I have 3 bluebird houses I bought at the Koszta church auction. I bought 3 guards to put on front to help keep sparrows out . It also keeps woodpeckers from enlarging opening. Dh has to redo the houses so i can clean them out and check to see is "who" is nesting there. Got book that shows the nest. And if it looks like they just threw the nesting material in it's a sparrow. Right???? Anyone have Bluebirds. When do they migrate back????