The best bet is to move your boxes atleast 100 - 200 feet away from brushy areas.

I moved mine to the neighbor's yard. Haven't had wren problems since. Doesn't mean I'm not dealing problems though...just lost babies myself...it's so frustating!!!

House Wrens are difficult to deal with once they have seen the entrance hole.You can use a Wren guard before they arrive on the scene to conceal the entrance holes.I have never had a Wren kill baby Blues.I have heard that they will throw babies out when they are small.
michelle

House wrens are only a threat to Bluebird eggs and new hatchlings until they are about 6 days old, after that the wren can no longer pick them up and throw them from the nest which is what a wren will do to baby birds. If you had almost fully grown babies killed in the nest it was probably due to House Sparrows, the wren maybe came afterwards and filled the house with sticks. If you have wrens in the area once the Bluebird lays the first egg you can install a wren guard, but you would need to watch closely to make sure the Blues accept it, some don't. A wren guard is made of cardboard and comes down off the front of the nestbox and down to conceal the hole of the box from the frontal view, sides can be added to prevent a wren on the top of the nestbox looking down over and stills seeing the hole. Info on this is on the sialis.org site. Also to prevent House Sparrow attacks you can add a sparrow spooker to the nestbox once the first egg is laid, it is to be taken down right after fledging. This info is also on the sialis site. Good luck!

Donna

House wren just killed 4 - 11 day old baby bluebirds. They were pecked in numerouse places, one was headless, hanging on the inside from the entrance hole. After cleaning and returning the box to the pole, the house wren immediatly started filling it with sticks.