Encyclopedia
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 .
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 ß-keratins in feathers,
beaks and claws — and the claws, scales and
shells of
reptiles — are composed of protein strands
hydrogen-bonded into
ß-pleated sheats, which are then further twisted and
crosslinked by disulfide bridges into structures even tougher than the a-keratins of mammalian
hair, horns and hoof.
Feathers insulate birds from water and cold temperatures. 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 colours 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 colours 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.
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. Most
waterbirds produce a large amount of powder down. Waterproofing can be lost by exposure to
emulsifying agents due to human
pollution. Feathers can become waterlogged and birds may sink. It is also very difficult to clean and rescue birds whose feathers have been fouled by
oil spills.
Bristles are stiff, tapering feathers with a large rachis but few barbs.
Rictal bristles are bristles found around the eyes and bill. They serve a similar purpose to
eyelashes and
vibrissae in mammals.
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 is a definite relationship between these structures, it remains uncertain the exact process. . Experiments show that the same protein that causes bird feet to stay webbed, causes bird scutes and scales to become feathers.
Feathered dinosaurs
Although birds use feathers primarily for flight, several
dinosaurs have been discovered with feathers on their limbs that would not 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 , from the Late Jurassic [i] Period [i] of what is now Germany [i], is the ear...
and
Microraptor was a genus of small, dromaeosaurid [i] dinosaur [i] from the Lower Cretaceous [i] Period [i] ...
zhaoianus. Other dinosaurs discovered with feathers include
Pedopenna daohugouensis,
Sinosauropteryx is the first and most primitive dinosaur [i] found with the fossilized impressions o ...
, and
Dilong paradoxus is a small, feathered [i] tyrannosaurid [i] dinosaur [i] ...
. Currently the question is whether birds are deinonychosaurians or
dromaeosaurids, not whether birds are dinosaurs. It has been suggested that
Pedopenna is older than
Archaeopteryx, however, their age remains doubted by some experts.
Dilong is a tyrannosauroid which predates
Tyrannosaurus rex is a genus [i] of tyrannosaurid [i] theropod [i] dinosaur [i]. ...
by 60 to 70 million years.
Human uses
Feathers have a number of utilitarian and cultural and religious uses.
Utilitarian FunctionsFeathers are both soft and excellent at trapping
heat; thus, they are 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. They have also been put to use as
sexual aids; see feather-dancing. Another human use is
tickling for their soft feeling. Colorful feathers such as those belonging to
pheasants have been used in the past to decorate
hats and
fishing lures. During the late 19th and early 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 that a major campaign against it by conservationists caused the fashion to change and the market to collapse.
Cultural and Religious UsesEagle feathers have great
cultural and spiritual value to
American Indians as religious objects. The
religious use of
eagle and
hawk feathers are governed by the eagle feather law , a federal law limiting the possession of
eagle feathers to certified and enrolled members of federally-recornized
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, Icarus tried to escape his prison by attaching feathered wings to his shoulders with wax, which melted near the Sun.
See also
- Pinion
- Pinioning
- Eagle feather law
References
DeMeo, Antonia M.
Access to Eagles and Eagle Parts: Environmental Protection v. Native American Free Exercise of ReligionElectronic Code of Federal Regulations ,
Title 50: Wildlife and Fisheries PART 22—EAGLE PERMITSStokes, DaShanne.
U.S. v. Thirty Eight Golden Eagles
External links
