Three years ago, we erected six tawny owl boxes, two on our farm woodland patch and the others on friends' neighbouring farms.
First year 2016 - Blanked!
Second year - a grey squirrel seemed pretty cosy in one of ours but no luck with the others.
Third year......as in, Wednesday earlier this week - Ta-Da! Two lovely tawny owl chicks ringed from one of our boxes and a brood of three ringed from one of our neighbours.

Result!