Mature red deer ("C. elaphus") usually stay in single-sex groups for most of the year. During the mating season, called the rut, mature stags compete for the attentions of the hinds and will then try to defend the hinds they attract. Rival stags challenge opponents by belling and walking in parallel. This allows combatants to assess each other's antlers, body size and fighting prowess. If neither stag backs down, a clash of antlers can occur, and stags sometimes sustain serious injuries. Red deer are among the mammals exhibiting homosexual behavior.