were counted from a Whistling Swan, in Michigan in 1937.
Other examples from the historical record include, but are not limited to: 1,119 feathers on a Ruby-crowned Kinglet; 4,607 feathers on an Eastern Meadowlark; 4,915 feathers on a Brewer’s Blackbird; 3,235 feathers on a Bobolink; and 3,557 feathers on a House Sparrow. The researchers who actually did the counts noticed that the same species of birds averaged slightly more feathers in winter and slightly less in summer.
While it is generally true that smaller birds have fewer feathers than larger birds, smaller birds generally have more feathers per unit of body weight than larger birds. This is correlated with the heat-retention needs of smaller birds, which in general have a higher rate of metabolism, as is the case with hummingbirds and chickadees.
Types of Feathers
Contour Feathers are the first feathers we notice as they are the most visible of the six types of feathers birds possess and they are the feathers that give birds their unique characteristic shapes and colors. Contour feathers, much like roof shingles, are arranged in overlapping rows and form a protective outer layer of feathers, shielding their skin and underlying feathers from harm and providing an extremely tight exterior coating that water doesn’t penetrate. Feathers waterproof birds.
Contour feathers are usually the type of feather you may find on the ground, pick up, twirl in your fingers to see both sides of it, and marvel at its intricate construction, unique shape, and colorful and/or distinct markings. These feathers are the ones that enable us to correctly identify the species that feather belongs to. These feathers penetrate the skin, are attached to muscle, and allows birds to hold them tightly against their bodies in warmer weather or fluff them up (trapping a layer of air) to keep them warm in cold weather. Contour feathers are usually quite stiff and symmetrical on both sides – making identification easier. All species have contour feathers. Birds can, due to these feathers being attached to muscle, move these feathers in any number of positions from left to right or up and down.
Down Feathers cover a bird’s body and are usually unseen underneath the exterior covering of contour feathers. Down feathers are distinctive in shape, usually pure white in color, and are responsible for providing insulating value. There are various types and shapes of down feathers, depending upon the bird species but they are generally soft and fluffy, lacking a stiff central shaft. Most of us are familiar with the warmth that down pillows, comforters, and sleeping bags provide which are filled with down feathers. Occasionally, you may find a loose down feather on or near your bed. Similarly, down feathers occasionally escape the bird. It is well known that certain birds also pluck down feathers to line their nests to keep babies warm, especially altricial birds that are born with naked, non-feathered skin. When eggs or babies were left in the nest alone while parents were foraging, they were usually covered in a layer of plucked down to maintain the warm temperature necessary for incubation. Evenly spaced on the body of the bird, down feathers provide excellent insulation by trapping a layer of air between the bird’s body and their exterior contour feathers. Birds whose habitats are found in higher elevations and cold regions depend upon their down feathers to survive cold weather and other similarly harsh conditions.
Down feathers also promote buoyancy for water birds, keeping them warm, dry and afloat. While duck and goose down are commonly used today for feather beds and similar bed gear, it was eider ducks that were historically hunted for their highly-prized down feathers – considered the best insulating of all down feathers.
Natal down covers the entire body of some newly hatched birds, particularly ducks and geese, with a coat of soft yellow down feathers, not white. Shortly after birth, the contour feathers will cover the down. As the bird matures, the natal down will turn from yellow to white.
Powder down is a unique type of feather only found in limited numbers in some species. These feathers are found in clusters among other down feathers, grow continuously, and are not molted. Their tips break down, forming fine, dust-like particles – commonly referred to as feather dust. Pigeons and herons are well known for their powder down. Many parrot species also have powder down. Parrot owners sometimes notice a white dust around their pet’s cages. Some owners develop allergic reactions to this material. It is believed that this powder down helps remove excess oils and debris in feathers, similar to how a dust bath cleanses.
Flight Feathers are sometimes the most obvious of all feathers, especially when observing birds in mid-air. Their primary flight feathers are attached to their wings and resemble long, outstretched “fingers”. Flight feathers are among the least abundant of all the bird’s feathers. Most birds have about 10 primary feathers on each wing.
These feathers have a long, slightly curved shaft and are asymmetrical, with one side wider and one side narrower along the feather’s shaft. The narrower side is the leading or front edge of the feather, which wears more quickly than the back edge. Before the leading edge is completely worn, a molt occurs and the older worn feather is replaced with a new one.
