re: Wood Duck Boxes

Also might need to put some screen for the ducklings to climb up or use a chisel to rough up the inside right below the hole. my two cents.

Your not too late. I have five and have three hens so far hitting them laying every AM. Some will lay two times som three times a spring.
One thing I don't see in your box is a ladder. Take some hardware 1/4" hardware cloth and tack a three inch strip from the bottom to the hole. Fold in the sides so no sharp edges. This gives the chicks a foot hold as they claw their way out. I also put 4-6 inchs of Cedar shavings in the bottom. As far as snakes make a guard out of the sheet of hardware cloth and make it as large as possible. Wire it on a pole in water. If you have coons around I wire 3 ft carpet tack strips to the pole. A cool won't be able to climb if these are on the pole. If you can find a cone snake guard buy the largest one you can find and the steepest angle. I have six foot rat snakes and they are hard to keep out. Just have to watch the boxes a lot in April and May.
Good Luck. If you
Put up 2 this year you will need four next year and so on.