Sheep are a prey species, and their only defense is to flee. Sheep display an intensely gregarious social instinct that allows them to bond closely to other sheep and preferentially to related flock members. Flock mentality movements protect individuals from predators. Flocks include multiple females, offspring, and one or more males. Ewes tend to stay in their maternal groups for life, whereas rams may form transient, unstable, and easily disbanded bachelor herds. If most rams in a group die because of fights or diseases, those remaining join another group. Under standard grazing situations, sheep graze together in casual affiliations; social hierarchies are not as apparent as they are for cattle.