Each wing has a set of secondary flight feathers, as well. These could number as few as six secondaries in hummingbirds and as many as fourteen or more in larger birds – depending upon the bird’s body size and wing length. Secondaries are shorter and less noticeable that primary flight feathers. If primaries can be thought of as “fingers”, then secondaries can be thought of as equivalent to a human forearm. The secondaries are fairly wide. In flight, secondaries may be easily noticeable but while a bird is perched, the primaries usually cover the secondaries.
Covert flight feathers are specialized feathers that cover and protect the base of the wing and tail feathers. They help in shaping the wings and tails and provide warmth. Coverts are much shorter than primaries and secondaries, often blending into these feathers, making them harder to notice as a result.
Semiplume Feathers provide support and filling between the contour and down feathers. They are common in almost all species of birds. They have a strong central shaft, like contour feathers, but they lack the barbules that interlock and connect one feather to another. They are very fluffy feathers that provide excellent insulation. At more than twice the number and size of most regular down feathers, semiplumes typically provide excellent insulation and more actual physical support for the larger contour feathers.
Some species have developed very large and elongated decorative semiplumes. Great Egrets, birds such as the Great Blue Heron, and others have large semiplume feathers. Birds with such large semiplume feathers have historically been hunted almost into extinction for the sake of female fashion. While some military headgear around the world exhibits large semiplume feathers, it was womens hats that dominated the trend in fashionable hats for several decades from the late 19th century into the early 20th century. More about that in part two.
Filoplume Feathers are unlike all other feathers in form and function. They have an elongated shape, from one to several inches long and are generally the simplest of all feathers. They lack the typical barbs of contour feathers, but have a small cluster of barbs at the tip of the feather that is reminiscent of the puff of fur at the tip of a lion’s tail. They are not attached to muscle and can’t be moved independently, like contour feathers. Their long length makes filoplumes extend beyond the contour and flight feathers.
Ornithologists believe that filoplumes sense and transmit information about movement, much as a boat captain can determine wind direction from the sails. They believe that the filoplumes help inform birds about feather position, which helps them make micro adjustments during flight. Some researchers further believe that these feathers also give birds a sense of airspeed.
Further, filoplume feathers are used by some species during the mating season to create more dazzling and elaborate displays. The tufted ends of these feathers stick out above all the other feathers, adding to the impressiveness of the mating display.
Bristle Feathers are exceptional and different from all other feathers in that they serve a completely unique function. They serve a sensory function – much like a cat’s or dog’s whiskers. They are long and stiff with a tapering shaft and more hair-like than feathery. They can be found on different species in different places on birds’ bodies – just about anywhere there is bare naked skin – especially on their heads, necks, and feet.
Bristle feathers are commonly found on flycatchers and other insect-hawking birds as well as nocturnal birds such as owls, nightjars, and nighthawks. These birds have bristle feathers that sandwich their mouths, sensing close-by insects and helping to sweep those insects into their mouths in mid-flight. Most woodpecker species have clusters of densely packed bristle feathers around the base of their bills that cover the nostrils and act as a bristly filter, keeping out sawdust and tiny wood chips when the birds are excavating cavities.
Other specialized feathers can be found in certain birds, particularly those with crests, otherwise known as the crown at the top of the head. The simple elongation of the feathers of the crown is the most common example of these modified contour feathers. Stellar’s Jay and Pileated Woodpecker each have permanent crests. Some birds, like the kinglets can erect a crest when they become excited or agitated. The Tufted Titmouse has a topknot of feathers at the top of the head. Certain quail, particularly the Gambel’s, California and Mountain Quails have a top-knot unique to each species. The Gambel’s and California have a plume of feathers that somewhat resembles a comma while the Mountain Quail has an elongated plume of feathers that reminds one of an exclamation mark! The “horns” on the Horned Lark are actually two tufts of feathers that suggest horns in their profile. Similarly, the “ears” of some owls species, like screech owls and Long-eared Owls, are actually tufts of feathers.
Rate of Growth
Feathers of juveniles grow rapidly in most species. In passerines, or songbirds, for example, by the time the fledglings leave the nest they are already fully feathered. By 2 to 3 weeks out of the nest, their feathers are fully developed and adult sized. In some game birds, birds of prey, waterfowl, and shore birds – it takes much longer for the down of the chicks to be replaced. The flight feathers of some of our ground-nesting galiform birds grow very rapidly – our quail chicks are able to fly several days after hatching!
