Bird feathers come in a variety of sizes, shapes, and colors. These traits reflect the various functions of bird feathers, including protection, warmth, and flight. For the bird enthusiast, feathers also serve as an important way to identify different bird species. Cardinals, for example, can be distinguished from other North American bird species by their bright red plumage.
Unique to birds and their dinosaur ancestors, feathers represent an essential anatomical adaptation made by different bird species to their individual habitats. Feathers represent the bird version of the hair or fur found on mammals such as humans, dogs, and guinea pigs. However, unlike mammalian hair or fur, bird feathers provide more than just a method for thermoregulation. This lesson will examine bird feather anatomy, the different types of feathers, and the functions of these feathers.
Although a feather might look simple in structure to the naked eye, feathers have complex anatomies, which reflect how birds use them. All feathers consist of two main parts, the hard central shaft called the rachis and the softer side branches known as barbs.
At the base of each feather lies a naked portion of the rachis called the calamus or quill. Hundreds of years ago, before the invention of modern ballpoint pens, quills were commonly used as writing implements by dipping the tip of the quill into ink. The calamus, or quill, is the portion of the feather that attaches to a bird's skin or bone and the Rachis extends from the calamus. Each side of the rachis has vanes that form the soft portions of the feather.
The rachis provides support to the feather but must be lightweight to enable flight. As a result, the rachis takes the form of a hollow tube from which the barbs branch off. The barbs, in turn, are connected to one another by barbules that possess hooks called hamuli. The hamuli help to interconnect the network of barbs much like a zipper. Sometimes, the barbules are missing hamuli near the base of the feather. This creates a free-flowing plumage that is less structured than the hooked barbules (with hamuli).
The bird feather diagram below displays the different parts of the bird feather. It is labeled with the calamus (quill), rachis (shaft), barbs, and vane.
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Feathers are classified as pennaceous or plumaceous. Pennaceous feathers contain hooked barbules with hamuli and are more structured and tightly interlocked with one another. Pennaceous feathers are so stiff that they were used as writing utensils hundreds of years ago. By contrast, plumaceous feathers possess barbules lacking hamuli. Plumaceous feathers are more fluffy and less structured than pennaceous feathers.
Aside from these two broad divisions, there are also six main types of feathers found in birds:
These six feather types will be further described below.
Unlike other bird feathers, flight feathers attach directly to the bird's bones. The central rachis of flight feathers is stiff and lined on either side with branching barbs that form flat, aerodynamic vanes. The barbs are connected by hooked barbules possessing hamuli. Flight feathers are long and often asymmetrically shaped, with one vane wider than the other. Flight feathers found on bird wings are called remiges, while those on bird tail feathers are called rectrices. The main function of flight feathers is to support birds' ability to fly.
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Contour feathers are the colorful feathers seen on the outside of a bird. Contour feathers provide colorful plumage, which is useful in identifying different bird species. Contour feathers are part pennaceous and part plumaceous. The portion of the feather farthest from the calamus or quill is highly structured, containing hooked barbules. The region closes to the quill is fluffy and less structured. Contour feathers serve as the first line of defense against temperature, precipitation, and wind.
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Down feathers are soft, fluffy, and smaller in size. Down feathers lack both the rachis and hooked barbules found on other feathers. Located beneath the contour feathers, down feathers provide insulation to the bird.
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In appearance, Semiplume feathers look like a combination of contour and down feathers. Possessing both a rachis and side barbs with smooth barbules, semiplumes are located between the contour feathers and provide the bird with extra insulation. In some bird species, semiplumes are also enlarged and play an important role in the courtship rituals of certain species, such as egrets.
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Filoplume feathers are very small in size, containing a rachis and only a few sparse barbs at the tip. These feathers are located on the underside of the bird's body or on the wings. Filoplumes provide sensory information pertaining to temperature, wind speed, and feather movements needed for birds to fly efficiently.
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Bristle feathers are short and stiff. Located around the eyes and beak of a bird, bristle feathers are also believed to be sensory in nature. Bristles consist of a rachis with a few barbs at the base of the feather.
| Feather type | Description | Barbule | Function |
| Flight | long, stiff, asymmetrical | hooked | flying |
| Contour | colorful, part still, part fluffy | hooked and smooth | protection |
| Down | soft, fluffy, small in size | smooth | insulation |
| Semiplume | cross between contour and down feather | smooth | insulation |
| Filoplume | very small, sparse barbs at tip | smooth | sensory |
| Bristle | short and stiff | smooth | sensory |
As indicated by the different feather types described above, birds use each of these feathers for different functions. Some of these functions will be described below.
