At my work place, the NIH Animal Center west of Poolesville, MD, we have a 'bluebird trail'
consisting of houses on fence posts.  For a number of years, they have been successful and
occupied by bluebirds.  This year, as I have volunteered to help maintain the houses, I noticed
that there is only 1 pair of bluebirds in the area.  In inspecting the houses, about 6, I found
that 2 were occupied by house sparrows and the rest by tree swallows.  One house, closest to my
building, has the bluebird pair showing interest, but I found a house sparrow inside the house
with a male bluebird.  The house sparrow flushed when I started to open the house, but several
sparrows were lingering the vicinity.  After some online research, I found that house sparrows
will take over bluebird houses, even destroying bluebird eggs and killing nestlings.  My question
is whether, by putting up bluebird houses and not monitoring them carefully, we are merely
breeding more house sparrows to the serious detriment of bluebirds.

John Newman
Kensington, MD