ATTENTION: If you need to know how to control NEST MITES click here.

At the Project:
Most nestlings have fledged.  A few late nests, or renests, may still be active.  It's time
to check inside boxes whose nestlings you know have left for certain.  

Bring disposable gloves and a trash bag if you plan to remove old nests.   Also, you
might want to collect a few nests for ectoparasite examination.  If so, take along some
large zip-lock bags.  Although this ranks high on the "ick" scale, it's important to realize
that all songbirds have both
ectoparasites (little critters that live on a bird's outer
body surfaces) and
endoparasites (little critters that enter a host bird's body and live
in or on the bird's tissues or organs).  It's a fact of life.  (Below: a bird flea greatly

To familiarize yourself in advance with swallow ectoparasites click
here to view the
Purple Martin Conservation Association's outstanding page.  Purple Martins are large
swallows that host most of the same types of ectoparasites as Tree Swallows.

Resume checking boxes where young have fledged:
  • Be absolutely certain no live young remain in the box before you go near it!!  
    Be positive feeding has stopped.  If it's day 20 or later, with no sign adults are
    feeding nestlings, take a peek.
  • Open the box a crack, making sure there are no living young inside.
  • Determine number of nestlings fledged by subtracting the number of dead in the
    box, if any, from the number counted alive at day 12 (or your closest count day
    before day 12).

What is the nest like inside now?
  • Wear disposable gloves handling old nests.
  • Late-stage nests are apt to be fouled with feces and smelly.
  • Dead nestlings, if any, add to the unsanitary conditions.

Collect nests for ectoparasite examination:
  • Stand upwind to avoid blowing nest debris.
  • Remove the nest.  Most of it should come out in one or two pieces.
  • If the nest has dead nestlings remove the nest from the box but don't use it for
    ectoparasite examination.
  • Put each nest to be examined in a zip-lock bag and seal tightly.

  • Take nests elsewhere for examination.  Not inside your house!
  • Put a weighted sheet of newspaper or cardboard down to give background
    visibility and to make clean-up easier.
  • Wearing gloves remove a nest from its bag, put it on the paper, and pull it apart.
  • Check out the little crawly things.
  • If you don't want them crawly, microwave the bagged nest briefly.  (But they'll be
    harder to see if they aren't moving).

What ectoparasites should you find?
  • Most Tree Swallow nests are loaded with bird fleas, both larvae (the white curly
    things (below left) and adults (below right).  These fleas specialize on cavity-
    nesting birds.  They won't attack you or your pets.

  • There may be pupal cases of blood-sucking blowflies (below).

  • There may also be bird lice and mites.  Lice can be hard to find, but mites
    infestations may become heavy enough to spot easily.  Mites look like little
    specks, but don't look too closely at little specks - they can jump, on you!
  • The tiny red specks on flange of the nestling below are blood-sucking mites.  

How did ectoparasites get into the nests?
  • Adult fleas, mites, and lice ride in on adult swallows, usually the parents.
  • Once in a box some parasites, especially mites, remain long after the swallows
    have left, overwintering without food, waiting for the birds' spring return.
  • Blowfly adults are attracted by nest odor.  They lay eggs in nest material.  Their
    larvae suck body fluids from nestlings.

Don't ectoparasites harm nestlings?
  • There is considerable debate regarding the effects of parasite infestations on
    Tree Swallow nestlings.  In sum, while it's doubtful Tree Swallow ectoparasites
    kill nestlings directly, there are several possible indirect effects.
  • For instance, although research has shown blowflies have slight overall costs to
    nestling health, high blowfly loads may cause anemia, which could slow nestling
    growth, making them indirectly more susceptible to starvation and hypothermia.  
  • Heavy ectoparasite infestations can also depress nestling immune systems,
    harming their ability to resist diseases and environmental stress, leaving them in
    poorer condition and less apt to survive after fledging.
  • In addition ectoparasites have the potential to transmit infectious diseases to
    their hosts.
  • It's also likely that effects of ectoparasites become more severe when
    environmental conditions deteriorate during cold snaps or rainy periods.
  • In extreme cases some ectoparasite infestations can have disastrous effects.  
    The mites in the photo below left, swarming around an entrance hole, were
    believed to have led to parental desertion and subsequent deaths of six
    nestlings inside the box just before they were due to fledge.  (Photo by Sal the
    Butterfly Hunter).

  • Click here for procedures to control parasitic mites in Tree Swallow

Some endoparasites and subcutaneous parasites can damage tissue in ways
that ultimately cause death.
  • The unfortunate nestlings below were host to subcutaneous blowfly larvae that
    penetrated tissues in their heads and destroyed their eyes.  One can be seen
    exiting the face of the nestling to at right.  (Pictures by Dick Stauffer).  

  • For an excellent discussion of life cycles and effects of both ectoparasitic and
    subcutaneous blowflys on nestling birds click here.

Are all the invertebrates in old nests ectoparasites?
  • No, some critters in nests are harmless or actually helpful.
  • Some eat bird feces, nest material, or cast off feather sheaths and skin
  • Dead nestlings attract insect scavengers, including carrion beetles.

Questions for the next Topic:  Independent Juvenile Tree Swallows.
  • Can you tell juvenile Tree Swallows from adults?
  • What are juveniles doing?  What behaviors do they show?

Ectoparasites of Tree Swallows
Learn About Birds at Tree Swallow Nest Box Projects