Despite being lightweight, flight feathers are both flexible and strong in order to enable birds to fly. Flight feathers are located on the wings and the tail. The wing flight feathers, known as remiges, consist of primary, secondary, and tertiary feathers:
The rectrices, or tail flight feathers, help the bird to maintain stability and control during flight. The tail feathers also provide birds with the ability to land safely by reducing forward velocity.
Both the down and semiplume feathers help to trap air close to the body to keep birds warm in cold weather. The contour feathers on the outside of the body also provide wind and water resistance for the bird. Contour feathers are coated by beta-keratin and a waxy substance which blocks water and allows it to run off of the body. Contour feathers can also possess differences in pigmentation to either absorb or reflect sunlight depending on the habitat in which a bird species is located. Sunlight absorption can help keep birds warm in colder climates, while sunlight reflection can enable birds to stay cooler in warm climates.
Much like a stealth fighter plane, feathers can be used by certain predatory birds, like owls, to muffle the sound of their wings in flight. This enables the owl to approach its prey silently, thus increasing the probability of a successful hunt during the nighttime hours. Some owls also have special facial feathers arranged liked disks that help them hear sounds associated with potential prey.
Other birds can use feather coloring and patterns to help them blend into their environments. By blending into their surroundings, an adaptation which results in camouflage, birds can reduce the chance that a predator will successfully prey upon them.
Some species of birds, such as the crested pigeon of Australia, have specialized flight feathers that produce different tonal pitches to warn other birds of danger. When birds hear this warning alarm, they typically flee as a group to escape potential danger.
Both feather coloration and wing movements can also be used to distract potential rivals or predators. For example,Aposematic coloration is the evolution of bright colors in fur, skin, or feathers to warn animals from attacking the nest and scare away predators. Some bird species will flash conspicuously colorful feathers or feign injury in order to scare or lure away predators from the nest.
Just as feather coloration and patterns can be used to camouflage the bird from potential predators, special colors and patterns can also provide visual cues and signals in mating displays. The beautifully colored feathers of the peacock, for example, serve as a signal of reproductive fitness to females of the same species. Reproductive fitness refers to an individual's ability to pass on genes to the next generation. These colorful feathers are often combined with courtship displays designed to advertise the qualities of a male to his potential mates.
One unusual feather function occurs in bird species living in snow-covered environments; birds, such as grouse, use feathers are snowshoes. These birds have developed feather-covered feet which help to increase the surface area, and thus, prevent the birds from sinking into the snow while walking.
Bird feathers are unique structures comprised of two main parts: the rachis and the barbs. At the base of the rachis is the naked portion of the shaft known as the calamus or quill. On either side of the rachis are vanes made of branching barbs linked together by hooked barbules called hamuli. Feathers can be described as either pennaceous (long and stiff) or plumaceous (soft and fluffy). There are six feather types found in birds:
Bird feathers possess several important functions:
These unique adaptations found in feathers enable birds to occupy habitats not easily accessible to other animal species.
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This activity will help you assess your knowledge of the types and parts of bird feathers.
Complete the crossword by filling in a word that fits each of the given clues. For this activity, you'll need a printer to reproduce the following page. With a pencil and an eraser, neatly write your answers in the boxes provided.
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2. __________ is the flattened, web-like part of a feather, consisting of a series of barbs on either side of the rachis.
4. Barbs themselves are also __________ and form the barbules.
7. The typical feather consists of a central shaft or __________, with countless barbs.
8. The small white feathers that lie between and beneath the __________ feathers are called semiplumes.
10. The primary function of __________ feathers is to aid the bird in thrusting and flying.
1. Bristles are small, stiff feathers typically found on the __________ of most birds.
3. __________ is the lower shaft of a feather, specifically the region lacking barbs.
5. The filoplume is a __________-like feather with a long rachis and just a few barbs on the tip.
6. The loose structure of __________ feathers traps air, which helps to insulate the bird against heat loss.
9. __________ feathers are mainly concerned with stability and control, allowing birds to twist and turn through the air with ease.
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There are six different feather types found in birds. These include: flight feathers, contour feathers, down feathers, semiplumes, filoplumes, and bristle feathers.
Feathers are comprised of two main parts, the rachis and the barbs. The rachis is the stiff central shaft, while the barbs constitute the softer portion of the feather. The barbs are interconnected by hooked barbules called hamuli.
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