by Margaret Baird
Consider the humble feather: instantly recognizable and
wholly unique to birds, this natural marvel singularly sets
avian species apart from all other earthly creatures. Not only
do feathers make flight possible, they also provide supreme
insulation and camouflage and can even sense motion. Composed
of keratin, the same strong substance that makes up human
fingernails and hair, the feather is by far one of nature's
most astounding feats of design and engineering.
Altogether, the sum of feathers on a bird constitutes its
plumage. While most people are probably familiar with vaned
feathers, which are built around a hollow quill, feathers
actually come in myriad shapes and sizes for an equally wide
variety of functions. Vaned feathers, however, are the most
numerous type of feather on a bird. This group includes the
contour feathers that layer the body as well as the more
prominent and stiff tail and flight feathers that line the
wings.
We've all at one time or another examined a vaned feather
and probably pulled apart the clingy, parallel barbs of the
vane, which are arranged like teeth on a comb. But you'll have
to look at a feather under a magnifying glass or microscope to
see the intricate lattice that weaves the barbs together.
Looking like miniature feathers in their own right, the barbs
have still smaller barbules branching out diagonally from them,
while tiny hooklets lock adjoining barbs together and give
feathers their remarkable strength. The resulting arrangement
looks and works something like a zipper or Velcro and
effectively resists strong winds and repels water and cold.
Underneath the contour feathers are the billowy down
feathers, which have shorter quills and lack hooklets in order
to better capture air and provide insulation. Other specialized
feathers include the minute, hair-like filoplumes, usually
grouped around the contour feathers. The filoplumes are thought
to transmit vibrations or pressure changes to the nervous
system, thereby helping to control flight. Bristles are tactile
feathers—also hair-like—usually found on the head and face.
These are the tiny feathers that screen the nostrils, eyes, and
ear openings from dirt, insects, and other foreign bodies.
Some birds—particularly species like pigeons and herons who
don't possess preen glands—have a curious type of feather
called powder down. These are modified down feathers that
essentially disintegrate into a continuous supply of talc-like,
waxy powder. When dusted over and into the plumage, powder down
functions as an excellent waterproof coating.
Preening
From the human perspective it may look like sheer vanity,
but preening is essential behavior for maintaining plumage in
good working and flying order. Besides serving to clean and
adjust displaced feathers, preening also mends any splits or
tears to feather vanes. By running feathers through their beaks
and gently nibbling, birds can effectively re-hook or "re-zip"
displaced hooklets. Most birds also preen to waterproof their
feathers. Oil is extracted onto the beak from the uropygial or
preen gland, located at the base of the tail, and distributed
onto the feathers, forming an effective shield against the
elements. Since birds obviously can't reach their heads with
their beaks in order to preen, they instead scratch with their
feet to spread oil onto their heads.
However, since an excess of oil can cause the feathers to
become matted and weighed down, birds also include regular
bathing and dusting in their routine feather maintenance. Some
species favor washing the oil off in water while others prefer
fluffing dust onto their feathers to soak up excess oil. You
can help the birds in your sanctuary by providing them with a
dusty area and a water source year-round; install a heater
during the fall and winter months to keep the water
ice-free.
Molting
At least once a year, most birds completely shed or molt
their feathers. This is the process by which worn feathers are
dropped, and new ones grow in their place. Molting generally
occurs after the nesting season, with a new set of feathers
grown in time for the fall migration. Since molting demands a
great deal of energy, having the process take place during a
time when natural food sources are plentiful makes perfect
sense. Most birds molt their feathers gradually and
synchronously, with one side of the body mirroring the other by
shedding corresponding feathers. This steady process allows for
survival—birds can still maintain their balance for flying,
despite the missing feathers. Some species of songbirds even
molt a second time, shedding their drab winter plumage for
breeding finery in early spring.
If you want to appreciate the subtle details and changes in
these remarkable, winged creatures, autumn is the season to
begin restocking your bird feeders. Soon enough you'll probably
see a core group of feeder "regulars" returning again and
again. Keep a sharp eye out: By watching birds from a close
proximity, you'll be able to cultivate a singular appreciation
for the form and function of their feathers.
