Margaret, I've had many of the decorative type birdhouses as well as the ones specifically made for birds that have doors in the back for easy cleaning but since moving to this house the birds have never used them, whether nailed to a tree or post etc. I think they'd have to be placed quite high for the birds to be interested ... there's a feral cat problem in the community where I live which probably keeps the birds higher in the trees out of the reach of the felines. At our old house the Wrens built nests in the purple martin houses every year.
I left this old bird condo at our old house when we moved. A neighbor told me that a Red-bellied woodpecker drilled larger entry holes last year and was nesting inside ... I was over there recently and forgot to check it out to see if it's still inhabited. Each "apartment" has doors for easy clean out but our tenants are young and I doubt they'd even think of it:
This is one I left at our rental property too; Carolina Wrens used to nest in the top house:
This was at our old house also, it's an Owl house that one of my sisters gave me for my birthday years ago. It wasn't mounted high enough for owls to use but woodpeckers enlarged the opening and moved in one year. It eventually blew out of the tree during a hurricane (empty of any nest at the time thank goodness) so it just became yard decoration at the base of the tree until it rotted away:
