the river. The flat alluvial land is seen as two distinct terraces; the lower terrace is of recent origin on the bank of the Brahmaputra River and the other, upper, terrace is to the north, separated by a high bank running through the park. The whole park is encircled by inhabited villages thus subjecting it to biotic anthropogenic pressure. It has fox holes built by the villagers on its west. Climate The climate in the park comprises three seasons, namely summer, monsoon and winter. The park is subject to subtropical monsoon climate with rainfall occurring mostly during the period from May to September. The average annual rainfall is . Temperature varies during the months of October to March from in the mornings to in the afternoons, in April from in the morning to in the afternoon; and in May to June from in the morning to in the afternoon. Humidity in the park varies from 66% to 95%. Fauna Mammalian species Orang park contains significant breeding populations of several mammalian species. Apart from the great Indian one-horned rhinoceros (68 at the last count), which is the dominant species of the national park, the other key species sharing the habitat are the royal Bengal tiger (Panthera tigris), Asiatic elephant, pygmy hog, hog deer and wild boar. Some important species of the critically endangered and endangered category are the following. The pygmy hog, a small wild pig, is critically endangered, C2a(ii) ver 3.1 as per IUCN listing, and is limited to about 75 animals in captivity, confined to a very few locations in and around north-western Assam, including the Orang National Park where it has been re-introduced. Other mammals reported are the blind Gangetic dolphin, Indian pangolin, hog deer (Axis porcinus), rhesus macaque, Bengal porcupine, Indian fox, small Indian civet, otter, leopard cat (Prionailurus bengalensis), fishing cat (Prionailurus viverrinus) and jungle cat (Felis chaus). The Bengal tiger (Panthera tigris tigris) population was estimated to comprise 19 individuals in 2000, based on pug marks. Fishes More than 50 species of fish have been recorded in the river and channels flowing through the park. Avian fauna Due to its variety of birdlife, including endangered and rare species, the park is listed as one of BirdLife International's "Important Bird and Biodiversity Areas" (IBAs); they consider it the most important bird wet-grassland site on the Indo-Gangetic plain, and one of three "outstanding" IBAs in Assam. It