Probably best to have a 1 1/2" entrance for our largest Eastern Wren. Yes-easily attracted to a nest box.

Hi Dave! I do have a pair of Carolina Wrens in the yard, and mine do NOT choose a nestbox, even when there are many options available to them here. However, my parents live 15 minutes from me, and they always have them nesting in a little birdhouse which is hung in a tree in their yard.Go figure? Seems like some of them are prone to choose unconventional nesting places, like an old boot left out on the porch! I have heard that the House Wrens further north are crazy for nestboxes, to the extent of causing problems for other cavity nesters. I don't get them here.

I have three nest boxes, all the 1 1/2 inch "bluebird" entrance holes and I also have lots of Carolina Wrens but have never once seen them even enter one of the boxes, much less use it. But, having said that, a friend on another forum posted a photo of a Carolina Wren inside a bluebird box sitting on eggs! So it does happen, just not often I think.

I think Carolina Wrens can easily fit through a 1" hole, but will probably pick a site other than a nice nesting box for their nest. I have a nest of them right now in my garage. They come and go through a crack at the bottom of the garage door. The nest is in a box that has the lid cracked open just a bit. Once the babies are ready to go, I'll leave the garage door open a few inches so they can follow their mother out into the world. Carolina Wrens are creative nest builders. I have had them nest in nail aprons hanging on the wall and buckets. I have had them nest under the house, in the crawl space. They try to nest in my gas grill and lawn mower if allowed to. I have seen them checking out parked cars for possible nesting spots.

They nested in my horse trailer spare tire one year, and if I leave the garage door open at all they're inside checking out the shelves of tool boxes

Carolina Wrens are delightful! We had a pair nest in one of our nestboxes last year, the first year we had nestboxes out.

One of the wrens would periodically peek out the entrance, and one would stand on the picket fence nearby and sing so loudly and expressively, like a little opera singer singing "This is MY house!" It cracked me up.

The entrance hole on the nestbox is 1-1/4" and wrens and chickadees fit through just fine.

Wishing you Carolina Wrens in your yard! :)