Due to the increasing number of problems Bluebirders have experienced with House Wrens, I'm going to sticky this thread, which is actually a compilation of a couple of different threads on the subject of making a Wren Guard from common things you might be able to find around the house.
To those unfamiliar with it, a Wren Guard is a device used to disguise the opening on a nestbox - to shield it from view of House Wrens that may be in the area. It is by no means foolproof - they tend to work best when used BEFORE a House Wren has found a nestbox. They should be installed only after the Bluebird has laid its first egg, or any time thereafter, and once installed the box should be closely watched to be sure the female has accepted the guard and found her way into the box in time to lay the next egg, or in order to incubate the eggs or brood the hatchlings.
There must be 2 1/2" - 3" clearance between the front of the nestbox opening and the guard itself.
What follows is a discussion of some simple homemade Wren Guards that can be made in an emergency. Please - if you have a House Wren situation, post about it in this forum and we can provide you with additional information. Start a new topic, as this one is currently closed.
OK people I'm going to try this. Let's hope it works. I made this a few years ago in about 2 minutes in an emergency and they have worked so well I won't use anything else.
Well I wish they would have been larger but I DID IT!!! I use a three pound box and I get two of them out of it and they last all season.