In general, the sub-tropical (_valle_) and temperate (_cabezera de valle_) regions of Bolivia are healthy and agreeable, have a plentiful rainfall, moderate temperature in the shade, and varied and abundant products. There is a high rate of mortality among the natives, due to unsanitary habits and diet, and not to the climate. In the tropical _yungas_ the ground is covered with decaying vegetation, and malaria and fevers are common. There are localities in the open country and on exposed elevations where healthy conditions prevail, but the greater part of this region is considered unhealthy. The prevailing winds are easterly, bringing moisture across Brazil from the Atlantic, but eastern Bolivia is also exposed to hot, oppressive winds from the north, and to violent cold winds (_surazos_) from the Argentine plains, which have been known to cause a fall of temperature of 36 deg. within a few hours. According to the _Sinopsis Estadistica y Geografica de la Republica de Bolivia_ (La Paz, 1903), the average mean temperature and the annual rainfall in eastern Bolivia are as follows: 10 deg. S. lat., 90.8 deg. F. and 31.5 in. rainfall; 15 deg. S. lat., 86 deg. F. and 30.7 in. rainfall; 20 deg. S. lat., 81 deg. F. and 30 in. rainfall; and 25 deg. S. lat., 76.8 deg. F. and 29.3 in. rainfall. _Fauna._--The indigenous fauna of Bolivia corresponds closely to that of the neighbouring districts of Argentina, Brazil and Peru. Numerous species of monkeys inhabit the forests of the tropical region, together with the puma, jaguar, wildcat, coati, tapir or _anta_, sloth, ant-bear, paca (_Coelogenys paca_) and capybara. A rare species of bear, the _Ursus ornatus_ (spectacled bear) is found among the wooded Andean foothills. The chinchilla (_C. laniger_), also found in northern Argentina and Chile, inhabits the colder plateau regions and is prized for its fur. The plateau species of the viscacha (_Lagidium cuvieri_) and the widely distributed South American otter (_Lutra paranensis_) are also hunted for their skins. The peccary, which prefers a partially open country, ranges from the Chaco to the densely wooded districts of the north. There are two or three species of deer, the most common being the large marsh deer of the Chaco; but the deer are not numerous. The armadillo, opossum, ferret and skunk are widely distributed. The amphibia are well represented throughout the lower tropical districts. Alligators are found in the tributaries of the Paraguay and their lagoons, lizards and turtles are numerous, and the batrachians are represented by several species. Snakes are also numerous, including rattlesnakes and the great boa-constrictors of the Amazon region.