I attached a piece of PVC to the hole of my BlueBird (HAH) house last year in the hopes of finally ridding myself of these pests and allowing some (any other!) bird to use my box purchased 10 to 12 years ago.  Sadly, although they were not supposed to be able to bypass the "periscope" i installed, they had little trouble with it.  My one consolation these last two years is that i can at least ensure that one pair of H sparrows will NOT be successful in breeding.  After i discard several nesting attempts incl eggs they will usu give up.  Then, someone usu fills the box up with sticks.  I decided that this must be a House Wren, as i noticed one (maybe a pair) hanging in the vicinity of the box singing pretty constantly this year.  Yesterday i removed some Forsytia branches and mulberry "volunteers" to give me a better view of the box from the house.  I want to stress that the branches while impeding my view from the house were several feet away from the
 box at the closest point.  Anyway, what do i see this morning, but a damn H Sp. attempting over and over again to enter the box thru the periscope.  He would actually get his body inside the tube at times before the wren would attack his backside and force him to retreat.  I watched this scene repeat itself 1/2 dozen times before moving on.  I guess my next move will be to install a smaller diameter tube - there's got to be a way to thwart these SOBs...!!!

Jim (Michael) Speicher
jugornought—at—yahoo-dot-com
Bethesda  AT work :(
Broad Run_S. FRED Co  AT home