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. To watch a YouTube video of Tree Swallows preening click here.
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.
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.
- Feathers trap an insulating layer of air next to the skin, keeping body heat in.
- Feathers form an outer body covering that keeps cold and moisture out, and
which protects a bird's thin skin from abrasions and ultraviolet radiation.
- Feathers help identify members of a species to each other through their
unique colorations and shapes, and their use in species-specific behaviors.
- Feathers are often used in courtship displays and can signal an individual's
health and genetic quality to potential mates.
- Feathers may function to identify individuals within social groups, which can
help maintain dominance hierarchies.
- Feathers can be used in aggressive displays that replace the need for actual
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 in the follicle keratin is extruded out, enlarging the feather.
- When 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 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 is the purpose of all this? How do these behaviors improve feather function
and benefit the bird?
- Zip-up feather barbs that have become separated.
- Return misaligned feathers to their proper place.
- Reincorporate insulating layers of air between feathers.
- Waterproof the feathers.
- 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 bill.
- 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.
- One of the oil's main functions is to waterproof feathers. Notice how
effectively it causes water to bead up and run off in Pete Luedemann's
beautiful photo below of a swallow perched in an Alberta rain.
- Preen oil is also believed to condition feathers, preventing them from
- In addition preen oil may help keep a bird's skin supple, and may possess
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.
- Scratching can also dislodge ectoparasites.
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 systematic replacement of all or portions of a bird's feathers by
new ones. In songbirds molt takes place gradually so they can continue to fly.
- Different songbird species have different timing and patterns of molt, and
some species molt more than once a year.
- 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.
- Because it does demand lots of energy to grow new feathers molt 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. However, Tree Swallows are
exceptions to this rule.
- Adult Tree Swallows have just one complete molt that starts when nestling is
almost over and extends over several months during migration into 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?
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?
Learn About Birds at Tree Swallow Nest Box Projects
|Nesting Guide, Spring Return, Songbird Behavior, Song and Calls, Nest Site Claiming,
Pairing Up, Nest Building, Bird Flight, Mating, Eggs and Egg Laying, Incubation,
Takeovers, Feather Care, Hatching, Nestling Care, Sexing and Aging,
Nestling Growth, Mortality, Older Nestlings, Fledging, Ectoparasites, Juveniles,
Flocks, Migration, Molt, and Winter, Box Care and Project Assessment