Feather Structure and Components
We know that contour feathers make birds waterproof and help keep them warm at the same time. We know that most birds have oil glands at the base of the tail that provide natural oil that birds spread into their feathers as a routine part of their daily sanitary preening rituals. However, it is not the oils that make the feathers waterproof but rather the tightly interlocking structure of the barbed feathers that causes water to run off the bird’s feathers rather than to be absorbed and reach the skin. Remember that familiar expression that ends with “like water off of a duck’s back”. The purpose of the oil preening is to help lubricate feathers and reduce friction between individual feathers, thereby extending the life of the feathers and keeping them in good shape until they are replaced with new ones during their molts. Further, this specialized oil is thought to help keep their feathers cleaner and to rid their feathers of unwanted parasites.
All feathers share the same basic fundamental structure, regardless of their distinctive shapes, colors or functions. The base of each feather is composed of a hollow, bare shaft called the calamus. In historic times, ink pens were initially made from the calamus. (The hollow section could hold a supply of ink and the base end was shaped into a point which allowed the ink to flow onto the paper in a continuous, controlled line). While the feather is growing and alive, blood vessels pass through it. The rachis, or central shaft above the calamus, tapers to a point and helps give the feather its basic structure and stiffness.
Over one thousand small structures, called barbs, extend from both sides of the rachis and become the soft and sometime colorful parts of a feather. Imbedded into the barbs are melanin and carotenoid pigments, among others, that provide the colors we see. Branching off the barbs are over 1000 smaller barbules that lock all the barbs together and make a smooth, uniform surface of contour feathers. The barbules have hooked barbicels at their end that keep the feathers completely interlocked. Taken together, the barbs, barbules and barbicels are called the vane. A single, typical flight feather has over one million tiny parts that fit together precisely to enable proper flight.
Keratin is a strong, lightweight protein found in the basic composition of fingernails, hair, scales, claws, hooves, horns and, yes, feathers. However, feathers contain so many diverse properties that some ornithologists think that feathers are actually superior to fur, fish scales, and even human skin. Growing feathers supply blood, nutrients, and oxygen to the keratin within the feather. If a growing feather is damaged badly or broken off, profuse bleeding will occur. Once the feather is fully grown, the blood supply is cut off and the feather becomes inert or dead.
While keratin gives feathers a basic strength, melanin provides additional “stiffness” and color, especially dark colors such as brown and black. The more melanin, the darker the color and the stiffer the feather. Woodpeckers almost always exhibit considerable black coloration. They expend much energy, drilling holes in wood and prying bark. They use their unusually stiff tail feathers to stay erect and upright while pounding their wood holes in search of insects or excavating cavities. Notice how much black coloration they have, especially in their tails. Their feathers are so stiff that you can hear their feathers clacking as they fly closely overhead or nearby. Goldfinches and most other songbirds sound soft and fluttery, if you hear them at all.
Many birds that have a primarily white coloration, such as American White Pelicans, Snow Geese, and most gulls have black wing tips. Most high-soaring hawks and raptors display similar black markings at the tips of their flight feathers. The extra stiffness that the melanin contains helps reinforce those feathers and prevent them from wearing out prematurely.
Melanin is distributed differently in migrating and non-migrating birds. In migrators, the melanin is more concentrated in the tiny barbs in the smallest parts of the feather, making them stronger and more flexible, but not heavier. In non-migrators, the distribution of melanin is more evenly distributed. Lacking the concentration of melanin in the tips of their flight feathers might also explain why some species molt their feathers more often than others.
Molting and Color Change
Molting is a natural process that happens throughout a bird’s life and is generally thought of as the regular replacement of older, worn feathers with fuller new feathers. Molts occur either annually or semi-annually, depending on the species. The follicles embedded within the bird’s skin determine the feather type, shape, and color. Some birds change colors with the seasons. Raptors, for example, may exhibit darker “morphs” in winter and lighter “morphs” in summer to deal with heating and cooling temperatures. During spring and summer breeding seasons, many colorful songbirds such as yellow goldfinches and blue buntings display their most intense and brilliant colors while those same species coloration becomes more drab and nondescript in the fall and winter non-breeding seasons. Diet and overall nutrition also play a role in the coloration of birds. When their diets are at their nutritional best, their coloration is also at its best. Some species, such as Lesser Sandhill Cranes, spread an iron oxide stain of reddish brown into their feathers while preening after feeding. During their foraging for food in reddish brown mud and earth, their bills get coated with that color and they spread that color into their feathers while they preen later. The color isn’t necessarily permanent, but remains on their feathers for months. This reddish-brown coloration is limited to the parts of the bird’s body that they can reach with their bills while preening.
