an Oryx

The three main obstacles to survival in the desert are high temperatures, lack of water and shortage of food. Like birds, mammals have the ability to maintain a constant body temperature regardless of external conditions, and this can be both an advantage and a disadvantage in the desert. This means they can endure a large range of temperatures - but most mammals are unable to tolerate even a small rise in body temperature without encountering problems.

When most mammals get hot they produce sweat through glands in their skin, and the evaporation of this liquid cools them down and helps them maintain a constant body temperature. Some mammals also use panting to produce the same effect. Both these methods work admirably, but they have one important drawback where life in the desert is concerned - they involve substantial water loss. Where water is in short supply, animals must minimise loss, so few desert mammals use sweating and panting as their main method of keeping cool.

Because the scarcity of food in the desert limits the number of large animals that can be supported, most desert mammals are small. The Sahara is home to around 40 species of rodents, including gerbils, girds, mice and jerboas. Jerboas have large hind legs that allow them to run very fast. Other small mammals include insect-eaters such as hedgehogs and shrews, and carnivores such as foxes, cats, weasels and genets.

Being small has its advantages and disadvantages. Rodents can burrow into the sand and hide under rocks to avoid the sun's rays. But their small body size means a greater exposure to the sun, causing body temperature to rise more rapidly and more valuable water to evaporate.

Most small mammals make the most of the positive side to their small size, spending the day in burrows under the sand and emerging at night when the temperature drops to a more comfortable level. This option, however, is not available to larger desert-dwelling mammals such as antelopes, gazelles, asses, goats, sheep and camels. Instead they have each developed their own strategies for survival. Camels, gazelles and antelopes are all capable of surviving substantial increases in body temperature, thereby reducing the need to sweat. Gazelles and antelopes can tolerate body temperatures of up to 46° C - and camels can withstand daily body temperature ranges exceeding 22° C. Under normal conditions body temperatures as high as this would lead to dehydration and brain damage, but desert mammals have developed special mechanisms to avoid these.

Camels and asses can drink up to 25 per cent of their body weight in a very short space of time, and they are able to store large amounts of water in their stomachs so that they can go for days without drinking. Camels have the added advantage of being able to store large reserves of fat in their humps, which they can use when food is scarce.

An apparently curious feature of many large desert mammals is their thick coats. In cold climates animals have thick coats to keep heat in and prevent body temperature from falling below a safe level. But dense hair also insulates animals' bodies against the heat. For example, the outermost layer of hair on a camel may be up to 30° C warmer than its body temperature.

Sheep and goats also have thick coats, but their preferred habitat is the rocks and mountains of the deserts, where water and vegetation is more plentiful. In this environment, their agility helps them to survive.

Most of the large mammals that inhabit the desert are herbivores. They get most of the liquids they need from their food - indeed, gazelles can spend their whole lives without drinking. Large carnivores are uncommon in arid environments due to the shortage of prey species, but lions are found in some areas of African desert.

photo courtesy of WWF-UK

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