Horse Behavior Herd Dynamics

Horses are highly social and intelligent herd animals. Like all creatures, equine social behavior developed to help the species survive.

Feral and wild horse herds are usually made up of small bands containing mares, their foals, and immature horses of both sexes. There is usually one herd stallion, though occasionally the stallion may allow a few less-dominant males to remain with the group. Horse "herds" in the wild are better described as groups of several small bands who share a common territory. Bands are usually on the small side, as few as three to five animals, but sometimes over a dozen. The makeup of bands shifts over time as young animals are driven out of the band they were born into and join other bands, or as young stallions challenge older males for dominance. However, in a given closed ecosystem such as the isolated refuges in which most wild horses live today, to maintain genetic diversity the minimum size for a sustainable wild horse or burro population is 150-200 animals.

In spite of human mythology that portrays the dominant stallion as the ruler of his "harem" of females, the actual leader of the herd is the alpha or dominant mare, popularly known as the "lead mare." This mare is usually one of the more mature animals in the herd. She takes the lead when the herd travels, dictates when the herd moves from one place to another, what route they take, and has the right to drink first from watering holes and claim the best grazing.

Survival dictates that the herd members ultimately cooperate and stick together. As with many animals that live in large groups, establishment of a stable hierarchy or "pecking order" is important to smooth group functioning. Contention for dominance can be risky since one well-placed kick to a leg could cripple another horse to such an extent that it would be defenseless, exposed, and possibly unable to get to food or water. Therefore, another job of the dominant mare and other higher-ranked animals is to exercise control and moderate aggressive behavior in the herd.

In times of stress, whether from predators or extreme weather, the center of the herd is the safest because it offers the most protection from the elements and is further away from predators than any other part. Because of this, "punishment" of misbehaving members is sometimes delivered in the form of expulsion from the herd--temporarily or sometimes permanently.

Most young horses are allowed to stay with the herd until sometime in their yearling or 2-year old year, when they reach full sexual maturity. Studies of wild herds have shown that the herd stallion will usually drive out both young colts and fillies. This probably is an instinct that prevents inbreeding, so that the herd stallion does not mate with his own female offspring. The fillies usually join another band in fairly short order, and the young colts driven out from various herds usually join together for safety in small "bachelor" groups until they are each able to establish dominance over an older stallion and join a herd of mares.

As a rule, the edge of the herd is where the lowest animals in the herd's social order are found, but also is the domain of the herd stallion, who must fight off both predators and other males who attempt to establish dominance over the stallion. When the herd travels, the stallion brings up the rear, watching for predators and driving straggling herd members on, keeping the group together. This means the herd stallion endures a somewhat quixotic and vulnerable existence. He lives on the periphery of the herd, exposed to predators and bachelor stallions who will fight him. His value to the herd exists only as long as he can retain his dominance. Because there are always many young, unattached stallions about, he can be easily replaced by a strong and healthy successor at any time.

Biologically, and depending on the physical environment available to a herd in the wild, there is only a need for one stallion for every 10 to 20 mares. Domesticated stallions, with careful human management, often "cover" more mares in a year than is possible in the wild. Traditionally, Thoroughbred stud farms limited stallions to breeding between 40 and 60 mares a year.

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