Mention the words ‘survival expert’ and the first name that comes to mind for most people is Bear Grylls or Sir Ranulph Fiennes. Whilst both men have demonstrated remarkable survival skills in extreme conditions, I would dare to suggest that the ultimate survivalists are found in nature.
The dictionary defines survival as “the state or fact of continuing to live or exist, typically in spite of difficult circumstances or adverse conditions”. As environments have changed over the millennia, animals and plants have had to adapt to challenging circumstances; and nowhere more so than in the arid savanna. The Kalahari, a popular destination for many 4×4 enthusiasts, is home to some of the best survival experts on the planet.
The name ‘Kalahari’ (derived from the Tswana word Kgala, meaning “the great thirst”, or Kgalagadi, meaning “a waterless place”) refers to the absence of surface water from much of the vast 930 000-square-kilometre area that is the Kalahari Desert. Although the word desert is used, it is actually a fossil desert, and the great sand-covered plateau a testament to desert conditions that once more closely resembled the Sahara. The dunes of the Kalahari stabilised 10 000 to 20 000 years ago, for reasons climatologists do not fully understand. Curiously, while many of the modern deserts were created at the end of the last ice-age some 10 000 years ago, it apparently only moderated conditions in the Kalahari, converting a raw sand desert into the grassy, arid savanna we see today.
In this article, I want to focus on just one animal – the Gemsbok (Oryx gazella) – which I believe is the Kalahari survivalist extraordinaire. Through a set of physiological and behavioural adaptations, this majestic antelope is able to tolerate not only the extreme temperatures but also the virtual absence of surface water in its arid habitat.
Perhaps the most remarkable of its physiological adaptations is the ability to allow its body temperature to rise to an incredible 45°C without damaging its brain. (The brain is normally adversely affected by temperatures above 43°C.) This is achieved through a structure known as the rete mirabile (Latin for ‘wonderful net’). Put simply, it is a maze of blood vessels that works like the radiator of your vehicle. Warm blood travelling from the heart to the brain passes through this network. Veins that surround the network carry blood already cooled through evaporation in the nasal passages. Heat is exchanged in this process, lowering the temperature of the blood to the brain. It is a very efficient way of protecting the body and simultaneously avoiding too much sweating, which is a common cooling mechanism employed by most animals, but not one suited to such dry conditions. Gemsbok then radiate any excess body heat at the end of the day as the air cools, and are often seen standing on top of dunes or other elevated areas to catch the evening breeze.
If the rete mirabile is the most ingenious of its acclimatisation strategies, perhaps the most practical adaptation to living in an area with limited water is to drink very little, and Gemsbok are masters of this. Through behavioural and food-selection choices, they are able to go for days, sometimes weeks, without drinking. Gemsbok typically feed in the early morning and evening, and occasionally on moonlit nights, when the moisture content in the plants is higher – the water-content of desert plants increases up to 40% of their total mass at night – and there is also some surface condensation. This, combined with the roots and tubers they dig up and the Tsamma melons (Citrullus lanatus) and wild cucumbers that they eat, provides all the water needed to sustain them − approximately 3 litres per 100kg per day. All the water they ingest is used to maximum effect, and they avoid any activity that might lead to dehydration. Moreover, to further reduce water loss, Gemsbok produce ultra-concentrated urine and dry droppings.
These are only two of many other survival strategies they have evolved, but ones that I think we humans can most relate to. On a Kalahari safari we want that vehicle air-conditioner and cooler-box full of cold drinks – both more complex and energy-inefficient solutions to heat than the gemsbok’s. Oh, and they have no need of a tyre gauge to ensure the correct PSI for sand driving; they have broad-based hooves to give them traction in loose sand!
By Lorraine Doyle