Deserts




Many of the perennial plants that live in the desert have long tap roots which grow deep down into the sandy soil. The soil is well drained so the water sinks into it quickly but the roots are ready to collect as much as they can. Animals have adapted their bodies and behaviour to survive in the desert. Desert foxes have large ears that let them lose heat. They also hide away in cool underground burrows during the hottest part of the day and hunt for food at night when the temperature is lower.

Do cacti live in every desert?
No. They originally developed in the deserts of North America, Central America and South America. Some have been transplanted and grow in other deserts. Some plants in other deserts have adapted to the hot dry conditions in the same way as cacti and look like them.

What is the largest cactus?
It is the giant saguaro. It grows to about 15 metres high and has side branches which make it look like an enormous candelabra. The surface of the stem is covered in vertical ridges. After rain, the plant tissue between the ridges swells up as the plant stores water in its stem. The saguaro grows in a desert where there are heavy rain showers. It has a huge network of fibrous roots which spread out from the base of its stem. The roots form a huge water-absorbing mat just below the soil surface. When it rains a large saguaro can take up a tonne of water in a day. A very large saguaro may weigh ten tonnes but the water it contains will account for nine tonnes of this weight.

What pollinates the saguaro flowers?
The saguaro produces large flowers which make plenty of nectar. Insects feed on this, but larger animals like the white winged dove and the long nosed bat also visit the flowers and assist in pollination.

How do bats survive in the desert in dry periods?
They migrate to other places, like some birds.

What birds may be found in a desert?
Different birds are found in different deserts. There may be small birds such as larks and wrens; medium sized birds such as plovers and sand grouse; and large birds such as vultures and eagles. One of the most unusual desert birds is the roadrunner. It lives in the deserts of the southwestern United States. The roadrunner is a kind of cuckoo but does not lay its eggs in other birds' nests.
A pair of roadrunners build a nest of twigs and sometimes decorate it with cast-off snake skins. They may rear six chicks. A roadrunner catches its prey by chasing it along the ground. It can reach speeds of almost 40 kilometres an hour. Mice, small lizards and snakes are common, but the road runner may also hide by a rock and rush out at a low-flying swallow.

Are there any more large animals like the camel that live in the desert?
Yes. There are several kinds of zebra, and one called Grevy's zebra lives in some desert regions of Africa. They have larger ears than other species of zebra to help them stay cool in the hot desert conditions. The wild ass is another large desert animal. It lives in the deserts of Asia.

Are there any animals like moles that burrow through the sand?
Yes. In African deserts there are golden moles. They are related to moles and burrow in sand dunes. Their tunnels may collapse as they make them. Mole rats are rats which have become adapted to burrowing. They live in Asia and prefer firm soil. They make chambers in which to store bulbs - their main food. In Australia there is a marsupial which has adapted to burrowing and looks like a mole. It is called a marsupial mole. It has a horny shield on its head which it uses to bore its way through the soil.

How do lizards move on soft sand?
Some lizards have webbed feet which spread out their weight and stop them sinking into the sand. Other lizards make swimming movements like an eel and burrow into the sand. They continue to make these movements to 'swim' through the sand. These lizards have wedge-shaped heads which help them push their way between the sand grains. Legless lizards are highly adapted to swimming in the sand. They have tiny legs. These help the lizard move because they offer little resistance to the sand as the lizard moves through it.

Are their any amphibians in a desert?
An amphibian needs water to complete its life cycle, so few are found in desert conditions. One desert amphibian is the spadefoot toad. When the desert becomes dry the toad buries itself 30cm below the surface of the ground. It makes a chamber, lines it with mucus, and rests. During this time the toad's skin turns leathery so that water cannot escape from it. When the rains return the toads dig themselves out of their burrows and search for mates. They lay spawn in pools and the eggs hatch quickly in the warmth. The tadpoles share the water with microscopic algae and shrimps and other crustaceans and feed on them. As the tadpoles grow, some become cannibals. This makes sure that some are big, fit and ready to change into toads when the pools finally dry up.

How can animals survive without water in the desert?
The animals do get some water. They get it from their food. During the day leaves and seeds may be almost dry but at night when the air becomes cool, water vapour in the air condenses into dew on plants. When the animals feed on the seeds and leaves they also take a drink. Carnivores also get water from the flesh of their prey. Desert animals are also adapted not to lose water. They only produce very small amounts of urine and their droppings are very dry. When they rest in burrows, the air becomes so humid that they lose less water to the air than if they rested above ground.