Dear enemy effect

The dear enemy effect or dear enemy recognition is an ethological phenomenon in which two neighbouring territorial animals become less aggressive toward one another once territorial borders are well-established. As territory owners become accustomed to their neighbours, they expend less time and energy on defensive behaviors directed toward one another. However, aggression toward unfamiliar neighbours remains the same. Some authors have suggested the dear enemy effect is territory residents displaying lower levels of aggression toward familiar neighbours compared to unfamiliar individuals who are non-territorial "floaters".