UPSC 1999: "India has the largest population of the Asian X. Today, there are just about 20,000 to 25,000 X in their natural habitat spreading across the evergreen forests, dry thorn forests, swamps and grasslands. Their prime habitats are, however, the moist deciduous forests. The X population in India ranges from Northwest India where they are found in the forest divisions of Dehradun, Bijnor and Nainital districts of UP to the Western Ghats in the states of Karnataka and Kerala and in Tamil Nadu. In Central India, their population is distributed in southern Bihar and Orissa. In the East, they are seen in North Bengal, Assam and a few other states." The animal 'X' referred to in this quotation is