Native to most regions of the world with the exception of Australia, deer are herbivores that consume grass, bark, twigs, and similar items. In some areas, certain species of the mammals must carry out extended migrations on an annual basis in order to ensure adequate food levels. Typically gregarious, most deer migrate and live in family groups, but males may become solitary and erratic in behavior seasonally. In fact, it is not uncommon for males to enter into vicious battles when competing for mates. Such fights generally involve the aggressive use of hooves and antlers, though tusk-like canine teeth are utilized by muntjacs and other deer species that do not posses antlers.