COMMUNITIES IN DRY, OPEN LANDS 455 



Succulent plants and juicy fruits here and there may satisfy the liquid 

 requirements. In the llanos. Cactus melocactus serves to quench the 

 thirst of mules after they have knocked off the thorns with their 

 hoofs. 25 Large herds of antelopes and zebras of the South African 

 steppes live on melons (Citrullus coffer), which are juicy and green 

 just at the beginning of the drought; later, they scrape juicy tubers 

 out of the ground. 26 Elephants and kudus chew out the juice of the bow 

 string hemp (Sansevieria) in order to secure water. 27 Many mammals, 

 notably the camel and desert-dwelling mice, have the ability to use 

 water of metabolism. Mammals gather at watering places, at perma- 

 nent springs, at pools that have not yet dried up, at the remnants of 

 ponds and lakes, even about brackish water. During the dry spring of 

 1887, Walter 28 encountered Gazella subgutturosa in countless numbers 

 at the source of the Adam River (Adam-ilen) near the Afgan bound- 

 ary. The more limited these watering places, the greater the assemblage 

 of animals. Part of them stay in the immediate vicinity; others range 

 to greater distances. Monkeys never wander farther than 4-6 km. from 

 water; rhinoceroses, water bucks (Cobus) , and reed bucks (Cervicapra) 

 keep close to water; and in the Australian steppe, the small finches, 

 Taeniopygia castanotis, are indicative of the nearness of water. The 

 elephant, however, travels 30 km. or more from water, and the Namaqua 

 partridge may live 175 km. from any body of water. At the water 

 holes, there is an astounding amount of animal traffic. At dusk and 

 during the day, birds are the principal visitors, many in flocks that 

 darken the sun; the mammals come particularly by night, herbivores 

 and carnivores, singly, in troops, in herds. 29 Even well-filled springs 

 with an abundant flow may be entirely emptied during the night. 30 



When the springs are exhausted and the last pools have dried in 

 the steppe, difficult times ensue for mammals ; they must then migrate 

 and seek new habitats which offer more favorable conditions. The 

 domesticated animals are equally dependent on water, and their owners 

 are compelled to wander with their herds in search of it. The migra- 

 tions of steppe mammals are usually regular; such migrations are 

 carried out by zebras, antelope, and ostriches; and the carnivores — ■ 

 lions, leopards and hyenas — follow them. At times, however, in espe- 

 cially rainless seasons, such migrations end in tremendous catastro- 

 phies; as in the winter of 1863 in South Africa, when duiker antelopes 

 (Cephalolophus mergens) , driven by hunger and thirst, came to the 

 vicinity of human habitations, even into the villages, and perished by 

 the thousands. 31 Similarly regular migrations take place among the 

 birds of the tropics; thus, a number of species of African birds are 

 known to come to the eastern Sudan at the rainy season for breeding, 32 



