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
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.
Dominance and leadership
‘Work’ and ‘Leisure’
During dry conditions, when grazing becomes scarce, the horses have to ‘work’ for the quantity of nutrients they need. They cover vast distances, feed wherever possible and rarely play. Visits to the waterhole are put off for as long as possible. In contrast to domestic horses, thirst causes them very little stress. The horses are accustomed to tolerate a certain amount of dehydration, reducing the time needed and the energy expended in travelling to the waterhole.
During the hot summer months (November to March) they come to drink on average at intervals of 30 hours, while during the cool winter months (May to September) intervals can be as much as 72 hours.
After good rains when there is abundant grazing, the Wild Horses adopt a ‘leisure mode’: they feed at night, and as there is no need to cover vast distances to obtain their fill they remain close to the waterhole for longer periods of time. Up to 80 percent of the herd gathers there. They will drink every day, regardless of temperature, and play and rest. Their leisure time offers the best opportunity for observing them and for taking great photos.
Manure as Supplement
The horses’ diet is made up predominantly of grass. They will also consume their dry nutrient-rich manure. This is a natural behaviour called coprophagy, an energy-efficient way of deriving nutrients, exhibited by a variety of animals and all horses if opportunity allows. The Wild Horses’ manure contains almost three times more fat (1.99%) than the area’s dry grass (Stipagrostis obtusa – 0.7%) and almost twice as much protein (6.1 instead of 3.1%).
As horses don’t digest plant cellulose as efficiently as ruminants, the manure provides a high-energy food and a way of absorbing nutrients which have been excreted undigested. The manure, however, is merely a supplement; less than 1kg of manure is eaten for every 7kg of grass. In the dry Namib Desert, parasitic infestations are curtailed by the dry environment.
Foals, on the other hand, need to eat fresh manure to acquire the essential intestinal micro-organisms necessary for digestion.