Red-Breasted Nuthatches make their nests in tree cavities.
They apply gobs of sticky conifer resin around the entrance of their nest holes. The nuthatch avoids the resin by diving directly through the hole.
During nest-building, the Red-breasted Nuthatch is aggressive and will chase away nest hole competitors.
Their aggressiveness subsides after the nest is finished, although they remain aggressive towards predators and competitors.