ATTENTION:  If you have an older nestling or nestlings that you believe is in
trouble and needs human intervention in order to survive, click

At the Project:
Nestlings continue to develop at an amazing rate.  By day 12 or 13 many actually
outweigh adults!  Their body contour feathers are maturing, and their flight feathers
are rapidly lengthening, though they are still significantly shorter than those of adults.  
And by day 16 their skeletons are nearing adult size.  Your nestlings are starting to
look like proper Tree 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.  Observe boxes from a distance because,
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 that 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 young birds.

How has begging changed as nestlings have grown?
  • A nestling's begging calls can vary, depending on its size and stage of
    development, how hungry or warm it is, and how many nestmates it is
    competing with for food.
  • 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 begging calls of broods 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 often clamber up to and perch in cavity
    entrances, as in the photo below by Liam Gerety.

  • Since access to the interior of the box is frequently blocked now by waiting
    nestlings, adults may simply land briefly at the hole and tip their heads and
    upper bodies in, transfering food without fully entering the box, as in the photo
    below from Francois Paquette.
  • Click here to watch a YouTube video showing how adult swallows fed 13-16
    day old nestlings in Francois Paquette's Quebec nest 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).

  • As fledging approaches adults seem to reduce feeding somewhat.
  • Adult behavior eventually progresses from entering the box to feed young, to
    tipping in to feed young, to feeding young at the hole.  So 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, as you can see for yourself if
    you click here for a YouTube video of older nestlings jockeying for position.
  • On any feeding visit the nestling that is nearest the incoming adult and that
    begs soonest and most vigorously will usually get the food.
  • Nestlings that are temporarily full won't beg, giving others 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 seen below in Steve Byland's photo insures one
    nestling gets everything a parent bringsl on a given visit.

Older nestlings beg very loudly.  Could this have negative consequences?
  • The racket could draw predators.  Perhaps to counter this risk, nestlings 15
    days and older will reduce begging calls and crouch down in their nest if
    parents give alarm calls.
  • 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.
  • The chest muscles that will propel flight are maturing rapidly now, and from
    about day 15 on nestlings start exercising their wings, provided there is room
    inside the cavity.  Holding down firmly with their feet they make short bursts of
    rapid flapping, their wings a blur.
  • Click here for a YouTube video of 15 and 16 day old Tree Swallow nestlings
    fluttering inside Francois Paquette's nest box.
  • Given sufficient room in a box, by the time they must actually fly from the nest
    they will have flapped their wings thousands of times.  This underscores the
    importance of providing boxes with spacious, not cramped, interiors.
  • Other body maintenance behaviors typical of adults, such as preening their now
    quite well-developed feathers, head scratching, and wing stretching also will
    normally have begin by 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 may be fecal debris.

Do adults still remove fecal sacs from late-stage nests?
  • Once older nestlings start blocking entrances, as in the picture below by Bruce
    Vanderveen, it's more and more difficult for adults to access box interiors.
  • Fecal material now accumulates on the floors and up the sides of boxes as
    nestlings try to excrete outside the areas where they sit.
  • 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.  It won't be pretty.

Questions for the next Topic:  Tree Swallow 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?

Older Nestling Development
13 Days to Fledging
Learn About Birds at Tree Swallow Nest Box Projects