During the recent past, there has been a sudden decline in the number of wild animals. The major causes of wild life depletion can be summarized as following :
(i) Absence of shelter: The forest vegetation, tall grasses, margins of rivers, uneven grounds, etc. are used as cover or shelter by the wild animals. For instance, the tall grass in the Kaziranga sanctuary is used as cover by rhinos. Once this cover is destroyed animals will not survive even if food and water are available in plenty.
(ii) Reduction in the area of movement: The forest area is being increasingly converted into cultivable lands. This reduces the freedom of movement of the wild animals. Animals like deer, bison, tiger, rhino, etc. are wild animals in the zoo rarely reproduce.
(iii) Destruction of wild plants: For getting more timber, charcoal and firewood, man has cut and destroyed many wild plants which form the main food of these animals. Food is one of the major factors of the habitat which controls distribution and number of wild animals. The absence of chief food may lead to ultimate depletion and extinction of some wild animals.
(iv) Building roads and railways: To improve our transport system a network of roads and railways are built. Most of the roads and railways pass through the dense forests. This limits the area of movement for animals.
(v) Pollution: The rivers and streams that run through the forests and plains contain untreated effluents of many factories which make the river water unsafe for drinking and may even cause large scale death of wild life.