Stegmann (1938) recognizes a distinct Mediterranean 

 avifauna of desert grassland, chaparral, and wood- 

 land that is best developed in northern Africa but ex- 

 tends north through Spain, Italy, the Balkans, Tur- 

 key, and southwestern Asia. 



ANIMAL ADJUSTMENTS 



The characteristic animals of the desert are 

 the small herbivorous rodents and the reptiles. Large 

 animals, including the carnivores, are relatively 

 scarce, and population levels of the rodents appear 

 determined more by the availability of food and water 

 than by predation. Among birds on the Arizona 

 desert, insectivorous species are most numerous, then 

 seed-eaters, and lastly carnivores (Hensley 1954). 



Most adjustments grassland species make to their 

 environment continue to be expressed in the desert 

 and additional ones become conspicv:ous (Buxton 

 1923, Sumner 1925, Heim de Balsac 1936, Linsdale 

 1938, Fautin 1946, Hensley 1954, Schmidt- Nielsen 

 in Cloudsley-Thompson 1954). The two most critical 

 environmental factors are the high temperatures, 

 especially during mid-day, and the lack of water. 

 Reptiles have some advantage in that their scaly skin 

 is adapted to prevent rapid evaporation. Moist 

 skinned amphibians and snails are absent except in 

 the immediate vicinity of springs or other bodies of 

 water. 



Animals tend to avoid extreme high temperatures 

 rather than to tolerate them for any length of time. 

 They do this in various ways. The small mammals, 

 snakes, and even insects are largely nocturnal. Birds 

 are active chiefly in the cooler hours of early morn- 

 ing and evening and tend to remain quiet and con- 

 cealed during the middle of the day. Lizards are the 

 most conspicuous animals during the day. Nearly all 

 animals spend their time above ground in the shade 

 cast by the scattered shrubs or rocks, and it is here 

 that they have their burrows or nests. Bird nests 

 occur most frequently on the east and northeast side 

 of plants, where they are shaded from the hot after- 

 noon sun. The intervening ground, fully exposed to 

 the sun's rays, heats up much higher than the air 

 temperature and may not cool down completely even 

 at night, so that small mammals and other animals 

 scurry quickly from the protection of one bush to an- 

 other in their travels for food. Ground surface tem- 

 peratures go well above the upper limit of tolerance 

 of snakes, but some lizards can hold their bodies 

 away from contact with the ground on their long thin 

 legs. Even the grasshoppers come to rest in bushes 

 to avoid the hot ground surface as much as possible. 

 Grasshopper species confined to hot sandy areas 

 have, like the lizards, long slender legs that hold their 

 bodies away from the ground. Many mammals, rep- 



tiles, and insects (ants, crickets) burrow deeply into 

 the ground and thereby avoid the surface heat ; for 

 example, the burrows of kangaroo rats penetrate 

 50-65 cm below the surface near Tucson, Arizona 

 (Sumner 1925). On one day when the maximum 

 air temperature in the shade reached 42.5 °C 

 ( 108.5 °F), and the temperature of the ground sur- 

 face was 71.5°C (160.7°F), at a depth of 10 cm in 

 the burrows the temperature was only 40.1 °C 

 (104.2°F), at 30 cm 29.8°C (85.6°F), and at 45 cm 

 27.9°C (82.2°F). The amount of moisture in the air 

 inside these burrows is also more favorable, being 

 3 or 4 times higher than it is outside (Schmidt- 

 Nielsen in Cloudsley-Thompson 1954). The percent- 

 age of mammal species that burrow increases from 6 

 in forest communities to 47 in short-grass plains, 

 to 72 in deserts. This is in contrast to the decrease 

 in percentage of mammals that are active on the 

 ground level; from 68 to 53 to 28 (Bodenheimer 

 1957). 



Many desert animals are adapted to go a long 

 time without drinking water, but those species that 

 depend on drinking water, which probably includes 

 many of the larger mammals, are restricted to the 

 vicinity of springs, lakes, or ponds. Dew is often a 

 source of water in the early morning. Much of the 

 desert vegetation, particularly the cacti, is succulent 

 and is a source of water to animals. The development 

 of an armor on the plants in the form of thorns and 

 prickles serves as a defense against excessive brows- 

 ing by animals. The flowers and fruits of such plants 

 as the saguaro are important sources of water to birds 

 and other animals. The blood and body fluids of 

 prey furnish ample water for carnivores. Metabolic 

 water obtained with the oxidation of fats and carbo- 

 hydrates in the food eaten is apparently sufificient for 

 many species of small size. Even some of the larger 

 game mammals of Africa find green pasture sufficient 

 for satisfying their moisture needs if they can also 

 obtain shade (Vesey-Fitzgerald 1960). Water is 

 conserved in the bodies of birds, insects, and many 

 desert reptiles by kidney wastes excreted as solid 

 uric acid salts rather than as urine. The urine of 

 mammals is more highly concentrated than in non- 

 desert species, and feces are egested in a dry condi- 

 tion, the excess water having been reabsorbed in the 

 large intestine (Schmidt-Nielsen and Schmidt-Niel- 

 sen 1952). 



After rains sufficient to soak the soil or to refill 

 the shallow ponds, a rapid cycle of events occurs. 

 Herbaceous plants become abundant and bloom. 

 Snails come out of aestivation in the mud. Immature 

 insects and crustaceans become abundant in the 

 water. Termites and ants produce winged forms and 

 mate, and other insects appear in large numbers. 

 Frogs come out of their underground burrows and 

 deposit their eggs ; tadpoles hatch quickly, grow rap- 



338 Geographic distribution of communities 



