Herd level

A herd of horses is made up of several reproductive units (family groups) usually roaming together and doing the same kind of activity (grazing, resting, etc.). Distances between family groups vary, particularly depending on the season. For example, Przewalski's horses of different family groups that may gather close together to keep insects away with their tails in summer, will be separated by tens of meters in winter. There is also a hierarchy of family groups within a herd, which is particulalry expressed when they have limited access to resources.

Group level

Hierarchy exists within a given harem or family group, and each member has a specific function:

Dominant stallion: in charge of reproduction (stallion covering a mare shown to the right) and group cohesion; dominates youngsters and usually females; plays a prominant role in protection against predators.
Females: initiate different social actions like drinking, grazing or even scratching; look after their offspring.
Youngsters: sometimes take care of their brothers and sisters.

When in heat (oestrus), young females often get away from their natal family group for a few hours, or even a few days, to mate with males from other families. Normally they permanently leave their natal group at 2 or 3 years old to join another family group, either of their own volition or chased out by their father. On their arrival in a new family group young females are lowest in the dominance hierarchy.

Young males usually leave their family group at 2 or 3 years old, either of their own volition or chased out by the dominant stallion, they then join a bachelor group. Within this group their main activity is playing, as a form of training in fighting skills, which leads to the establishment of a dominance hierarchy. At 4 or 5 years old the bachelors start coming close to the family groups to try to detect females in heat. They will then try to make contact with them if possible.

Individual level

Vocal communication
Horses have a limited vocal repertoire, as they almost always maintain visual contact. However they use some vocal expressions, such as the famous whinny which is used when they lose sight of each other.

Olfactory communication
"Flehmen" (when the nostrils are turned up and the upper lip raised and curled back) allows inhaled air to go through the vomero-nasal organ, rich in olfactive cells. As a result, a great deal of information about the sniffed item or individual is transmitted to the horse. This behaviour is particularly used by adult stallions to detect the smell of mares in heat from their faeces or urine, and is also observed during the first few hours after the birth of a foal.

Flehmen

Visual and tactile communication: Interactions
Interactions are classified into 9 categories according to their context or social function:

"Proximity interactions"
Naso-nasal contact
Grooming
Play (hind leg kick, fore leg strike, chase, etc.)
"Dominance interactions" (charge, head threat, hind leg kick, bite, etc.)
Submission
Cohesion (herding)
Stallion rituals
Fights

Click here for a description and pictures of these interactions

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