THE EFFECT OF MAN 549 



near the Himalayas. Elephant, buffalo, and rhinoceros were formerly 

 common. Lions ranged widely into the steppe region of India; they 

 are now restricted to a small area in the extreme northwest. This is the 

 last phase in the reduction of the range of the lion in western Asia, 

 where successive stages are documented in historic records since the 

 time of Herodotus. Tigers were hunted near Delhi until the middle of 

 the nineteenth century; they are now practically absent from that 

 region. Following the decrease in large carnivores there came the usual 

 increase in deer and rodents such as is now occurring in the Canadian 

 forests. With further destruction of woodland and more intensive 

 agriculture, the wild ungulates also decreased, and there followed the 

 increase in insects, birds, and small mammals such as squirrels and 

 rats, like that which is happening now in parts of the United States. 



In unusually dry seasons both human and non-human populations 

 are brought to or beyond the verge of starvation. During such years 

 the remaining antelope herds invade the farm lands from their normal 

 refuges in the more barren hills. All sorts of plants are eaten; there 

 is severe over-grazing, which brings back earlier stages of the vegeta- 

 tional succession, and a reinvasion of large predators results. 



Aquatic life. — In order to lessen the danger from floods, and to 

 make the rich bottom lands available for cultivation, the courses of 

 rivers are straightened, their banks protected by levees, or even faced 

 with masonry. Quiet bends and stretches of dead water, which are rich 

 in plant life, disappear, and with them go the feeding and spawning 

 grounds of many fishes and the resting sites of aquatic birds. Dams, 

 built for power, bar the way to the migrations of fishes and furnish 

 breeding grounds for mosquitoes. The refuse of factories pollutes the 

 water and makes it unsuited or even poisonous to many animals. On 

 large rivers the steamboat traffic causes a continuous disturbance of 

 the water, and this traffic necessitates the dredging of channels. 

 Dredging destroys the mud and sand habitat of countless mollusks, 

 worms, and insect larvae, and thereby robs the fishes of their source 

 of food. 



When forests are removed, forest margin conditions frequently re- 

 main along roadsides or fence rows and in farm woodlots, which har- 

 bor a number of forest margin animals. When swamps are drained the 

 effect upon the contained animal life is more striking and the propor- 

 tion of the original fauna that is eliminated is greater than in de- 

 forestation as usually practiced. In California the birds displaced by 

 draining such swamps include the herons, rails, gallinules, song spar- 

 rows, yellow-throated warblers, and tule wrens, and if there was open 

 water, coots, terns, and several species of ducks. 15 Fish, frogs, sala- 



