Social Structure
Section snippets
Social Structure
Unlike domestic horses, which are often housed alone, feral horses live with companions in social groups called bands or herds. In all investigations of unmanaged populations with natural age and sex ratios, the most common social unit is the single male harem band, which consists of one adult male, one to several adult females, and their offspring, which are usually no more than 3 years of age. This harem system of organization has been considered an adaptation to seasonally changing ecologic
Structure of Managed Populations
Managed populations of feral horses provide experimental situations that may serve to elucidate the intricacies of social organization.28 On the southern end of Assateague Island, the animals are rounded up annually, and most of the male foals are removed and sold at auction. As a result, the sex ratios of adults is 1 male to 4.5 females. Although the harem system persists, band size may reach 26 animals with up to 15 mares, clearly the result of reduced competition among stallions.20 In the
Demography
Feral horse populations consist of males and females in approximately a 1:1 sex ratio.11., 40. Based on data collected from 8764 wild horses captured by the Bureau of Land Management, foals comprised 14.2 per cent of the population; yearlings, 11.6 per cent; 2-year olds, 12 per cent; 3-year olds, 10.4 per cent; and older animals, 51.8 per cent.29
Feral horses show a distinct seasonality of births. Most foals (96 per cent) in the New Forest were born from April to June, whereas only 4 per cent of
Dominance Relationships
Whenever two horses live together, they will establish a dominant-subordinate relationship. Intragroup dominance hierarchies have been reported for each type of social group. Shortly after they first make contact, one animal displays enough aggression so that the other individual withdraws, thereby becoming subordinate. Thereafter, the higher-ranking horse need only threaten the lower-ranking animal to gain access to a limited resource or to prevent invasion of personal space. Because these
Communication
Horses live in stable social groups in flat, open habitats that enhance communication among them. Not surprisingly, then, they show an elaborate communicatory repertoire, making use of acoustical, olfactory, tactile, and visual signals to communicate details of identity, mood, social status, reproductive state, and present, intended, or likely activity as well as information about the environment. Such communication is important in group cohesion.
Horses create a variety of noises, but this mode
Home Range
Harem bands and bachelor bands occupy specific undefended, nonexclusive geographic portions of the environment known as the home range. This is the area used during day-to-day activities and incorporates not only grazing sites and waterholes but also shade, wind breaks, and refuges from insect pests. The reported home ranges of feral horses range from 0.9 to 48 km2 (Table 2).
Available forage and seasonal changes influence the number of animals that occupy a particular home range and the
Interactions between Harem Bands
Encounters between bands are a consequence of bands having overlapping home ranges and sharing the same resources. During such interactions, harem stallions attempt to maintain the integrity of their band and prevent the loss of mares to other stallions. They protect their mares by driving or herding them with a series of characteristic posturings: pressing the ears tightly to the head, fully extending the neck, and dropping the head close to the ground, often swinging it from side to side to
Marking
Adult males direct a great deal of attention toward the excretions of group members as well as those of members of other groups. Typically, stallions that detect a defecation or urination will smell the excretion, defecate or urinate on top of it, and smell it again before moving away. Adult females and young are much less responsive to excretions but have been observed to respond in a manner similar to adult males.43 Only 4.3 per cent of 186 defecations and 11.2 per cent of 107 urinations by
Mating
Harem stallions have almost exclusive breeding rights to the mares in their harem groups.11., 32., 41. Males from other bands or bachelor groups do manage at times to obtain access to and mate nongroup females, but harem males performed 85.7 per cent of the matings in the Red Desert and 87.5 per cent of the matings in the Pryor Mountains.12., 32.
Most of the matings in multiple male harem bands are performed by the dominant male.41., 47. However, out of 81 matings in multiple male groups in the
Comparison with Other Equids
Among the six equine species, two vastly different kinds of social organization exist. Like feral horses, the Asiatic wild horse (Equus przewalskii)35 and the plains (E. burchelli) and mountain (E. zebra) zebras25 live in small, permanent harem groups composed of females, their offspring, and a harem stallion. Adult males not belonging to harem bands either live alone or live in bachelor groups. Harem groups inhabit large, overlapping home ranges.
On the other hand, Grevy’s zebra (E. grevyi) and
Domestic Horse Management Problems Resulting from Natural Social Behavior
Many of the behavioral problems that occur in domestic horses result because their behavior has changed little since they were domesticated. Solitary confinement in a stall may lead to circling, weaving, pawing, kicking the stall, and self-directed aggression.15 This latter behavior, which is common in stallions, can be reduced by allowing the stallion to interact with mares in a pasture where he can engage in the mating, herding, and marking actions of feral horse stallions.16 Other abnormal
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