Why do Tree Swallows use nest boxes?
Cavity-nesting birds like Tree Swallows, that can't make their own cavities,
usually face a shortage of nest sites.  Competition for cavities can be intense,
even a matter of life and death, since failing to reproduce is a critical failure
for short-lived songbirds.  Tree Swallows must compete for nest sites with
other Tree Swallows and also with other cavity-nesters like bluebirds, wrens,
starlings and house sparrows.  Since natural cavities are scarce Tree Swallows
quickly accept nest boxes, and they aren't picky!  They'll use just about any
box they can get into.  Their nests have been found in large houses for Purple
Martins, Wood Ducks and Screech Owls, and in such unlikely spots as drain
pipes, mailboxes and newspaper tubes (see the photo below by Laura Niang).  
Sadly, they'll also try to nest in unsuitable tiny or flimsy boxes where few if
any young survive.















Be sure to build boxes designed specifically for Tree Swallows.
You'll want boxes like the one below, boxes built carefully of good materials,
where your swallows will be safe from predators and protected from rain and
heat, ones roomy enough so parent swallows can raise strong, healthy young.

For a good Tree Swallow box plan click here:  BOX DESIGN.  
This connects you to the Golondrinas de las Americas (Swallows of the
Americas) web site run by Cornell University.  The Golondrinas project  
promotes and coordinates ornithological research into the biology, ecology,
and behavior of Tree Swallows and the eight other species in genus
Tachycineta.  Their box design is being used for the thousands of boxes
operated by Golondrinas scientists at research sites throughout North and
South America (see map).










All Tree Swallow boxes should have:
  • Sturdy wood construction using 1" rough-cut boards or exterior-grade
    plywood at least 1/2" thick.
  • 1 3/8" to 1 1/2" entrance holes to keep larger birds out.
  • Entrance holes centered about 7" above floors.
  • Floors no smaller than 5" x 5".
  • Roofs that slope down and overlap sides and fronts, reducing exposure
    to rain and predators.
  • Sides that swing open for easy checking of box contents and cleaning.
  • Air holes in upper sides for ventilation.
  • Floor holes for drainage.
  • Floors recessed to minimize interior wetness.
  • Unpainted interiors.
  • Roughened or grooved front interiors to provide nestling footholds.
  • No outside perches at the entrance holes that could aid predators.  

WARNING!!!  DON'T MAKE YOUR BOXES TOO SMALL!  Many published box
plans are intended for bluebirds, which average fewer nestlings per brood
than swallows.  Bluebird designs often have interior dimensions that are far
too small for swallow broods of up to seven young.  You may meet bluebird
hobbyists who say these smaller bluebird boxes are just fine for swallows.  
They are NOT!  While it is true that Tree Swallows will accept small boxes due
to a shortage of nest cavities, their nestlings may not all thrive or fledge
successfully.  Boxes with small internal volumes can put nestlings at risk of
death from hyperthermia (overheating) during hot spells.  Smaller nestlings
may get trampled by their siblings, have their feathers soiled with feces, and
be unable to reach food brought by parents.  Swallow nestlings also require
space to exercise their wings so they can fly strongly when they fledge.  To
avoid these potential problems be certain your floors are at least 5" x 5".  
Narrow, cramped designs like the Peterson and Gilwood Bluebird Boxes are
totally unacceptable in a Tree Swallow project.









How many boxes should you build?
The best number depends on your habitat's quality, the size of your field, and
your energy and budget.  4 to 8 boxes is good for starters.  That's enough so
you can see how individual swallows vary in behavior and nesting, but not so
many record keeping is a chore.  Oh what the heck; if you want to start with
just one, that's ok.  Just start.  If you enjoy your swallows, expand next year.






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Building Boxes
Learn About Birds at Tree Swallow Nest Box Projects
NO!!!
Bluebird box
interiors too small!
YES!