Breeding groups and bachelors
The Wild Horses have a complex social structure. The core of the herd is made up by so-called breeding groups which usually comprise one or two stallions, several mares and their foals and occasionally other stallions from casual bachelor groups. At times a bachelor stallion will follow a specific breeding group for a few months to several years. This bachelor is then referred to as an ‘outsider’ or ‘peripheral stallion’ and is accepted by the group’s stallions but is not permitted to interact with adult mares in the group. The outsider plays an important part in the group stability and cohesion acting as a barrier and protecting the group from other bachelor stallions.
In normal years, the age and gender structure is about 70 adults to 30 young horses of up to 5 years, 55 stallions to 45 mares, and 50 group stallions to 50 bachelors. Changes in group composition occur regularly because of births and deaths as well as wandering fillies. Mares also transfer to other stallions from time to time or groups split up. Several pairs have stayed together for at least 5-9 years. Significant changes in wild horse groups during the past decade were influenced or caused by human interference (i.e. removal of horses) and in drought situations where older horses died.
The horses are not territorial and several different groups are often observed to graze within 100 metres from another with minimal aggressive interaction.
Due to the unpredictable and patchy rainfall, the horses will move to areas where there is green or more abundant grass at any given time.
Dominance and leadership
A dominant individual is usually defined as the one that has preferential access to a resource (food, water, space, mates etc.) through aggressive threats or actions. There are many different opinions and interpretations of dominance amongst horses. Many people have witnessed how severe aggression can be amongst their domestic horses and therefore believe it to be the same in wild populations.
This is not the case. In the Namib population, threats and shows of aggression are rare in groups and mostly involve mothers with new-born foals. Also, no consistent dominance hierarchies seem to exist between mares in groups or individuals in bachelor groups. Although stallions can direct the movement of their group, this does not necessarily mean they are dominant or that they always have first access to resources. In some cases, mares will also not submit to the herding behaviour of a stallion but try to avoid the stallion’s actions or kick at him. (This usually happens when they have a young foal at foot.)
It seems that dominance hierarchies in wild populations are neither prominent nor consistent. A reason for this could be the space (lack of restriction) they have at their disposal which makes them more content. There is in general little aggression among group members and even between stallions from different groups, considering the high number of encounters between groups. Thus, the aggression or dominance of an individual depends upon circumstances. An example where a typically less dominant horse may become more dominant is in situations of dehydration. Generally, bachelor stallions give way or wait for breeding groups to finish drinking at the waterhole before they move in, but when a bachelor stallion is extremely thirsty he walks to the waterhole straight away and will kick, bite or threaten any other horse already there, if need be.
The presence of a specific “lead mare” in groups is also not clearly evident in the Namib population. The order in which the groups move around or the individual initiating a movement is not consistent and often depend on circumstances. Friendships among individuals of same sex or opposite sexes are more prominent and important in the social knit of the population than dominance or aggressiveness.