I had Carolina Wrens that had tried to build nests in the nest boxes in some of the coops. Last year I had an infestation on mites in one coop and suspected the wrens had introduced them. Every time a wren would start to build a nest in one of the nest boxes I would take the nest out. I did clean out the nest boxes. I would toss the nest material out of the coops. Apparently they got the memo because they stopped trying to build nests in the nest boxes and moved into the barn.