How do I know the depth of the hollow?
Depth of the hollow is an important characteristic of hollows, as it needs to be deep enough to provide protection from predators and the environment, but not too deep. Unfortunately, most of the time you probably won’t be able to determine the depth of the hollow, as this is a characteristic that needs to be measured by climbing the tree. However, if it is a pipe hollow, you may be able to guestimate how deep (or long) the pipe hollow is. Likewise, if you are monitoring an artificial cut-in hollow or nest box that is mounted to the outside of the tree, you can again estimate the depth of the hollow.