Home Ranges of Sloth Bears in Nepal: Implications for Conservation

Sloth bears (Melursus ursinus) are the only myrmecophagous ursid. Ursids generally have large home ranges, often with widely separated seasonal ranges, whereas myrmecophagous mammals tend to have relatively small ranges for their body size. During 1990-93, we captured and radiocollared 18 sloth bears in Royal Chitwan National Park, Nepal, and tracked their movements for ≤3 years to assess whether sloth bears have large ranges like other bears, or if, as a result of their myrmecophagous foraging habits, their home ranges are smaller. Six of 8 males tracked ≥1 year exhibited seasonal home range shifts from grasslands and riverine forests of the alluvial floodplain to upland sal (Shorea robusta)-dominated forest during the onset of the monsoon (median movement date = 1 Jun); however, the 2 smallest males and most females did not make seasonal range shifts to sal forest. After the wet season (May-Nov), males returned to the alluvium (median return date = 14 Nov). Alluvial dry season ranges were smaller (P < 0.05) than wet season ranges, for bears that had moved to the sal and for those that did not, suggesting that alluvium offered a plentiful food supply during the dry season. We propose that digging for termites (sloth bears' primary food) was difficult in alluvium when the ground was saturated, prompting large males to move to better drained uplands. Home ranges of sloth bears in Chitwan were small compared with those of other ursids, and unlike typical ursids, sloth bears were not attracted to croplands outside the park, where they would have been subjected to risks of human-related mortality. Sloth bear populations may subsist in sanctuaries smaller than would be expected for an ursid, given sufficient alluvial habitat.