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 making 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 dead dry grasses and plant
    stems, or occasionally 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.
  • Both males and females bring feathers.
  • Females do the nest-building, arranging all vegetation and feathers.
  • Females shape the cup, scratching and pushing nest vegetation with their
    breast.
  • Many other songbirds have similar divisions of labor by sex.















What do males do while females gather vegetation?
  • Males often stay at the box guarding it, while females come and go gathering
    vegetation.  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, but research strongly suggests the main purpose of a Tree
Swallow nest's feather lining is to help keep nestlings warm.
  • Feathers could lower heat loss from eggs and young by slowing moving air and
    reducing exposure to moisture.
  • Nestlings in well-feathered nests could use more of their available energy for
    growth and development and less to stay warm.
  • A warmer nest may also let adults spend more time away gathering food.
  • Feathers could help hide eggs and young from predators.
  • Feathers may inhibit ectoparasites in some way.
  • It's possible feathers protect nestlings from being cut or scratched by the ends
    of coarse nest vegetation.
  • Whatever the reason or reasons, Tree Swallow nestlings have been found to
    grow larger and faster, and to survive to fledging more often in nests well-lined
    with feathers, so these feathers are a valuable resource.

















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.
  • If necessary 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.
  • Battles often ensue before one finally is able to get the feather into its nest.  
    Photo below by Euan Reid.

















  • 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.
  • Watch this amazing YouTube video to see how just how eager Tree Swallows
    can be to get white feathers!

Question for the next Topic: Bird Flight.
  • How are birds' bodies different from ours?
  • How are these differences related to a bird's ability to fly?
  • What can't a bird do with its wings?
  • How does a bird change the shape of its wings during flight in order to push
    down a large wing and raise up a small wing?









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Nest Building
Learn About Birds at Tree Swallow Nest Box Projects