aggression

In biology, behavior used to intimidate or injure another organism (of the same or of a different species), usually for the purposes of gaining a territory, a mate, or food. Aggression often involves an escalating series of threats aimed at intimidating an opponent without having to engage in potentially dangerous physical contact. Aggressive signals include roaring by wapiti (American elk), snarling by dogs, the fluffing up of feathers by birds, and the raising of fins by some species of fish.

Aggressive signals allow the individual to assess the strength of an opponent and so decide whether to risk a fight. Many species use specialized structures during aggression, such as antlers in deer, or display plumage such as crests in birds. Most interactions end with one individual submitting or withdrawing before physical battle occurs: ‘fights to the death’ are rare in nature.