Looks like I was able to lure the pair back to my box that went and nested elsewhere for their 1st brood. I did it using mealworms that I lightly coated with calcium carbonate. They are now feeding their fledglings. I truly believe the house sparrows harassing them played a role in them nesting in another place. I trapped and disposed of three male sparrows and for the past few weeks my nest box has been vacant and sparrow-free! Now the bluebirds are using my box for their 2nd brood! I’m super excited to have them come back!!