Occupancy and Detection:
This study provides the first ever occupancy estimate for sloth bears
from Nepal. Sloth bears were elusive species with less than a half (p=
0.44) probability of detection. Their signs were detected in 21 out of
the sampled 45 grids, giving a naïve occupancy of 0.46. By explicitly
incorporating the imperfect detection of animals into the occupancy
estimate, the proportion of area occupied by sloth bear in Chitwan
national park substantially increased (Ѱ = 0.53). An increase in habitat
occupancy by 15% over the naïve estimate highlights the importance of
considering the imperfect detection when studying sloth bears.
Our estimates are comparable to earlier studies on sloth bears outside
Nepal (See Table 4). Habitat occupancy estimates for the sloth
bear have varied between 0.54 to 0.83 in India. This difference might be
because of difference in the home range of the species. The home range
for sloth bears in Nepal is estimated at 9-14 sq.km in Chitwan (Joshi et
al .1995) which is lower than in India estimated at 12 sq. km for a
female and 85 sq. km for a male (Yoganand et al. 2005) and higher than
that estimated for sub-species Melursus ursinus ornatus at 2.2
and 3.8 sq.km in Srilanka (Ratnayeke et al. 2007, 2021) respectively for
female and male sloth bears. Additionally, most of the reported studies
of sloth bear occupancy in India are from the Western ghats that has one
of the largest blocks of contiguous forest cover and diversity of
habitat conditions consisting of semi-evergreen, tropical moist, dry
deciduous, thorny forest and scrub interspersed with agricultural area
and rocky outcrops while our study area is relatively homogenous with
small grasslands patches interspersed in a deciduous forest habitat. The
occupancy-abundance relationship of species tends to be linked (Gaston
et al. 2002; Zukerberg et al. 2008) particularly at the small and
homogenous areas (Hui et al. 2009). Considering our occupancy estimate
of 0.53 obtained from our sampling of the study area, the suitable
habitat inside the park is ~500 sq.km and the population
around ~100-150 individuals. It indicates that sloth
bears have fairly wide distribution throughout the park, with relatively
higher occupancy (psi >0.53) areas along the northern
boundary of the park (Figure 5) . Both Laurie & Seidensticker
(1977) and Garshelis et al (1999) recognize that there is uneven
distribution of sloth bears with high density in the alluvial
floodplains along the bank of Rapti river in north part of the park and
relatively lower density on rest of the park dominated by upland Sal
forest.