Which of the following is NOT a definite indicator of decay?

A nesting hole is not considered a definite indicator of decay because it can be created by various wildlife, such as birds or mammals, for nesting purposes without necessarily indicating that the tree is decaying. Nesting holes may occur in otherwise healthy trees or in trees that have durable wood, where the surrounding structure is intact and poses no threat to the tree's overall stability or health.

In contrast, a cavity, fruiting structures like fungi, and oozing sap usually signal decay or deterioration within the tree. Cavities indicate that significant wood degradation has started, while fruiting bodies like mushrooms often grow on decayed material, confirming the presence of internal rot. Oozing sap can also indicate that a tree is under stress or suffering from decay, as it may arise from the breakdown of tissue. Therefore, while nesting holes may reflect some activity, they do not definitively point to decay in the same way that the other indicators do.