One's for rosellas or lorikeets; one for large parrots; and one for pardalotes. The parrot boxes both have "exotic bird excluders", the thin pieces of wood partially covering the entrances. Parrots like to chew open entrances to their nests, while exotics can't, and won't fit in. The pardalote entrance is too tiny for other species.
These are the birds most likely to move in, just in case you're unfamiliar with them. I've seen all of them in our garden over the last year.
Yellow-tailed Black Cockatoo,