Chapter 4 - Feathers Flashcards
Functions of feathers
. Insulation for regulation of body temperature.
* Aerodynamic power for flight.
* Colors for communication and camouflage.
* Modified feathers may also used for swimming,
sound production, hearing, protection, water
repellency, tactile sensation, etc.
Structure of feathers
Feathers are made of B-keratin, which is a
fibrous protein polymer with strong
mechanical properties.
* The same protein, B-keratin, is also found
in the beaks, claws, and leg scales of
birds.
Structure of Pennaceous Feathers
The vane consists of barbs, which are parallel,
lateral branches of the rachis.
* Each barb consists of a main ramus, which has
many smaller structures, barbules, projecting
from both the proximal and distal surfaces of the
ramus.
* Barbules that project from the proximal surface
of the ramus have a ridge for locking. Barbules
that project from the distal surface of the ramus
have hooks, also known as barbicels.
The hooked barbules from the distal surface of
one barb will hook around the barbules from the
proximal surface of the adjacent barb.
* In this way, the barbs and barbules interlock, like
Velcro, to form the flat but flexible structure of a
pennaceous vane.
Modifications of Vane Structure
In waxwings, the barbs near the distal ends of
some feathers are fused into a wax-like structure
that provides bright coloration
In the Desert Sandgrouse, the
barbules are coiled in a way that
allows them to hold on to extra
water. This species transports
water to its nestlings by dipping its
belly in water and then carrying it
to the nest.
Modifications of Vane Structure In Cormorants and anhingas
In cormorants and anhingas, the loss of
barbicels actually makes the feathers absorb
more water, which helps to reduce buoyancy
during diving. However, these feathers require a
long air drying time.
Modifications of Vane Structure in rails and ducks
the barbs are large and
close together, and the barbicels are extra
long and curved. This causes the feathers
to be more water-repellent.
King Rail
Structure of Plumulaceous Feathers
The loose vanes of
plumulaceous feathers
do have barbs, and
those barbs have
barbules. However, the
barbules do not have
hooks, so they do not
interlock with barbules
on adjacent barbs.
Aftershaft
The contour, or body,
feathers of some bird
have a secondary
structure called an
aftershaft. An aftershaft
consist of another
rachis and vane
attached to the same
calamus.
* Main function is to
enhance insulation.
Flight Feathers
The flight feathers include feathers of the wings (remiges
– provided lift and thrust) and feathers of the tail
(rectrices – used for steering and braking).
* Long, pennaceous feathers designed for aerodynamic
forces during flight.
* Coverts cover the bases of these feathers.
Undertail Coverts
Remiges
divided into primaries and
secondaries. The primaries attach to the bones
of the hand, while the secondaries attach to the
ulna.
The leading edges of remiges are narrow than
the trailing edges; this limits vibrations of the
leading edge.
* This effect is more pronounced on primaries
than on secondaries.
Owl Flight feathers
The rectrices on the feathers of owls have a
modified leading edge. The distal barbs on the
leading edge have very long tips called
pennulae. These create a fuzzy edge on the
surface of the vane that reduces air turbulence
and vibration while in flight. This allows the owls
to have a more silent flight.
American Woodcock flight feathers
Male American Woodcocks due a ritual display
flight to attract mates. Males will spiral upward
into the sky while his wings make twittering
sound produced by air passing through three
narrow outer primaries.
Duck Flight feathers
In many ducks, the secondaries form a
prominent colorful patch called the
speculum.
In the Mandarin Duck, the secondaries are
erected during courtship displays.
What are the rectrices attached to
The rectrices are attached to the
pygostyle.
Tail feathers can be modified in various
ways.
Woodpeckers, Wilsons Snipe, Courtship
Contour feathers
- These are body feathers. They help to define the
outline, or contour, of the bird. - Often pennaceous distally and plumulaceous
proximally (toward the calamus). - Help to streamline the
bird for flight. - May play a major role
in waterproofing.
Down feathers
Short, extremely plumulaceous feathers that has a
weak central rachis (or lacks a rachis altogether).
* Adult (Definitive) Down provides a layer of insulation
under the contour feathers and aids in repelling
water.
* Natal Down, found in hatchlings, serves as the initial
plumage before it is replaced.
Semiplumes
- Similar in shape to a contour feather, but
completely plumulaceous. - Have a distinct rachis.
- Lie underneath the contour feathers to fill gaps;
also help to insulate. - May serve as courtship ornaments.
