Grevy's zebras usually mate in August, September, and October, and bear foals during the rainy seasons. After mating, females give birth to a single foal 13 months later. Foals nurse for half a year and may travel with their mothers for three years. Groups of females with young form herds of up to 200 animals. There are no set leaders in these herds but males seem to dominate females.  Males defend individual territories. The females have an average frequency of 1 young per 2 years. The mother does not return to the herd for several days so her young can imprint on her distinctive scent, call, and stripe pattern.  When the bond between the mom and the baby is strong she returns to the herd.