At the Project:
Nestlings continue to grow at an amazing rate.  Many actually outweigh adults
temporarily!  Body contour feathers are filling out.  Flight feathers lengthen,
although they are still significantly shorter than adults'.  Nestlings are starting
to look like proper swallows and their behavior shows they will fledge soon.












Warning!!!  Do NOT check any boxes where nestlings are over 12 days!!!  
Don't go anywhere near them if you can avoid it.  If startled older nestlings
may leap out of the box and try to fly before their flight feathers and muscles
are ready.  If you return them to the box they usually jump back out again.
Nestlings that try to fledge prematurely usually die.  (The picture above of a
15 day nestling was taken before we understood the dangers involved).

Take a close look at the 12 day nestling's wing, below.  Notice how the flight
feathers have partly erupted from their sheaths, so they look like little
paintbrushes.  If you find nestlings in a box have flight feathers more
erupted than these, leave them alone!  Handling them for any reason, even
banding, risks premature fledging and the death of the birds.












Concepts:
How has begging changed as nestlings have grown?
  • Toward the end of week one nestlings began to give weak, high-
    pitched peeps.
  • In week two begging calls became two or three syllable, louder,
    harsher, and lower-pitched.
  • As fledging nears in week three, begging nestlings give rapid, loud
    chattering notes, repeated often.

How has adults' feeding of young changed?
  • By the end of two weeks nestlings reach up to entrances.
  • Nest access is now often blocked by waiting nestlings, so adults may
    simply perch at the hole and tip their heads and upper bodies in to
    transfer food.







  • Still later, as young get close to fledging, they perch at the hole with
    heads partly out.  Food exchange becomes so rapid it's hard to see.  
    Adults perch very briefly or flutter in front to make the pass.









  • Adults seem to reduce feeding as fledging approaches.
  • Adult behavior has progressed from entering the box to feed young, to
    tipping in to feed young, to feeding young at the hole.  Watching
    adults can give you clues to developmental status of their nestlings.
  • Adults now have time for little but foraging and feeding young.

Do young compete for food?
  • They do compete with their brothers and sisters, and it's truly a life
    and death struggle.
  • On any feeding visit the nestling that is nearest the incoming adult and
    that begs most vigorously will be fed.
  • Nestlings that are temporarily full won't beg, giving others have a
    chance to be fed.
  • If food is scarce, all young are constantly hungry and beg whenever
    adults arrive.  The least effective will starve and die unless the
    shortage eases.
  • Adults won't feed unresponsive (non-begging) nestlings.
  • Stronger late-stage nestlings can monopolize the entrance hole,
    preventing those inside from reaching food.







Older nestlings beg loudly.  Could this have negative consequences?
  • The racket could draw predators.
  • It has been suggested that begging manipulates parents to forage
    harder in order to quiet nestlings so predators won't be attracted.

What other behavior changes do older nestlings show?
  • As you would expect older nestlings begin to exhibit adult-like
    behaviors.
  • By about day 15 they start exercising their wings.  Standing in one
    place they make short bursts of rapid flapping, their wings a blur.  
  • By the time they must actually fly from the nest for the first time they
    will have flapped their wings thousands of times.  This underscores the
    value of providing boxes with spacious, not cramped, interiors.
  • Other body maintenance behaviors typical of adults, such as preening
    of their now quite well-developed feathers, head scratching, and wing
    stretching also begin about day 15.

What are the flecks of white powder on older nestlings and in the boxes?
  • Most is feather sheath material that disintegrates as feathers erupt and
    nestlings preen.
  • Some is fecal debris.

Do adults still remove fecal sacs from late-stage nests?
  • Young start blocking entrances by about day 15, so adults have little
    access to the interior.
  • Feces stop being encased in sacs about this time, so there aren't any
    sacs for adults to remove.
  • As a result what do you think nests look like now?  (You'll see when you
    open the boxes after you're certain the young have fledged).

Questions for the next Topic:  Fledging.
  • What is "fledging"?
  • What must Tree Swallow nestlings be able to do when they leave the
    nest?
  • Do you think parent Tree Swallows will care for their young after they
    fledge?  If so, in what way and for how long?

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Older Nestlings
Learn About Birds at Tree Swallow Nest Box Projects