Possible Nest Box Claimant

My bluebird box (on a post) has finally attracted some attention this spring.  I checked a few boxes today and found this collection of moss and lint: giving me the suspicion we have a Tufted Titmouse involved.  I have not seen any birds at or entering the box so can't be certain my diagnosis is right or that the nest hasn't been aborted.  I had really hoped for bluebirds but at this stage of the game they aren't playing and titmice beat House Wrens every day of the week (wrens took this over last year).  I'll be keeping an extra eye on things to see what comes.