Nepal has a large diversity of flora and fauna including a considerable number of mammal species. This diversity is explained by the country’s diverse topography, wide range of altitudinal and bioclimatic zone together with the fact that lies at the point of Indo – Malayan and Palaearctic bio-geographical realms. The Himalayan region is also termed as zone of penetration and limitation by some authors.
The boundary between the Indo-Malayan and Palaearctic regions is the tree line at about 3000m. Of the six Indo Malayan sub- regions as defined by Corbett and Hill (1992) two occurs in Nepal namely; Peninsular Indian Division, and Himalayan Sub-region. The Peninsular Indian Division includes the subtropical plains of Nepal Terai. The endemic sub genera are Nilgai, Four horned Antelope, Black Buck, Indian Palm Squirrel, and Indian Bush Rat. In addition it includes western taxa that penetrated the Indian Peninsula such as Striped Hyena, typical species of drier habitats.
Himalayan sub-region is mainly confined to the midhills areas of Nepal, This is a transitional sub-region with various Palaearctic elements descending into forest below 3000m. Fauna elements above the tree-line have Palaearctic affinities, although some endemic Indo-Malayan elements such as the Red Panda is found up to 4300m.
A total of 181 mammals species have been recorded from Nepal belonging to 39 families of 12 orders. The major mammals represented in Nepal are Rodentia (43 spp), Carnivora (42 spp), Chiroptera (bats with 37 spp.), Artiodactyla (even toed ungulates with 22 spp.), and Insectivores (15 species) and Lagomorpha (hares and pikas with 10 spp).
Primates are represented with three spp, pangolins, shrews, and odd toed ungulates with two species each and elephants, dolphins with one species each. Gangetic dolphins are the only true aquatic species occurring in Nepal.
One rodent species (Apodemus gurkha ) is endemic to Nepal. It occurs in Central Nepal between 2200 m to 3600m. Its habitat is mainly in conifer forest where it is marginally sympatric and syntropic with Wood Mouse (Apodemus sylvaticus).
Pygmy Hog (Sus sylvanius) and Indian Chevrotian (Moschiola memonna) have been extirpated from Southern belt of Terai. Their record of occurring in Nepal awaits corroboration.
The highest diversity of mammals species occur in midhills. However larger and the endangered species occur in the Terai and Siwaliks.
Observation of wildlife is easier in Terai as compared to mountains. Annapurna Sanctuary and Everest region is good for viewing mountain mammals.
Twenty seven mammals have been given legal protection by NPWC Act 1973. The big five (rhino, elephant, Bengal tiger, snow leopard and musk deer) drew attention from conservationist due to the vulnerability from the habitat fragmentation and casualty by poachers.
The Asian one-horned Rhino (Gaida in Nepali) is one of the five species of Rhino found in Asia and Africa. They are endangered and occur in Royal Chitwan National Park. They have been reintroduced to Bardia and few to Shukalphanta. They graze singly or in small group in elephant grass, where they also retire during the heat of the day.
Wild Asiatic Elephant, the stock of the domestic trained elephants are part of the culture in South Asia. Ganesh the elephant god is widely worshipped by Hindu devotees. They occur in small number in the protected area and bordering areas with India. Some of the wild males in musth period sired several babies from domestic stock. They frequently come to conflict with human while feeding on the crop fields, damaging property and injuring human. Resident populations are found in Bardia National Park. Raja Gaj the tallest living male Asia Elephant resides in Bardia.
Hoofed animals include the deer, antelopes, mountain goats, wild sheep, largest wild cattle Indian Bison (Gaur) and Arna (wild Buffalo). Sambar Deer is the biggest deer species found in Nepal. Chital Deer is the most commonly found deer and a staple prey species of Tigers and Leopards. Elusive Hog Deer predominantly inhabit the flooded grassland and retreats to nearby forest during flood. Widely branched antlers of Barasingha (twelve point antler), the Swamp Deer dominate the grasslands of Shukla Phanta. It is the biggest herd of its kind in the world. Barking Deer is found from Terai forest to the Himalayan Forest. Musk Deer, is exclusively found in Himalaya. Musk pod is widely sought by poachers, which as aromatic use. Gaur, the largest wild cattle of the world inhabits the Churia foothills of Chitwan and descends to the flood plains of Rapti River during the dry season for new sprouts and water. Arna, the mighty wild buffalo is found only in Koshi Tappu Wildlife Reserve. About 150+ Arna remains in the flood plains of Sapta Koshi River.
The sure footed animal of the steep terrain includes Goral sometime likened to chamois, Himalayan Thar, Serow both the relative of goat share the habitat of Goral. Serow is more forest species. Blue Sheep inhabits the barren alpine regions, they are in demand for sport hunting. The trans-himalayan species includes Tibetan Antelope, Tibetan Argali and Tibetan wild Ass. Nilgai the tallest antelope of the Sub-continent inhabits in the riparian habitat of Terai Plains. Similarly the endangered corkscrew horned Black Buck is found in lower 100’s in the Khairapur of Bardia District.
The large omnivores of Nepal include the Sloth Bear of the Terai, Himalayan Black Bear of Mahabharat and the Brown Bear of the alpine region. The mighty brown bear may have given the impression of legendary Yeti, the abominable snow man. These bears are bold and face any dangers. Red Panda are the closest kin to the bear family and are found in the forest between 3000 to 4300 meter. They are arboreal in nature and love to feed upon bamboo leaves.
Amazing animals include the Gangetic Dolphins found in the deep channels of Koshi and Karnali River. Curious, gregarious, dolphins tend to congregate while hunting fish and crustaceans, their presence are marked by the puffing sounds produced from the blow hole during surfacing. They are regarded as Bhagirath a Hindu deity but often hunted for fats.
Large cats prowls in the jungle of Nepal. Tiger dominates the Terai and Churia Hills while the Leopard span their range from the plains to the tree-line. Nocturnal in habit they are shy and timid. The Terai Arc Landscape is a priority landscape in Global 200 Ecoregion: “Terai Duar, Savannah and Grassland” of the Eastern Himalayan Ecoregion Complex. This is a promising habitat for the large home range requiring species such as tigers, rhino and elephants along with myriads of other life forms. Tigers are at the apex of the food pyramid and conservation of tigers includes the conservation of vegetation, watershed and the prey population. They are solitary but a dominant male overlaps several female territories. Leopards avoids direct contact with Tiger hence lives in the periphery of the forest. They prey upon the wild and occasionally on domestic livestock. There have increased evidences of their occurrence through out the country especially where the community forest are flourishing. They are among the most adaptable large cats of the world. Clouded Leopard a more arboreal and shy are equipped with longest canines. They live mostly in the broadleaf temperate forest. Snow leopard prowls the vast wilderness of the Himalaya and Trans-himalayan region. Blue sheep is the chief prey species of these endangered and elusive big cats of High Himalaya.