At the Project:
Unless you have takeover attempts in progress it may seem a bit quiet now.  Most
females are spending large amounts of time inside boxes incubating their precious
eggs.  When males are present they perch on or near their box keeping watch and
singing at the occasional intruder.  And when nothing else appears to be happening
they often preen their feathers.  Although this may seem like a "leisure time
activity", it's anything but unimportant.  Caring for feathers is absolutely vital for the
health and survival of songbirds, especially for swallows, one of the most aerial
groups of birds.












Since swallows perch as they maintain their feathers, the apparent calm of the
incubation period is a time when you might want to bring binoculars so you can
observe feather care close up.













Concepts:
Feathers are truly marvelous things.  Note the stiff central shaft or "rachis", on the
swallow wing feathers below, and the two "vanes" that protrude from opposite sides
of the shaft.  Each vane is composed in turn of many smaller "barbs" aligned in parallel
rows.  What you can't see are the tiny hook-like "barbules" on each barb that
interlock with barbules on adjacent barbs, holding the barbs together like velcro.  
The picture shows a few barbs whose barbules have become unzipped.














If you have access to a good microscope remove a feather from a nest lining for a
magnified examination.  You'll be amazed at its intricacy.  

Why are feathers so important to a bird?  Why must they be cared for?
Feathers:
  • Are a bird's flight surfaces.  They streamline, propel, steer, and balance a bird's
    body for efficient aerodynamic passage through the air.
  • Trap an insulating layer of air next to the skin, keeping body heat in.
  • Form an outer body covering that keeps cold and moisture out, and protects a
    bird's thin skin from abrasions and ultraviolet radiation.
  • Help identify members of a species to each other through their unique
    colorations and shapes, and their use in species-specific behaviors.
  • Are often used in courtship displays and can indicate an individual's health and
    genetic quality to potential mates.
  • May function to identify individuals within social groups, helping to maintain
    dominance hierarchies.
  • Can be used in aggressive displays that replace the need for actual fighting.












What are feathers made of?
  • Feathers are mostly composed of keratin, a tough but flexible protein.
  • Bird claws and outer beak coverings are also made of keratin.  
  • Your own hair and fingernails are made of a slightly different form of keratin.

Are feathers alive?
  • No, feathers are dead tissue.
  • Feathers are produced by living cells located in small pit-like follicles in a bird's
    epidermis, its outer skin layer.  
  • As it's produced keratin is protruded straight out from the skin follicle,
    enlarging the feather.
  • As soon a feather has reached its full size the blood supply to the base of the
    feather shaft is cut off and the shaft base stiffens.  The feather is now a fully
    functional, but non-living, structure.

How do birds care for their feathers?
You should be able to see your Tree Swallows:
  • Grasp feathers and draw them through their bills one at a time.
  • Straighten and arrange their feathers with their bills.
  • Fluff their feathers up with a shivering shake of their body.
  • Spread each wing out over their raised legs one by one.
  • Stretch their wings simultaneously up and over their heads.












What does all this do for the feathers?
These actions:
  • "Zip-up" feather barbs that have become separated.
  • Return misaligned feathers to their proper place.
  • Reincorporate insulating layers of air between feathers.
  • Help remove dirt and debris.
  • Dislodge ectoparasites.

You may have heard that birds have a "preen gland".  What is this?
  • A bird's "preen gland" or "uropygial gland" is a pimple-like structure on its
    rump.  It's easiest seen in nestlings, like the seven day old below.







  • The preen gland secretes an oil when it is pressed by a bird's beak.
  • The oil can then be spread onto feathers as the bird draws them through its
    bill one by one.
  • You should see swallows reach back and touch their rump with their bill to get
    oil as they preen.  
  • It was once thought the oil helped waterproof feathers, but now it's believed
    the oil acts mainly as a conditioner that prevents feathers from becoming
    brittle and keeps skin supple.  It may also have antibacterial and antifungal
    properties.

Why do swallows scratch their heads and necks with their feet?
  • They can't reach some feathers with their bill so they use their foot to transfer
    preen gland oil to hard to reach spots.











Don't feathers wear out eventually?
  • Yes they do, in spite of all this care.  Considering the constant use and wear
    these thin, light, seemingly delicate structures are subjected to it's amazing
    they last as long as they do, but eventually birds must "molt".
  • Molting is the gradual and systematic replacement of all or portions of a bird's
    feathers by new ones.  
  • Different songbird species have different timing and patterns of molts, and
    some species molt more than once a year.
  • Molting usually occurs when nothing else major is going on in a bird's life, for
    instance, before or after nesting, or before or after migration.
  • Adult Tree Swallows have just one complete molt that starts when nestling is
    almost over and extends gradually over several months into the autumn.  
  • Many other songbirds have a complete molt after nesting plus a partial molt
    before the following nesting season begins.
  • Juvenile Tree Swallows also have a complete molt that starts soon after they
    fledge.  By October or November young males will have attained the AHY
    plumage they will retain all their lives and young females their distinctive SY
    plumage.  (See Sexing and Aging for more on this subject).
  • The photo below by Jeremiah Trimble shows a molting juvenile Tree Swallow in
    late August.  Note how its faded brownish juvenile feathers have been partly
    replaced by darker adult ones.  Can you tell how we know this bird is a male?

















  • Molting is "expensive" for songbirds.  Replacing old feathers with new requires
    lots of raw materials and energy, plus it's harder to fly and keep warm with
    some feathers missing or only partly regrown.

What happens if a feather is damaged or lost before molting season?
  • If a whole feather is pulled out or lost, a new one will begin to grow at once.
  • But if a feather is only damaged or partly broken off, it will not be replaced
    until scheduled molt.

What other parts of their body exteriors do songbirds need to care for?
  • You are bound to see your swallows performing other maintenance behaviors
    besides feather care.
  • Watch for bill wiping (below) and foot picking.












Questions for the next Topic:  Hatching.
What do you think newly-hatched young swallows are going to look like?
  • Lots of feathers or few?
  • Eyes open or closed?
  • Able to walk or unable?
  • Will they be able they move at all?
  • Will they be nearly independent or helpless?
  • What do you think the young will need to be able to do at hatching?








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Feather Care
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