Highly social, equids communicate primarily by sound. In horses and plains zebras, mothers nicker to warn their foals of danger and whinny when they are separated from each other. Males squeal when about to fight for a female. While males are very competitive and may bite each others' necks and kick each others' faces with their hind legs, female groups typically engage in amicable activities such as grooming each other. However, females do have dominance hierarchies and higher-ranked mares get to graze the choicest vegetation and drink first.
Equids have two basic social systems.
In the first, dominant males live with harems of females that often remain in the same group throughout their adult lives. The area occupied by a particular dominant male and his harem can overlap with areas occupied by other groups. This stable social system is found in domestic horses and takhi, and plains and mountain zebras. In contrast, the system found in Grevy's zebra and the two species of asses has fluid relationships. Adults rarely stay together for more than a few months and most adult males live alone in large territories marked with piles of dung.