COOL
HEADS UNDER A HOT SUN
Gemsbok and springbok are the quintessential desert antelope. Although they are not confined to the Namib or even Namibia as such, they are adapted to cope with the driest conditions found in southern Africa. They drink water when it is available, but can do without it for months on end, as they obtain enough from the plants they eat.
They instinctively migrate to places where fresh grass sprouts after rain. The rest of the time they prefer to graze in the dark hours, when dead grass contains three times as much moisture as it does in daytime, absorbed from dew or fog or even direct from unsaturated air. They also dig up bulbs, tubers and roots for water. In season they consume wild melons and other fruits for the sappy flesh.
Desert antelope are physiologically adapted to pass a minimal amount of moisture when they urinate and defecate. As a consequence their urine is almost as thick as treacle and their faeces are just about dry. It is vital for them to conserve body moisture.
Their behaviour places further limitations on water loss. As far possible they restrict their movements to night-time and seek shade in the heat of day. When they do find it necessary to go into strong sunlight, they generally face the sun head-on, so as to minimise the body area exposed to solar radiation. Gemsbok are wont to stand on top of dunes to catch cool winds at the close of day.
Like all mammals gemsbok and springbok sweat to keep cool, but in the desert they need to keep this within safe limits. If conditions become extremely hot they inevitably reach a point where they cannot afford to lose any more body moisture to evaporation.
In such circumstances they simply stop sweating, the first stage of a physiological process that regulates brain temperature, even as body temperature climbs to potentially lethal levels. They survive only because the carotid rete, a kind of "radiator" peculiar to desert antelope, cools their blood before it reaches the brain.
When they stop sweating, their body temperature -- normally 35,7ºC -- soars as high as 43ºC. In response they start to pant rapidly such that blood in their nasal veins is cooled through evaporation. As this blood flows through an elaborate network of blood vessels just below the brain, the carotid rete, it encounters and cools hot blood that is being pumped through arteries from the heart to the brain.
The temperature of the arterial blood falls through 3ºC before it enters the brain, enough to make the difference between life and death.
Both gemsbok and springbok form herds, but dominant males are solitary and territorial. Only territorial males mate. The gestation period is nine months for gemsbok and six months for springbok. Females give birth to a single offspring at any time of the year as long as enough grass is available to them for lactation.
GEMSBOK
(Oryx gazella)
The national antelope
Size: shoulder height
1,2 m.
Mass: 240 kg.
Horns: both sexes; longest 1,2 m.
Trademark: in profile they resemble unicorns, except for the coloration.
Habitat: desert and open savannah.
Status: common and secure.
SPRINGBOK
(Antidorcas marsupialis)
The only gazelle in southern Africa
Size: shoulder height
0,75 m.
Mass: 41 kg.
Horns: both sexes; longest 492 mm.
Trademark: when they are startled or alarmed, they bounce away ("pronk")
on all fours, head down and back arched.
Habitat: desert and open savannah.
Status: common and secure.
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Fruit-eating
carnivores Brown hyena (Hyaena brunnea) and black-backed jackal (Canis mesomelas) are carnivores that are driven to eat wild fruits to quench their thirst in the Namib Desert. Their favourites are nara fruit, tsamma melons (Citrullus ecirrhosus) and gemsbok cucumbers (Acanthosicyos naudinianus). A brown hyena was once seen to consume no fewer than 18 tsamma melons in one night with a water content of about 11 litres. It is estimated that almost half the diet of lactating females consists of tsamma melons and gemsbok cucumbers. When normal food is scarce, black-backed jackal are known to subsist mostly on plant foods, especially nara fruit. On parts of the Namib coast brown hyena and black-backed jackal live almost exclusively on seal pups and afterbirth. |
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Namibia Guidebook. |
