Editor’s Note: This excerpt is from The Equid Ethogram–A Practical Field Guide to Horse Behavior by Sue McDonnell, PhD. 

All of the equid species remaining today can be divided into two general types of social organization: territorial breeders or harem breeders.  The horses, their primitive living ancestor the Przewalski horses (Equus przewalskii), and the common zebras (Equus zebra and Equus quagga) are harem breeders, while Grevy’s zebra (Equus grevyi) and asses (Equus africanus, Equus hemionus, Equus asinus) are territorial breeders.  The following is a brief summary of equid social organization as background for this ethogram.

Harem Breeders

The harem type equids tend to live in large herds comprising several smaller bands. The breeding and family groups are known as harem bands. Each harem band consists of one mature breeding male known as the harem stallion, a few mature breeding females (mares), and their young offspring. The harem stallion stays with his mares and their young offspring all year. The stallion herds and protects the females and young from co-mingling with other bands. The harem stallion also drives and directs the movement of the family whenever it is near other bands or the band is threatened. The harem stallion performs ritualized marking sequences in which he investigates and covers his mares’ feces and urine with his own. Although the harem stallions often appear to human intruders as completely “in charge” of all their harem’s activities, leadership is usually limited to defense from intruders. The actual leader of a harem group in everyday quiet maintenance activities is usually a mature mare. So, for example, treks to water, movement to a new grazing area, or shifts within the day from grazing to resting are typically led by a mare. The mares and their young appear more or less socially bonded independently of the stallion’s efforts to keep them together.

A relatively rare variation of the single-stallion harem is the two-stallion harem. The second stallion is an unrelated mature male that assists the main breeding stallion. The assistant is not allowed access to the mature family mares, but he may on rare occasion breed a young mare that is still with the natal band. The assistant’s main role appears to be defense and help with keeping a large harem together