Will predators attack your swallows?
There's always danger of predation, so protecting your nesting birds is a crucial
responsibility for you as a nest box project manager.  Finding boxes emptied of eggs or
young, or discovering discarded wings, legs and clumps of feathers below a box is
terribly disheartening.  
Please take steps to reduce chances of predation.  
Careful choice of project site and proper location of boxes will limit risk of predators
finding your boxes (click Here for box placement guidelines), but you should also try to
prevent predators from
reaching any boxes they do happen to discover.

What animals predate nesting Tree Swallows?
  • Raccoons, cats, and opossums will kill and eat any adults and young they can
    pull out of boxes.
  • Raccoons are especially dangerous because if they find one box and can
    predate it, they look for other boxes and may predate every box in a project.

  • Squirrels are also important predators of cavity-nesting bird eggs and young,
    and if box entrances are too small squirrels can chew their way in.  And
    chipmunks, though cute, predate more bird nests than most people realize.  
    Photo below by Barry Scully.

  • Weasels are so slender they can enter most boxes they can reach.  The photo
    below of a Short-tailed Weasel exiting a predated box is by Barbara Russell.

  • Most snakes can't climb poles, but a few species can, and will enter boxes to eat
    eggs, young or adults trapped inside.

How can you stop predators from reaching boxes?
  • Make it difficult and unpleasant!  The best method is to attach a predator guard
    to the pole below the box.  
  • You should use a guard on every box because raccoons and climbing snakes
    can get up even thin metal poles surprisingly easily, as the photo below taken
    during experiments conducted by bluebird expert Keith Kridler demonstrates.  

  • Conical and Stovepipe Guards (see below) may be effective with some
    predators, but they can be expensive to make and very expensive to buy.  

  • Hardware Screen Guards or Noel Guards that project out around the
    entrance hole are less expensive, but they make it difficult and time-consuming
    for adult swallows to access nests when feeding nestlings and are dangerous for
    nestlings that may climb out on them and fall.  (Note the overlarge hole and small
    dimensions of the box below, obviously not a good design for Tree Swallows).

  • We think modified Purple Martin Tunnels, like the ones below, are safer
    alternatives to Noel Guards.  Click Here to learn how we adapt them for Tree
    Swallow boxes and gourds.

Our System - Can and Grease Predator Guards:  
We use simple, cheap guards made using large juice or restaurant supply cans.  

  • Can ends are removed and the sides cut in strips that are bent out.
  • Note: One cut goes all the way through so the can will fit around a pole.
  • Warning - Can edges may be sharp!

  • The cans are supported by three pieces of house construction "hanger strap"
    fastened to poles by hose clamps.  

  • Rounding the portions of the hangers that touch the poles makes them fit better
    and allows them to be tightened more securely.

  • Three or more can guards are then stacked loosely on top of the hangers.

  • Adding a band of engine grease about 4 inches wide directly below the predator
    guard makes the barrier even harder for predators to pass (see below).  
  • Plus, this grease also discourages ants from reaching nests.  
  • Some ant species will build nests within bird nesting material inside boxes, where
    they may disturb or injure young birds and cause adult birds to desert.
  • Note: Additional grease may need to be applied during a season.

Caution:  Don't over-do the grease!  Use only a short band, if you use any at all.

Caution:  Don't add can guards and grease until females begin incubating.
  • Most predation by mammals occurs at night.  However, male Tree Swallows
    almost never roost overnight in boxes, and females usually don't until they've
    begun to incubate their eggs.  
  • If can guards or grease are added before or during egg-laying, swallows
    competing for boxes could be injured by the cans' sharp edges or get their
    feathers fouled by grease.

Protecting Boxes from Predators
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