So far we have primarily seen how physiological and anatomical adaptations
enable animals—especially reptiles and insects—to survive extreme desert
conditions. Behavioral strategies, however, are also vital in the battle against
heat and drought, particularly for mammals, which are anatomically less well
adapted to the desert environment.
Many species escape the heat of the day by adopting nocturnal habits, hiding
in burrows and tunnels in the sandy soil or in caves and crevices among desert
rocks—all places that have more equable microclimates. Out in the full glare of
the sun, the air temperature may be 45°C (113°F) or higher and the ground
temperature an almost boiling 90°C (194°F), whereas in a cool burrow just 10
centimeters (4 in.) below the desert surface, the temperature may be reduced to
30°C (86°F). This burrowing strategy is adopted only by smaller animals. Any
animal larger than, say, a rabbit, would have to dig its burrow deeper, where the
soil is usually harder and more compact, or where loose earth tends to collapse.
Such a burrow would, in any case, be likely to admit predators.
A huge variety of small desert mammals use burrows, including rat- and
mouselike rodents such
as kangaroo rats, gerbils, jirds, pocket mice, and pack rats. Some of the desertdwelling
ground squirrels, for example, excavate complex burrows up to 20
meters (66 ft.) long, connected by cross-links into a network with eight to ten
entrances and several chambers down to 2 meters (78 in.) below the ground.
Similarly the crassus jird of the Sahara excavates a system with a combined
tunnel length of some 40 meters (130 ft.), more than 15 entrances, and several
chambers serving as nests, nurseries, and food storerooms up to 1.5 meters (5
ft.) below the surface.
Burrow dwellings have other advantages besides their relative coolness.
Tunnels function as relatively safe foraging areas, allowing desert animals to
find food with a diminished danger of themselves becoming food. Ground
squirrels, for example, feed on roots, corms, bulbs, tubers, and other
underground plant parts, while desert moles feast on worms, beetles, termites,
and other small creatures that fall through the walls of their subterranean
galleries. A second advantage of the burrow is the increased humidity found
only a few centimeters beneath the dry desert surface, causing a reduced loss of
body moisture.
Desert reptiles, such as skinks and similar lizards, and invertebrates, such as
scorpions, also make extensive use of caves, cracks, and burrows to hide from
the drying sun and wind as well as from predators. They tend, however, to
occupy readymade natural hollows or old and abandoned rodent tunnels rather
than excavate their own.
METABOLIC WATER
One physiological survival strategy is the exploitation of metabolic
water. Most animals lose more water than they take in. The extra
water is made by the biochemical pathways during digestion.
in the desert metabolic water can be a valuable addition to external
supplies. Metabolic water is a natural product of the chemical
breakdown of food in the body, Animals gain energy from the sugars
they derive from digested food, especially glucose or blood sugar
(C6H12O6) , which are broken down using the oxygen (0) absorbed
from inhaled air. The products of this process are not only energy, but
also carbon dioxide (CO2), Which is exhaled, and water (H2O).
metabolic water Is also produced when breaking down long-term
stores of food, especially fats. This is why so many desert creatures,
from gila monsters to camels, use fat stores, which they use as reserves of both energy and water.