Adaptation

Survival in the Desert

With the support of the Ministry of Environment and Tourism of Namibia (MET), the numbers and behaviour of the Wild Horses have been scientifically documented since December 1993. The population fluctuates according to the quantity and quality of available grazing, their numbers ranging between 50 and 280 horses in the 100 years of their existence.

The adaptation of the Namib Wild Horses to their habitat is not genetically evident. Reports about extraordinary resilience may safely be relegated to the realm of myth. Many of the animals captured during the drought of 1992 and taken to farms succumbed to African horse-sickness and other ailments and injuries due to confinement. Adaptation can rather be seen in their behaviour: patterns of feeding and drinking, resting and playing according to the amount of grazing (and hence distances to travel) and prevailing temperatures.

‘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.