EFFECT OF NEST BOX MODIFICATION ON REPRODUCTIVE SUCCESS
OF EASTERN BLUEBIRDS AND COMPETING SPECIES


SHERRI K. STOLARZ
Department of Biology and Chemistry
Lake Superior State University
Sault Ste. Marie, Michigan 49783  USA



	Abstract.  The Eastern Bluebird (Sialia sialus), once a
common Michigan songbird, has experienced an alarming decrease in
numbers.  Scientist estimate that there is now only one Eastern
Bluebird in existence for every ten that lived only forty years
ago.  This dramatic decline in population can be directly related to
loss of habitat and competition with other species.  The Eastern
Bluebird is an obligate secondary cavity nester and must rely on
other species to create these cavities.  Today most cavities are
provided by placed nesting boxes.  In an attempt to increase the
reproductive success of Bluebirds , regular nesting boxes were modified
to include a false entrance to discourage competing species.
Fifty-four boxes were monitored from May-August of 1992.  Of these
boxes, sixteen were modified while thirty-eight were regular nesting
boxes.  The reproductive success of Bluebirds using the modified boxes
was 18% higher then those using the regular boxes.  A Chi-sguare test
of independence found that Bluebirds used the modified boxes more
than expected.  While competing species were successful in their use
of regular boxes, they failed to use modified boxes.  Reproductive
success of the Eastern Bluebird increased by 32% in comparison to
two previous years of study.



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Peakall, D.B. 1970.  The Eastern Bluebird; its breeding season,
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