Everything about Feather totally explained
Feathers are one of the epidermal growths that form the distinctive outer covering, or
plumage, on
birds. They are the outstanding characteristic that distinguishes the Class
Aves from all other living groups. Other
Theropoda also had feathers (see
Feathered dinosaurs).
Characteristics
Feathers are among the most complex structural organs found in
vertebrates:
integumentary
appendages, formed by controlled proliferation of
cells in the
epidermis, or outer skin layer, that produce
keratin proteins. The β-keratins in feathers,
beaks and claws — and the
claws,
scales and
shells of
reptiles — are composed of protein strands
hydrogen-bonded into
β-pleated sheets, which are then further twisted and
crosslinked by
disulfide bridges into structures even tougher than the α-keratins of mammalian
hair,
horns and
hoof.
Feathers insulate birds from water and cold temperatures. The individual feathers in the wings and tail play important roles in controlling flight. These have their own identity and are not just randomly distributed. Some species have a
crest of feathers on their heads. Although feathers are light, a bird's plumage weighs two or three times more than its skeleton, since many bones are hollow and contain air sacs. Color patterns serve as
camouflage against
predators for birds in their habitats, and by predators looking for a meal. As with fish, the top and bottom colors may be different to provide camouflage during flight. Striking differences in feather patterns and colors are part of the
sexual dimorphism of many bird species and are particularly important in selection of mating pairs. The remarkable colors and feather sizes of some species have never been fully explained.
There are two basic types of feather:
vaned feathers which cover the exterior of the body, and
down feathers which are underneath the vaned feathers. The
pennaceous feathers are vaned feathers. Also called
contour feathers, pennaceous feathers are distributed over the whole body. Some of them are modified into remiges, the
flight feathers of the wing, and rectrices, the flight feathers of the tail. A typical vaned feather features a main shaft, called the
rachis. Fused to the rachis are a series of branches, or
barbs; the
barbs themselves are also branched and form the
barbules. These barbules have minute hooks called
barbicels for cross-attachment. Down feathers are fluffy because they lack barbicels, so the barbules float free of each other, allowing the down to trap much air and provide excellent thermal insulation. At the base of the feather, the rachis expands to form the hollow tubular
calamus, or
quill, which inserts into a
follicle in the
skin.
The
Dyck texture is what causes the colors blue and green in most parrots. This is due to a texture effect in microscopic portions of the feather itself, rather than pigment, or the
Tyndall effect as was previously believed. The Dyck texture alters color produced by pigment. Thus, an albino parrot will be white. The spectacular red feathers of certain parrots owe their vibrancy to a rare set of pigments found nowhere else in nature.
Albinism is a rare lack of pigment in some or all of a bird's feathers.
In some birds, the feather colors may be created or altered by uropygial gland secretions. The yellow bill colors of many hornbills are produced by preen gland secretions. Other differences that may only be visible in the ultraviolet region are also possible.
A bird's feathers are replaced periodically during its life through
molting. New feathers are formed through the same follicle from which the old ones were fledged.
Some birds have a supply of
powder down feathers which grow continuously, with small particles regularly breaking off from the ends of the barbules. These particles produce a
powder that sifts through the feathers on the bird's body and acts as a waterproofing agent and a feather
conditioner. Powder down has evolved independently in several taxa and can be found in down as well as pennaceous feathers. They may be scattered in plumage in the pigeons and parrots or in localized patches on the breast, belly or flanks as in herons and frogmouths. Herons use their bill to break the feathers and to spread them while cockatoos may use their head as a powder puff to apply the powder. In one study, Willow Flycatchers (
Empidonax traillii) and they were found to catch insects equally well before and after removal of the rictal bristles.
Feathers are not uniformly distributed on the skin of the bird except in the
Penguin. In most birds the feathers grow from specific tracts of skin called pterylae while there are regions which are free of feathers called apterylae. The arrangement of these feather tracts, pterylosis, varies across bird families.
Evolution
Feathers most likely originated as a filamentous insulation structure, or possibly as markers for mating, with flight emerging only as a secondary purpose. It has been thought that feathers evolved from the
scales of
reptiles, but recent research suggests that while there's a definite relationship between these structures, it remains uncertain of the exact process. (see
Quarterly Review of Biology 77:3 (September 2002): 261-95). In experiments where a virus was used to reduce the levels of certain proteins in chicken embryos, the chickens retained webbed feet, and the
scutes developed into feathers. The scales, however, didn't develop into feathers, and the research suggests that feathers didn't evolve from reptilian scales.
Feathered dinosaurs
Several
dinosaurs have been discovered with feathers on their limbs that wouldn't have functioned for flight. One theory is that feathers originally developed on dinosaurs as a means of
insulation; those small dinosaurs that then grew longer feathers may have found them helpful in gliding, which would have begun the evolutionary process that resulted in some proto-birds like
Archaeopteryx and
Microraptor zhaoianus. Other dinosaurs discovered with feathers include
Pedopenna daohugouensis,
Sinosauropteryx, and
Dilong paradoxus, a
tyrannosauroid which is 60 to 70 million years older than
Tyrannosaurus rex. Currently the question isn't whether birds are dinosaurs, but whether they're
deinonychosaurians or are
dromaeosaurids. It has been suggested that
Pedopenna is older than
Archaeopteryx, however, their age remains doubted by some experts.
Human uses
Feathers have a number of utilitarian and cultural and religious uses.
Utilitarian functions
Feathers are both soft and excellent at trapping
heat; thus, they're sometimes used in high-class
bedding, especially
pillows,
blankets, and
mattresses. They are also used as filling for winter
clothing, such as quilted
coats and
sleeping bags;
goose down especially has great
loft, the ability to expand from a compressed, stored state to trap large amounts of compartmentalized, insulating air. Bird feathers have long been used for
fletching arrows and in the past were used for ink pens. Colorful feathers such as those belonging to
pheasants have been used to decorate
fishing lures and
hats. During the 18th, 19th, and even 20th Centuries a booming international trade in plumes, to satisfy market demand in North America and Europe for extravagant
head-dresses as adornment for fashionable women, caused so much destruction (for example, to
egret breeding colonies) that a major campaign against it by conservationists caused the fashion to change and the market to collapse.
Feathers of large birds (most often
geese) have been and are used to make
quill pens. The word
pen itself is derived from the Latin
penna for feather. The French
nom-de-plume for
pen name has a similar origin.
Cultural and religious uses
Eagle feathers have great
cultural and
spiritual value to
American Indians in the
USA and
First Nations peoples in
Canada as religious objects. In the United States the
religious use of
eagle and
hawk feathers are governed by the
eagle feather law (50 CFR 22), a federal law limiting the possession of eagle feathers to certified and enrolled members of federally recognized Native American tribes.
Various birds and their plumages serve as cultural icons throughout the world, from the hawk in ancient Egypt to the bald eagle and the turkey in the United States. In
Greek mythology, Daedelus the inventor and
Icarus tried to escape his prison by attaching feathered wings to his shoulders with wax, which was melted by the Sun.
Further Information
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