Non-migrators generally molt once a year. Most backyard birds that are resident in the area fit this category. Locally they include, but are not limited to: Lesser Goldfinches, House Finches, Northern Cardinals, Pyrrhuloxia, Verdin, Cactus Wrens, thrashers, etc. Elsewhere around the country, the familiar resident birds may include chickadees, nuthatches, titmice, crows, sparrows, finches, and others. These resident, non-migrating birds will molt all their body and wing feathers in late summer, after the breeding season and in time for a new coat of feathers for the colder winter. These birds appear the same year around, with no change in color to their new coat of feathers.
If you happen to see, for example, a Northern Cardinal in late summer/early fall during its molt, its appearance may surprise you. Its head may be devoid of red feathers or its body may be blotched with both red and black patches of color. When it loses its older red feathers during its molt, the underlying black skin is now visible and some folks are startled to see this occur, especially for the first time. Within a few weeks the black skin areas will fill in with bright red, almost perfectly shaped feathers and the bird will resume its normal look.
Migrators also molt after their breeding season in what is referred to as a prebasic molt. This change of feathers is for their fall/winter wear, and like most others, results in drab coloration. Their second molt, called the prealternate molt, occurs in late winter and changes the birds back into their most colorful breeding plumage. Ducks are among the many birds that molt twice a year. Adult male Wood Ducks are relatively dull in their off season colors but after their second molt become their most colorful, displaying their good health and virility to females.
Some species lose many or most of their flight feathers, keeping them grounded and flightless for a relatively short period of time. This happens more so with water birds, such as ducks, loons, geese, and Anhingas. The timing of this molt coincides with the time their babies are out of nest but not yet able to fly. This provides for a tighter family unit while this molt occurs.
Juveniles into Adults
Many juvenile birds molt into adult plumage after they are a year old or during their first spring. Some birds, like Bald Eagles, don’t molt into their adult plumage until they are between five and eight years old. Juveniles don’t need to rely on adult plumage until they are fully mature and ready to take a mate and breed. Other young birds, like some woodpeckers, rock doves, and other doves leave the nest as fledglings but have the same coloration and field marks as their adult parents. One way to distinguish which are adults and which are young is to observe their behavior. Most babies will follow and pester the adults to feed them.
Some birds change colors seasonally, such as goldfinches, buntings, and starlings, among others. Their breeding colors return to full intensity after a fall/winter of more dull coloration. Other birds may change seasonally to blend in with their surroundings which may also undergo seasonal changes. Ptarmigans, for example, may exhibit mottled browns, tans, and black to become more camouflaged into their spring/summer breeding habitat. But, when the season changes into winter and snow covers the ground and vegetation, they take on pure white plumage. A still all-white ptarmigan blends into its snowy environment so well that the fox who closely passes by may not ever notice the easy, tasty meal. Their white feathers also scatter the sunlight, warming their bodies and keeping them warm in sub-freezing temperatures.
Another very interesting and unique fact about ptarmigan feathers is that they, and other grouse family members, have evolved two methods of walking on snow that is reminiscent of humans using snowshoes to better aid their ability to traverse on a snowy landscape. Most grouse acquire a fringe of scales along each toe, which enlarges the surface area of the feet. However, the ptarmigan have gone further to increase the surface area of their feet: in their white winter plumage, they develop highly modified dense feathering covering both surfaces of their feet, and their talons become significantly longer. This extra, and unique to them, foot feathering also provides extra insulation against the cold snow. Experiments comparing feathered and plucked ptarmigan feet on soft snow clearly demonstrate that foot feathering eases walking for these birds, like humans using snowshoes. The feathers increase the bearing surface of the foot by about 400% and reduce the distance the foot sinks in snow by roughly 50%!
In most species, the males are usually more brightly colored than their female mates, especially in their breeding season. This arrangement works well for most species as the brightly colored males use their distinctive coloration to attract their mates. And, the duller colored females arouse less notice when they are nesting and caring for eggs and babies. The duller coloration helps keep them inconspicuous, undetected, and less likely to be discovered by predators as a result.
