Snow leopards in Nepal 423
disturbance on the snow leopard we recorded presence/ab- sence of recent human activities/use of the area (e.g. fire- wood collection, livestock grazing, snares, poaching camps and fires), as a proxy. A transect was considered to be dis- turbed if direct evidence for any of these activities was ob- served at least at one location along the transect. A distance of at least 250mwas maintained between consecutive trans- ects, to avoid spatial autocorrelation. Transects were at 3,000–5,038 m, nearly all above the treeline. Surveys were conducted in 2014, during October–November, when mi- gratory livestock graze at lower elevations, resident livestock are fed in stalls, and human disturbance is minimal.
Bharal survey
While conducting sign surveys along transects we also counted bharal using binoculars and spotting scopes (Schaller, 1977; Shrestha & Wegge, 2008). To determine population structure and recruitment we recorded the age class and sex of each bharal seen. Following Schaller (1977) and Wegge (1979), bharal were categorized as adult males (7+ years old; horns curved and .45 cm in length), subadult males (4–7 years; horns curved backwards, with a length of 30–45 cm), young males (2–3 years; horn length 15–35 cm), adult females (.2 years), yearlings (both sexes, 1–2 years) and young (,1 year). Additional information on group size, particular characteristics and composition of the group (e.g. male groups), location, time and behaviour were recorded for cross checking and to avoid double counting. For the same reason we also surveyed adjacent transects that were within the potential daily movement distance of bharal groups (5–6 km). Surveys were conducted in 2014, during October–November, when bharal herds congregate for courtship and mating and are therefore easiest to count.
Data analysis
Density estimates for bharal within each block were calcu- lated by dividing the number of animals recorded by the ef- fectively sampled area (the area covered by scanning from the survey transects). We expected that mean elevation (mean of elevation at beginning and end of transect), prey availability (number of bharal encountered per transect) and human disturbance (presence/absence of recent human activities/use) would influence the sign encounter rate (Wolf & Ale, 2009; Sharma et al., 2015; Alexander et al., 2016a; Suryawanshi et al., 2017). To test the influence of these potential predictor variables on the number of signs encountered along each transect, we used generalized linear models with a Poisson error distribution and log link func- tion. The predictor variables were standardized to z-scores prior to analysis, which allowed us to interpret the model coefficients and to compare effect sizes between alternative
models.Weassessed collinearity between the predictor vari- ables, using Pearson’s correlation coefficients. We did not include covariates that were substantially correlated (Pearson’s|r|.0.7) in the same model (Dormann et al., 2013). We ranked models using the Akaike information cri- terion adjusted for small samples (AICc; Burnham & Anderson, 2002). Models with ΔAICc,2 were considered to be strongly supported by the data. Weused the R package MuMin to perform model averaging of all candidate models (Barton, 2017), and computed 95% confidence intervals of the beta coefficients for each predictor variable. The model-averaged beta-coefficients of covariates and their 95%confidence intervals were examined to assess the signifi- cance of their effect on leopard sign encounter rate. Confidence intervals that included zero indicated no signifi- cant effect of the covariates. The relative importance of each covariatewas determined bysumming the Akaike weights of the models containing these factors. All analyses were carried out in R 3.4.2 (R Development Core Team, 2017). We calculated the maximum number of snow leopards
that the available bharal population could support following the predator–prey ratio suggested by Oli (1994). We esti- mated the number of bharal that the suitable snow leopard habitat (c. 600 km2; G. Khanal, unpubl. data) could support based on bharal counts in six blocks (a total of c. 200 km2), and then converted the estimated number into biomass. Because there is little reliable empirical information on body weights for each category of bharal, we considered adult male, subadult male, young male, adult female, year- ling and young age classes to have a mean weight of 65, 60, 55, 55, 30 and 25 kg, respectively (Schaller, 1977). We then used the predator–prey weight ratio (1 : 114–159; Oli, 1994) to estimate the number of snow leopards that Api Nampa Conservation Area could potentially support. This ratio was based on findings (Jackson & Ahlborn, 1984) that an adult snow leopard requires 600–900 kg of meat annually (20–30 bharal) after accounting for energy expenditure in a wild snowleopard and the inedible parts of its prey (Jackson & Ahlborn, 1984).
Results
We surveyed 51 transects, covering a total distance of 106 km, with lengths of 900–3,770 m and a mean length of 2,082 m. We recorded 203 snow leopard signs on 35 transects (Table 1), with a mean encounter rate of 1.91 signs/km. We excluded scats from the analysis because we were uncer- tain of identification to species. Scrapes were the most frequently detected sign (n = 89, 0.84/km), followed by pug- marks (n = 67, 0.63/km). The highest encounter rate of all types of sign was in the Tinkar block (2.35/km; Table 1). The predictor variables elevation, human disturbance and prey availability were not highly intercorrelated
Oryx, 2020, 54(3), 421–428 © 2018 Fauna & Flora International doi:10.1017/S0030605318000145
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