The purpose of installing a nesting box is to provide a SAFE habitat for a cavity-dwelling bird of prey to raise its young and increase that bird’s population. In my case, the nesting boxes are for barn owls, American kestrels and, in a few cases, western screech owls. If a nesting box is installed in a tree or on a wood post, any “climbing predator” can raid the box and destroy whatever is in the box.

The photo accompanying this answer is the least graphic I wish to share. Trust me, it can be a lot worse! You can view YouTube videos where cameras are mounted inside the boxes but some are not for the faint of heart. At least, for wood posts, you can install a baffler such as diamond lath that will prevent predators from reaching the nesting box. To me this is common sense but unfortunately I see other companies and sites promoting the installation in trees.