The North American deserts are rain-shadow deserts. The wet westerly winds that blow towards the continent across the Pacific Ocean first meet the great western mountain barrier and are forced to rise, dropping their rain on the seaward side. Past the peaks the winds are dry and desert conditions prevail on the extensive plains beyond.
The deserts are not completely barren, but contain an intermittent vegetation consisting of cacti and other succulent plants, normally growing as single specimens, each widely separated from one another. The barren soil surface between the plants conceals a vast network of roots spreading out to collect enough water for each plant to survive.
Among the roots lives the rootsucker, Palatops spp., an animal heavily armoured to protect it from desiccation rather than to defend it from attack. Its head is shielded by a broad spade-like plate and its back is covered by a shiny nut-like shell composed of compacted hair. Its tail and feet are also armoured, but with articulated plates that permit total mobility. The rootsucker moves through the sand using its broad feet like paddles and its head shield as a shovel to reach the roots of succulents on which it feeds, gnawing them with the edge of its head shield and lower incisors.
Among the thorns found in the vertical grooves of cactus stems lives the little desert spickle, Fistulostium setosum, its narrow body covered by spines that are partly for defence and partly for camouflage among the cactus thorns. It has no teeth and subsists entirely on the nectar of cactus flowers which it drinks through its long snout. When collecting nectar it often picks up pollen on its head. The pollen is eventually deposited on the stigmas of other flowers, thus effecting the cross-pollination of the cacti. Living almost solely on nectar, the spickle's digestive system is a very primitive affair, since nectar is very easily broken down.
Lizards and other reptiles do not have the sophisticated mechanisms that mammals and birds have for regulating body temperature. Their temperature is entirely dependent on the surroundings. Several desert reptiles have, however, developed rudimentary devices for keeping themselves cool. The fin lizard, Velusarus bipod, for instance, a small bipedal reptile, has a system of erectile fins and dewlaps on its neck and tail which it raises into the wind when its body becomes too hot. The heat is transferred through the fins via the blood stream into the air. When cooling itself, the lizard typically balances on one leg while keeping the other off the hot desert surface to get maximum benefit from the system.
Small mammals of the desert, like the desert spickle and the fin lizard, are preyed on by ground-dwelling birds such as the long-legged quail, Deserta catholica. Its eggs, which are laid in sand scrapes in sheltered spots beneath bushes or overhanging rocks, are sat on continuously to protect them from the extremes of heat and cold that are typical of the desert climate's daily temperature range.
The breeding cycle of this and many other desert birds is dependent on the rainy season, the birds nesting as soon as the first spring rains appear and continuing as long as the wet season lasts. In unusually dry years no breeding takes place.