Article of interest:

Davis, W.H., P.J. Kalisz, and R.J. Wells. 1994. Eastern Bluebirds prefer
boxes containing old nests. J. Field Ornithol. 65(2):250-253.

Authors found that bluebirds preferred boxes containing old nests in 4
out of 5 instances (experiment done in Kentucky). The experimental
design put up 50 pairs of bluebird boxes in an area with a successful
bluebird trail and minimum human disturbance. One box contained an old
nest and the other box had been cleaned out. Boxes containing old
nests were used in 38 instances and clean boxes in only three
instances.

Authors suggest two possible reasons for the preference of boxes
containing old nests. One is that the bluebirds prefer re-working old
nest material to completely building a new nest. The second is that
boxes with old nests enhance parasite control because of the presence of
wasp (Nasonia) larvae that parasitize blowflies.

Final recommendation was that old nests be left in place until boxes
become too shallow to be attractive to bluebirds. [ed. note: The
research does not support this suggestion. Their research only focused
on one year, it does not follow nest boxes over several years to see if
there is a preference for multiple-years worth of nests over one years,
etc. JP]

Jeff Price Internet: PriceJ at MAIL.FWS.GOV
National Biological Survey
Northern Prairie Science Center Phone: 701-252-5363
8711 37th Street Southeast Fax: 701-252-4217
Jamestown, ND 58401