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?
  • Shortly after hatching nestlings began to give weak, high-pitched peeps.
  • By week two begging calls had become two or three syllable, louder, harsher,
    and lower-pitched.
  • As fledging nears in week three, begging nestlings give rapid, loud chattering
    notes, repeated often.
  • As nestlings age their individual begging calls become more like those of their
    own nestmates, and less like those in other nests.  
  • It's possible these call differences among broods will help parents identify their
    own young for feeding after they have left the nest.

How has adults' feeding of young changed?
  • By the end of two weeks nestlings reach up to entrances.
  • Nest access to the interior of the box 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 without fully entering the box.







  • Still later, as young near fledging, they perch at the hole with heads partly
    out, begging loudly when adults approach.  (Photo below by Greg Page).

















  • Food exchange now becomes so rapid it's hard to see.  Adults perch very
    briefly or flutter in front to make the pass.  (Photo below by Brett Burleigh).


















  • Adults seem to reduce feeding somewhat as fledging approaches.
  • Adult behavior eventually progresses 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 the developmental status of their nestlings.
  • Adults with large young have time for little else but foraging and feeding.

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 soonest and most vigorously will usually be the one 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.
  • The food exchange technique insures one nestling gets all on a given visit!  
    (Photo below by Steve Byland).




















Older nestlings beg very loudly.  Could this have negative consequences?
  • The racket could draw predators.
  • It has been theorized that begging may manipulate parents to forage harder in
    order to quiet nestlings so predators won't be attracted.
  • It has also been suggested that begging displays take a lot of energy to
    produce, but research has shown the energetic cost is actually small.

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 if there is room inside the
    cavity.  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 waxy 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
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