Feathers developed from the scales of reptiles, and set birds different from all other species. Flight, insulation, and courting displays all need feathers. Colors and forms of feathers help us identify between various bird species and, in certain circumstances, between males and females. Because feathers are so unique, there are several anatomical and technical names used to describe them. This article will help you acquire some of the terminology and have a better understanding of these extraordinary adaptations.
Keratin, the same protein found in hair and nails, is used to make feathers. A central shaft runs across feathers.
The calamus is the smooth, unpigmented foundation that extends under the skin into the feather follicle. The rachis or scapus is the area above the skin from which the smaller barbs or branches protrude.
Each side of the rachis has a pair of filaments called barbs that come off at around a 45o angle. The vane is the barb-covered section of the feather. These barbs contain two sets of tiny filaments called barbules in the bigger feathers. Barbules from one barb overlap the barbules of the next barbs at a 90o angle. Barbules, in turn, contain hooklets, often termed hamuli or barbicels, which hook the barbules together, like a zipper, providing a tight, smooth surface. These help to keep the form of the feather. The feather would not be able to survive air resistance during flight without these strong links. If the barbs or hooklets get separated from one another, the bird may rejoin them when preening. There are often barbs at the base of the feathers that are not connected together. These are known as downy barbs.
Feathers containing barbules and hooklets are called “pennaceous,” and they are similar to the feathers used in quill pens. Down feathers, for example, are termed “plumaceous” because they lack barbules and hooklets and have the appearance of a plume.
Some feathers have both pennaceous and plumaceous segments. Some feathers feature afterfeathers, or hypopenae, near the base of the vane in a region known as the distal umbilicus.
These are essentially barbs without hooks that assist trap air and provide some insulation.
The feathers of the bird are not organised randomly, but in big identifiable tracts called pterylae. Apterylae are the featherless patches between the pterylae.
Types of Feathers
As there are many forms of hair on furred animals, birds have different kinds of feathers, each having a distinct role. Feathers come in many varieties, including:
- Feathers with Vanes: Contour and Flight Feathers
Contour feathers: Contour feathers cover the majority of the bird’s surface, giving it a smooth look. They protect the bird from sun, wind, rain, and harm. Often, these feathers are brilliantly coloured and have distinct colour patterns. Contour feathers are classified as either flying feathers or body feathers.
Feathers for flight: The term “flight” refers to the flight of a huge bird. The remiges are the flight feathers of the wing that are divided into three groups.
The primaries are responsible for forward thrust and are attached to the metacarpal (wrist) and phalangeal (finger) bones at the far end of the wing. There are typically ten primaries, which are numbered from the inside out.
The secondaries are attached to the ulna, a bone in the centre of the wing, and provide “lift.” They are often utilised in wooing ceremonies. There are normally 10-14 secondaries and they are numbered from the outside in.
Tertiaries are flying feathers that are closest to the body.
The tail feathers, known as retrices, operate as brakes and rudders, regulating flight direction. The majority of birds have 12 tail feathers.
Coverts are tiny contour feathers that cover the bases of the flying feathers. The wing has numerous layers of coverts. Coverts conceal the ear as well.
Feathers on the ground: Down feathers are tiny, soft, and fluffy feathers located under the contour feathers. They are plumaceous, with numerous non-interlocking barbs but no barbules or hooklets like contour and flying feathers.
This allows them to trap air in an insulating layer near to the skin, keeping the bird warm and cold. Because they are so effective, people employ them for insulation in down coats and comforters.
Powder down feathers are a unique form of downy feather. When the sheaths or barbs of these feathers dissolve, they generate a fine keratin powder, which the bird may use to waterproof its feathers. As the bird preens, the powder also aids in cleaning. In birds such as cockatoos and African greys, the lack of powder down may be an indication of sickness, including beak and feather disease.
Filoplumes are delicate, hair-like feathers with a long shaft and just a few barbs at the tips. They run the length of the pyterlae. Although their function is unknown, it is believed that they provide a sensory role, potentially by altering the position of the flying feathers in reaction to air pressure.
Semiplumes give shape, aerodynamics, and insulation. They are often used in courting displays. They have a big rachis, but their vanes are loose (plumaceous). They may occur in conjunction with contour feathers or as distinct pterylae.
Bristle feathers feature a strong rachis with just a few barbs near the base. They are most often seen on the head (around the eyelids, nares, and mouth). They are supposed to have a sensory as well as a defensive function.
Feathers, like hair, grow in a specific part of the skin called a follicle. As a new feather grows, an artery and vein stretch up into the shaft, nourishing the feather. A blood feather is a feather in this stage. The shaft of a blood feather appears black due to the colour of the blood supply, but the shaft of an older, mature feather appears white. The quill (calamus) of a blood feather is bigger than that of a mature feather. A blood feather begins with a waxy keratin coating that protects it as it develops. When the feather matures, the blood supply diminishes and the waxy coating is shed by the bird.
Although an adult bird will usually replace all of its feathers during a moult, the feather loss is staggered, frequently over many months, to ensure that the bird has enough feathers for flight and insulation. A moult is primarily prompted by a change in day length, however it may also happen after breeding. Some wild birds, such as goldfinches, moult twice a year and go from a colourful plumage during the mating season to a more melancholy plumage the rest of the year.
The presence of pigments like as melanins, carotenoids, and porphyrins determines the colour of feathers.
- Melanins are pigments that range from brown to black and are present in animals. Melanins, in addition to imparting colour to the feather, make it denser and more resistant to wear and breakdown caused by sunshine.
- Carotenoids have a yellow, orange, or red tint. They are produced in plants, ingested by the bird’s digestive system, and then taken up by the follicle cells as the feather develops.
- The pigments in the feathers are derived from the pigments in the feathers.
The next time you look at a bird, you’ll have a better understanding of how its feathers protect it and allow it to fly. You can see the intricacy and specialisation that make birds such a unique component of the animal world down to the smallest level.
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