In many areas there are a lack of suitable hollows for fauna to nest in. Many landholders often make or purchase nest boxes that have been designed for local species. This something you may like to consider if there are too few hollow bearing trees or the trees are too young to have produced hollows in your area.
One of the responsibilities if you have decided to put up a box, is to make sure you check it on a regular basis. This is made easier if you locate it in a spot where you can actually reach it from your ladder and you go past it on a regular basis to keep an eye on it.
You need to be checking that it is still attached to the tree and the attachment mechanism is not cutting into the tree. Also check whether there is any bee activity so you can get onto eradicating them early (if they are the introduced honey bee).
After the spring flurry of activity open the lid of the box and check whether you need to add or remove any nesting material or remove dead young. If there has been no activity in the box for a number of years you may consider changing the location.