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The Sloth bear (Melursus ursinus), which is endemic to the Indian subcontinent and Sri Lanka, has declined in numbers in many areas in recent years probably as the result of over-killing and habitat alteration. In the 544 km2 Royal Chitawan National Park in the Nepal terai, we estimated there were a minimum of 55 bears or a crude density of 0˙1/km2. During peak concentrations in the lowlying riverine forest/tall grass habitat in March, the ecological density was 0˙5/km2.

Cubs still with their mothers comprised 24 % of the 161 bears classified between December 1972 and November 1975. Females comprised 48% of the adults classified. Average size of 24 litters was 1˙6 (1–2). Seventy-two per cent of the observations were of lone individuals. Three (an adult female with two cubs), was the largest group of bears seen. The only extended social group observed was the female-young unit although newly independent siblings may remain together for a short time. Maternal relations, adult interactions, tree marking, ranging, feeding and anti-predatory behaviour are described.

Examination of 139 droppings showed that these bears fed on at least 17 different fruits (47% occurrence), flowers, grass, honey, and six different insects (52% occurrence). Fruits were an important food from March to June with individual species predominating throughout their fruiting season. Termites, including Odontotermes obesus, were in the diet for most of the year. The Sloth bear was not observed preying on mammals and according to other observers, only rarely feeds on carrion. The ecological basis for selected aspects of Sloth bear biology and behaviour is discussed.