Powder Down
- Specialized feathers with barbs that disintegrate
into a fine powder. Thought to aid in grooming
and waterproofing. - The only feathers that grow continuously and
are never molted. - Especially prominent in herons.
Filoplumes
- Long, hairlike feathers that
monitor the positions of
pennaceous feathers
(especially the remiges and
rectrices). - Consist of a rachis with a tuft
of barbs near the tip. - Sensory corpuscles in the
follicle of each filoplume detect
fine movements of the shaft.
Bristles
- Specialized feathers that can have sensory or protective
functions. - Consist of a stiff rachis with just a few basal barbs.
- Eyelashes of ostriches, rheas, hornbills, and cuckoos are
bristles. - Located around the mouths of nightjars, where they
collect tactile information.
Feather Coloration
Colors in feathers are due to pigments,
structure, or both.
* Pigments are organic compounds that
absorb the energy of certain wavelengths
of light and reemit the energy of other
wavelengths to produce the observed
colors.
three major types of pigments
- Melanins produce grays, blacks, browns,
and buffy colors. - Carotenoids produce bright yellows,
oranges, and reds (and some purples). - Porphyrins produce reddish-brown colors
and, in some African birds, olive-green and
magenta.
Melanins
Nearly all feathers have some melanin in them.
* Synthesized in melanocytes in the skin from the amino
acid tyrosine.
* The melanin is packaged into melanosomes, which are
then transferred into developing feathers.
* Pigmentation patterns with feathers are due to temporal
variations in the transfer or melanosomes.
Two Kinds of Melanin
Eumelanin (blacks
and grays) and Pheomelanin (reddish-
brown, buffy-tan, and rufous colors).
Melanins have multiple functions (other
than imparting color)
- Increase resistance to stress and wear.
- Increase resistance to degradation by
feather-eating bacteria. Some bacteria
secrete an enzyme that breaks down b-
keratin. Increased levels of melanin reduce
this damage. - Absorb radiant energy. This may help with
thermoregulation.
Carotenoids
- Originally produced by plants and derived
by diet. - Thirty-nine different carotenoid molecules
have been identified in feathers. - The reds, oranges and yellows of parrots
come from a different class of pigments
known as psittacofulvins (not derived from
diet).
Porphyrins
Ring-shaped molecules similar to
hemoglobin and chlorophyll in structure.
* Causes magenta and bright olive-green
coloration in turacos.
Structural Colors
- Includes blues, some reds, some greens,
and iridescence. - Color is produced when light waves
bounce off the interfaces of nanometer-
scale structures in the feather.
Three different classes of structural feathers
- White - Random reflectance of all visible
wavelengths produces white when light scatters off
cellular air bubbles. For example, the Rock
Ptarmigan is white due to extra large air bubbles in
the barbules, which magnifies the amount of light
reflected. - Iridescence - Reflectance of wavelengths
from layers or arrays of melanosomes in the
barbules. This produces iridescence (a
change in hue dependent upon the angle of
illumination or observation). The color
produced depends on the size of the
melanosomes and how they are arranged. - Non-iridescent Colors – Produced by
reflectance of wavelengths off air bubbles
within cells of the rami of the feather barbs.
The same wavelengths are backscattered
regardless of the angle of incidence or
observation. Smaller bubbles produce bluer
colors, while larger bubbles produce greener
colors
Ultraviolet Colors
The blue and violet colors of birds are often also rich in
ultraviolet (UV) reflectance.
* Humans cannot see UV wavelengths, but most birds
can.
* All avian families exhibit this trait.
The Plumage
- The entire plumage consists of thousands
of feathers. - Tundra Swan = 25,000 feathers
- Most Songbirds = 2,000 – 4,000 feathers
- The feathers weigh 15-20% of the total
body mass.
Pterylae vs Apteria
he pterylae include numerous feather placodes which each develop into a feather follicle. Each follicle grows a series of feathers, which are replaced over time by periodic molts. Apteria are spaces between pterylae which lack contour feathers or which lack feathers entirely.
Feather Care
Birds preen their feathers with their beaks and toes
to maintain their pennaceous feather vanes and to
remove parasites (mites, lice, bacteria, etc.)
* Birds also apply a waxy secretion from the uropygial
gland (preen gland), which is located on the rump.
This preserves feather moistness and flexibility and
helps to waterproof the feathers.
* Some birds have miniature combs on the inner
margins of their middle claws.
* Allopreening
Molt
Alternate plumage throughout life
Sexual Dimorphism
Many species are sexually dimorphic