In rare cases, the females may be flashier than the males. A prime example of this is the Belted Kingfisher. Females have an extra “belt” on their chests. This is very uncommon and a rare exception to the “males are more colorful/flashy than their female counterparts”.
Having bold coloration isn’t always an asset. The following example is one you may have observed already in your own backyard. Cooper’s Hawks and, to a lesser degree, Sharp-shinned Hawks disproportionately prey upon male Northern Cardinals, Pyrrhuloxia and grosbeaks by a significant margin. Sometimes, there’s a high price to pay for such colorful and eye-catching plumage.
We’ve all been awestruck when we see such colorful birds as Vermillion Flycatchers, Indigo and Lazuli Buntings, and Summer Tanagers. Yet, birds obtain their colorful plumage in different ways. Melanin is present and universal in mammals and bird species throughout the world. Different types of melanin produce different colors. The most common coloration are the blacks, dark grays, and other dark colors that are produced from eumelanin. Almost all birds have some black and/or gray in their feathers. Black is the absorption of all wavelengths of light/color with no light reflected back to our eyes.
Pheomelanin is more complex. It results in dull shades of yellow, chestnut red, and golden colors. In this case, most of the wavelengths of light are absorbed, with only one, two or three colors reflected back to our eyes.
Melanins, however, are not responsible for producing the brilliant coloration some birds exhibit. The bright red of cardinals, the sunny orange of orioles, and other such colors are the results of carotenoids. They are the second most common class of pigments and reflect bright yellows, reds, and oranges best. Yellow is the most common color, followed by red, followed by orange. And, carotenoids are found throughout a bird’s body, not just in its feathers. This accounts for the orange yolk in the middle of their eggs, bright yellow legs in some species, red in the bills of some birds like ibises, and orange and yellow in the bills of the puffins.
The intensity of color depends on the amount of carotenoids in the feathers. Age, sex, health, and diet all play a role in carotenoid color, saturation, and density. The more densely packed the carotenoids, the brighter the color. Duller colors are due to carotenoids that are scattered throughout the feathers.
Pure white feathers may be lacking pigments but white is also perceived when light enters a feather and all the available sunlight is reflected instead of being absorbed, light is scattered and thereby produce what we perceive as white.
Leucism and Albinism
Some individual birds of any given species may lack the pigmentation that causes coloration. This is known as leucism, or more commonly as partly albino. When the feathers contain only a very small amount of pigmentation, the bird appears mostly white with some noticeable darker markings. This is due to a malfunction in the feather’s production of melanins.
Some birds appear nearly all white, lacking any noticeable color pigmentation. Nearly albino, these birds often have a few feathers with minimal pigmentation, but they may not be obvious. They are sometimes referred to as partial albinos.
Leucism can develop so thoroughly that all the bird’s feathers appear bright white. Birds that are completely lacking in melanin results in a pure albino bird. Pure albinos will not have black colored eyes and legs, but rather pink eyes and legs. This condition is really quite unusual yet can occur in almost any given species throughout the world.
In my lifetime, I have only observed one true albino and two, what I call, near albinos. The true albino was a hummingbird (no idea what species) that was present on Mount Lemmon for a few days, many years ago. It was a big deal in the birding community to see a pure white-feathered, pink-eyed hummingbird in real life. The other sightings, which I called a “near albino”, was an almost purely white-feathered roadrunner and a House Finch.
The roadrunner, seen along the Tanque Verde Wash, had only one gray secondary flight feather on each wing and lacked the pink eyes and legs of a true albino. This roadrunner had black eyes and legs. It was truly startling and unexpected to see this bird. The other such sighting was the House Finch at my feeders in my own backyard in the Tucson Mountains, also quite a few years ago. This finch was covered in pure white feathers but, I remember thinking to myself, it may not have been a true albino because it had a small “mask” of red surrounding the base of its bill. I can’t remember what color its eyes and legs were, so I can’t say it was a true albino. The red mask was very unusual and I don’t ever remember seeing such a thing on a bird before or after, except for the male Pyrrhuloxia. I think it was actually a red stain obtained from foraging on ripe cactus fruit, as I cannot attribute the “red mask” to any other source or origin.
Unfortunately, it is assumed that most albinos live shorten lives as their white coloration stands out in their environment and predators are more likely to notice and prey upon them.
End of Part One