Most adult zebras stay in family groups throughout their lives. Upon reaching sexual maturity, adolescent mares will leave their original family to form a new one, or are received by other groups. The stallions form bachelor groups with other stallions until they assume leadership of their own family, whereupon they attempt to keep other stallions away. Should a stallion take leave of his group for a prolonged period, on his return he will often find that he has been replaced as head of the family by another. Very old or sick stallions must avoid the other stallions for fear of being injured in the dominance battles. When the herd is dispersed by predators, family groups will come together again over a period of several days. Foals seem to have little difficulty finding their mothers, apparently doing so by smell or by recognizing subtle differences in the pattern of stripes. The zebra has narrow stripes over most of its body, with the black stripes predominating over the white ones.