I get downies roosting in my boxes, and they often "excavate" the interior. I'd just leave it. I do put hole guards on the hole tho so they don't enlarge it. Here is a link that might be useful: Downy bio

Thanks for answering. :) I'm already using the plastic bucket baffle to prevent predators and the next-door neighbor has been kind enough to let me mount the conduit pole on one of the eight foot high 4x4 posts in her privacy fence. This makes the house a total of 17 feet high, and I can lower the house to 10 feet for cleaning by loosening the screws on one side of the pipe strap a bit, although I think nest monitoring this way might impractical. Aas for whether Flycatchers can enter a Martin style SRE, I think I've found my answer. http://nature.gardenweb.com/forums/load/bird/msg061803451680.html I'm still not sure about whether 50 feet is far enough from the house though. :/ I guess I'll just try it and see.

Thinking further about it, I don't need to prop open the cold frame, which would make a 4-foot long narrow opening. I have two ventilation holes (2 by 4 inches) in the back wall, blocked by hardware cloth and 16 inches above the ground. All I need to do is remove the hardware cloth, then install hole reducers to reduce the holes to 2 by 2 inches each. Each hole reducer can also support a shelf/perch INSIDE the box, which will allow the birds to check the interior after entering. The inner shelf will also restrict the downward reach of any predator paws. The box is so big, though, that birds can easily stay out of reach of any predator paws. I thought of putting the cold frame up on the railing of the rear deck, where in a corner position, the railing would support three corners of the frame, needing only one temporary leg for the last corner -- but my wife vetoed that idea (too unsightly). (It was designed to be portable, in three stackable sections of about 30 pounds each, with a hardware cloth plus porous plastic bottom.) We have no snakes of any kind in this suburban area. Rats and mice are under control, because since I have been killing them, there are no more signs of them trying to tunnel into my shop/storage area, which has a dirt floor. But just in case, I can add a smooth hard material to the back wall of the cold frame so that rodents cannot climb up to the entrance holes. The other possible predators are wandering cats (common) and racoons (rare). The inner shelf/baffle will stop them. I have st least a dozen small plastic pots that I can lay sideways in the cold frame in case some birds would like to roost in them. A bed of leaves and perching branches are the other options to offer. As for the 'wren' nestbox, the downy has enlarged the opening to 1 1/4 inches. I cleaned out old twigs and put a pile of sawdust in the bottom.

Agreed, we are still trapping and won't stop. They seem to be slowing down now, I'm not sure why. We don't catch nearly as many despite there still being quite a few around. Hope they are not getting smarter! I bought wood to try out this birdhouse last weekend and will let others know how it goes. http://md.fpemad.com/p2/mansion.htm This one is designed with the Eastern Bluebird in mind. I guess the theory behind the 2 hole mansion home is that they bluebirds feel safer and more confident in chasing off the HOSP if they have an escape route and are not trapped by HOSP in the house. Also, it turns out that purposing making the house smaller to repel HOSP isn't good for the bluebirds. They like a larger space. We had some around at about a month ago but they have since left it seems. I think they will keep nesting through June? Here's hoping I can get this built this weekend and put up. I have removed HOSP nests daily from our current house and 3-4 eggs in total. They just keep building!! So to answer my own OP....no the sparrows will NEVER give up. You must find a way to outsmart the little cretins! Will post on the 2 hole mansion.