The rut establishes which males are dominant, and each successful male has a group of females. The group stays together until the fawns are born, about four or five months. Deer are by nature gregarius (social) and like to live together. This helps their defence against predators. The details vary between species. The actual defence against attack is decided by the dominant male. He decides whether to stand and, if necessary, to fight. Males keep their antlers for half a year. If they run, deer are outstanding runners. If they stand, they can kick. They will not attack humans unless the male senses danger. He gives warning by posture and sound. Stags tend to join up in male groups for mutual defence once their antlers are shed. The females also join up in large herds which can defend themselves fairly well. Deer stay in these single-sex groups for much of the year.