The oryx (Oryx gazella, also known as gemsbok) is Namibia’s national animal and the Namib’s most successful large mammal. That success is not accidental. The oryx has evolved a suite of physiological adaptations to the desert’s extreme heat that are, considered carefully, among the most remarkable in the animal kingdom.
The Physiology
The core problem for any large mammal in the Namib is this: the air temperature can reach 40°C, and direct sun on a dark surface can push surface temperatures to 60°C or more. Most mammals must keep their body temperature below approximately 40°C to prevent brain damage. At ambient temperatures above 40°C, this requires either significant cooling (sweating, panting, shelter) or extraordinary adaptation.
The oryx’s solution is the carotid rete mirabile: a network of small blood vessels in the nasal region that acts as a heat exchanger. Blood flowing to the brain is cooled by the nasal blood that has been chilled by evaporation in the nasal mucosa. The result is that the brain temperature remains several degrees cooler than the body core temperature, even as the body heats to levels that would be lethal for most mammals.
An oryx can tolerate a body temperature of 45°C without brain damage. This means it can allow its body to heat up through the day without the evaporative cooling that would cost it water. At night, the body temperature drops back to normal. The oryx survives the Namib’s heat by storing it, not by fighting it.
The Water Question
How does an oryx survive weeks or months without drinking? The answer is multi-part.
Water from food: Oryx eat desert grasses and plants that contain small amounts of moisture. At night, when air humidity rises, dry plant matter absorbs enough atmospheric moisture to significantly increase its water content. Oryx feed primarily at night and in the early morning for this reason.
Water conservation: The oryx’s kidneys concentrate urine exceptionally effectively. The nasal chambers recover water vapour from exhaled air before it leaves the body. The capacity to tolerate elevated body temperatures eliminates the need for evaporative cooling through sweating or panting.
Metabolic water: Some water is produced internally through the metabolism of food.
The combination of these mechanisms allows oryx to go for extended periods, potentially weeks or months, without free water access. In severe drought conditions they have been found to dig in dry riverbeds for moisture-bearing roots.
Behaviour at Sossusvlei
Dawn: Oryx are active before sunrise and in the early morning. They move between grazing areas and exploit the moisture in dew-dampened vegetation during the coolest part of the day.
Midday: Oryx stand facing the sun during the heat of the day. This minimises the body surface area exposed to direct radiation (a large animal facing the sun presents its narrowest profile) and allows the nasal cooling system to function most efficiently in the direct flow of warm air.
Dusk and night: Active again as temperatures drop. Most movement and grazing occurs in the cooler nocturnal hours.
At waterholes: When free water is available (after rain or at artificial waterholes), oryx drink. The body temperature is then allowed to drop below normal overnight, essentially “pre-cooling” the animal for the following day’s heat.
Photography
Oryx are one of the best photographic subjects at Sossusvlei because of their visual impact in the dune landscape. A single oryx on a dune face, or a small group at a dune base with the dune walls rising behind them, is one of the classic Namib images.
Early morning drives between Sesriem camp and Dune 45 reliably encounter oryx in good light. The dune margins around the 2×4 parking area also regularly hold oryx in the early morning.