It is recommend not to install perches on nestboxes for bluebirds. You’ve seen them–the small cylinder pieces of wood added right underneath a birdhouse’s entry hole. They are not really necessary, and the bad news about them is perches can serve the predators by allowing some extra leverage for them to sit by the entry hole and pull out eggs and baby birds! Even wrens and chickadees and most cavity nesters don’t need perches. Take a look at these two photos I took of this male Eastern Bluebird sitting and investigating this nestbox at — and on — this Noel Guard (made from hardware cloth). Question: is this a perch? The answer is: No….it’s a porch! Do the bluebirds mind these guards? Not only do they like “mind” them — they like them! I’ve had nothing but great results using them. Same answer for the other cavity-nesting birds using bluebird nestboxes. They have no issues with these guards. This “cat and raccoon” guard (originally designed by a gentleman by the name of Jim Noel) are also guards to ward off some avian predators, as well — starlings, hawks, owls, jays, etc. I’ve used the vinyl-coated hardware cloth–like the coated better than the plain galvanized hardware cloth — smoother for the birds’ feet and feathers and easier on human hands during the building process. What you see in this picture is plain galvanized. Once you’ve lost bluebird babies and adults to predators inside your backyard bluebird nestbox or on your bluebird trail, you will realize how this guard adds added safety and success to the occupants raising their young until they fledge from the box and into the world.
See how to make them here: http://www.virginiabluebirds.org/wp-content/uploads/2012/12/BB_Guards_12-11-2012.pdf