At the Project:  
Tree Swallows have been present, claiming boxes and courting for weeks.  
Have you noticed how long it's taken for nest building to start?  Bits of
vegetation appeared in boxes early in site-claiming.  But then there seemed
to be a pause.  However, box checks now reveal nest building has finally
begun in earnest.











Concepts:
Why do birds spend time and energy on nests?  What's a nest's purpose?
  • Nests contain and confine eggs and young in one place.  They keep
    eggs and young from falling out or getting lost.
  • Nest structure clusters eggs and young together for efficient
    incubation and brooding.
  • Nests can protect and insulate eggs and young from wind, cold, and
    damp that could conduct heat away.  

Why did it take Tree Swallows so long to start to build?
  • Tree Swallow arrival, site claiming, and pair formation take place while
    it's still cold.  Many other migrant species won't be back for another
    month or more.  
  • Early arriving swallows won't be laying eggs right away so maybe they
    don't need to hurry to build nests.  (For late-nesters it's a different
    story, as we'll see).

What are Tree Swallow nests made of?  What material do you see in boxes
and see swallows bringing?  Describe a nest.
  • There's usually a base with a cup, both made of old dead plant stems.  
    Some swallows may use pine needles.  Sticks or twigs aren't used.
  • In completed nests feathers, usually white, line and arch over the cup.

Where are the swallows getting their nest vegetation?
  • Most is gathered from the ground within sight of the cavity.






How is the vegetation collected?
  • A swallow flies low, looking down, then drops to the ground.
  • It picks a piece of vegetation in its bill, tugging it loose with flapping
    wings if necessary.
  • Carrying the vegetation in its bill it flies to the nest entrance.
  • Landing at entrance holes with nest material and manipulating it into
    boxes can be difficult.  Large pieces are often dropped.









How do swallows move on the ground as they gather nest material?
  • Awkwardly.  They may flop along using wings for balance.
  • Their legs are very short and not well-adapted for walking or hopping.

What is the sequence of Tree Swallow nest construction?
  • Bits of vegetation appear during box claiming.
  • Slight ring forms around box floor (below left).
  • Ring becomes more obvious as vegetation added (below, left center).
  • Base thickens and cup becomes obvious.  Box bottom may still show
    (below, right center).
  • Feathers, some quite large, are added gradually.
  • Cup completed and feather lining in place (below right).  Some nests
    have many more feathers than the one shown.






Some cups may be in the back middle or back corners rather the center.  
It's suspected some swallows build cups far from entrances for predator
protection.

How long does nest building take once really begun?
  • One to two weeks is average.
  • Feathers are added for several additional weeks.
  • Late season nests may be much skimpier and built in less than a week.

Who builds nests, male, female, or both?
  • Females bring all the plant material.
  • Males bring most feathers, although females may bring some.
  • Females do the building, arranging all vegetation and feathers.
  • Females form the cup by scratching and pushing with their breast.
  • Many birds have similar divisions of labor.

What do males do while females gather vegetation?
  • Males often stay at the box guarding it, or go off foraging.  They don't
    accompany females collecting nest material.
  • Males typically give a soft "Gurgle" call as females bring material and
    while females are inside the box nest building.  It's believed this call
    helps stimulate female nest building and strengthens the pair bond.











What's the purpose of the feathers?
This is a matter of debate.
  • Feathers could cut heat loss from eggs and young by slowing moving air
    and reducing exposure to moisture.
  • They could hide eggs and young from predators.
  • They could inhibit parasites in some way.
  • Whatever the reason, Tree Swallow nestlings appear to grow faster in
    nests well-lined with feathers, so they are a valuable part of nests.

Why are white feathers preferred?
  • We aren't sure.  It's possible they make swallows' white eggs less visible
    to predators.

Where do swallows get the feathers?  Can you identify the bird species the
feathers in your boxes came from?
  • Since swallows often nest in or near wetlands, waterfowl and gulls are
    common feather sources.
  • Tree Swallows will fly several miles to get suitable feathers.

What happens when a swallow arrives carrying a feather?
  • Other swallows may give chase and try to steal it for their own nests.
  • Pursuers call loudly, which may draw a crowd of chasers.







Try bringing white feathers to your project.  Throw some up, and watch the
commotion that follows.  Include a few large ones that require real skill to
carry and maneuver through the entrance hole into the nest.  












Question for the next Topic:  Mating.
DNA studies of Tree Swallows show the nest female is the mother of all the
young in her nest, but the nest male often is not the father of all young in his
nest.  What's going on here?
  • Are some females being forced to copulate with other males, and if so,
    why would males want to do this?
  • Are some females "cheating" on their mates, and if so, why would
    females want to do this?
  • What tactics could a nest male use to assure that he will be the father
    of the young in his nest?

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Nest Building
Learn About Birds at Tree Swallow Nest Box Projects