Winter Habitat Use of Sichuan Sika Deer Cervus nippon sichuanicus in the Tiebu Sika Deer Nature Reserve

Sichuan sika deer Cervus nippon sichuanicus is a subspecies of sika deer Cervus nippon, which belongs to the Cervinae, Cervidae, Artiodactyla (Corbet and Hill, 1991). Sichuan sika deer is distributed in a narrow range along the eastern edge of the Qinghai-Tibet Plateau. This deer is threatened by habitat loss and human disturbance (poaching, grazing, road building) (Zhao et al., 2014a). The wild population is about 1000 individuals (Qi et al., 2014). Accordingly, it is classified as a category i protected wild animal species in China, and listed as critically Endangered in the Red List of China’s Vertebrates (Jiang et al., 2016).

Habitat is crucial for wildlife survival, and understanding the habitat use of target species is useful for designing an animal protection plan (Khadka and James, 2016). Spatial temporal variation affects wildlife habitat use (Dupke et al., 2017). It has been shown that the key factors for habitat use by wild animals varied over different seasons (Chen et al., 2012; Rahman et al., 2017; Dargan et al., 2019), as the environmental pressure altered seasonally. Guo (2002) pointed that due to food availability, winter was the critical season affecting survival of Sichuan sika deer. However, till now, little research was focused on the winter habitat use by Sichuan sika deer, which severely restricts the development of Sichuan sika deer conservation.

To understand the relationship between the winter environmental pressure and Sichuan sika deer habitat use and to assist managers to design more effective protection plans, we conducted the research on the winter habitat use of Sichuan sika deer in Tiebu Sika Deer Nature Reserve. Our goals were to determine which factors had a greater influence on the habitat use of Sichuan sika deer in winter, to detect the habitat characteristics which Sichuan sika deer preferred in winter, and to improve protection plans for Sichuan sika deer conservation.

The study area is in the Tiebu Sika Deer Nature Reserve (abbreviation, TNR), China, which is located on the eastern edge of the Qinghai-Tibet Plateau. Elevation ranges from 2,450 m to 3,800 m above sea level. The annual precipitation is about 650 mm, with only ten percent of rainfall appearing from November to March. The mean annual temperature is 6.7oC and extreme low temperature recorded is -18.9oC. The TNR covers about 260 km2 (Yang et al., 2012), which is a mosaic of forest, bush, and meadow. Forest is distributed mainly in shady slopes, bush distributed mainly on sunny slopes, and meadow occurs mainly on gentle areas (Zhao et al., 2014b).

We established transects along altitudinal gradients in the TNR, ensuring the representative vegetation types could be sampled with a transect (Morrison et al., 1992). Sampling plots were centered on signs of sika deer, were treated as used plots, with a distance not less than 100 m between them along transects. Control plots were established along transects at every 100 m change in elevation.

After each sampling point location was established, the vegetation type was determined. Then, seventeen biological and physical variables (Table I) were measured following the method of Wei et al. (2000), which was used in former sika deer research (Zhao et al., 2014b). We sampled 132 used plots and 62 control plots from January to February 2019 and 2020 (Fig. 1).

For categorical variables, exact goodness-of-fit tests were used to detect the difference between used and control plots, then post-hoc tests were conducted. Since we could not confirm that every variable in our research was normally distributed, both independent sample T tests and Mann–Whitney U tests were used to find the difference between used and control plots.

To identify the key factors affecting sika deer habitat use, information-theoretic approach (Burnham and Anderson, 2002) was used. This investigation has conducted a correlation analysis to test independence between variables firstly. For those variables with a correlation coefficient (Pearson) above 0.5, only one variable remained in the subsequent analysis in order to reduce multicollinearity (Zhang et al., 2011; Torres et al., 2012). Then, GLM models with binomial distribution and logit-link were built. We calculated the Akaike information criterion (corrected for sample size, AICc) to evaluate model fit, using the differences in AICc values (ΔAICc) to assess a candidate set of models of all of the possible combinations of variables. For models with ΔAICc<2, we used model averaging to obtain estimates of each regression coefficient and confidence limits to identify the key factors (Creel et al., 2014).

For categorical variables, both vegetation type and slope aspect showed significant differences between habitat use plots and control plots (Table II). The outcome of post-hoc tests indicated that sika deer preferred bush and south slope, avoiding broad-leaved forest (Table II). For continuous variables, elevation, distance to forest edge, shrub height, shrub cover, shrub density, and herb cover showed significant differences between habitat use plots and control plots (Table III).

The top ten models contained 7 variables, herb cover, shrub cover, elevation, shrub height, concealed condition, distance to forest edge, distance to water respectively, of which, herb cover and elevation appeared in all the ten models (Table IV). The models averaged coefficients showed that, Sichuan sika deer preferred habitat with higher herb cover and lower elevation (Table V).

Table II. Categorical variables in used plots and control plots of Cervus nippon sichuanicus in Tiebu Nature Reserve during winter.

Table III. Continuous variables in used plots and control plots of Cervus nippon sichuanicus in Tiebu Nature Reserve during winter.

Table V. Parameter estimates, standard errors, and 95% confidence limits (CL) of the model-averaged for estimating the habitat use of Cervus nippon sichuanicus.

Note: regard vegetation type (coniferous forest) as a fixed reference factor.

Diet and safety are the basic needs of wild animals (Rozhnov et al., 2015; Fattebert et al., 2019). Food availability varies over time, and winter is the diet shortage season for Sichuan sika deer (Guo, 2002). Previous research indicated that meadow was the main foraging patch of Sichuan sika deer habitat (Zhao et al., 2014b). Our research showed that herb cover was the key factor affecting the habitat use of Sichuan sika deer in winter (Table V), which indicated the importance of the diet need in winter. The safety needs caused Sichuan sika deer to utilize habitat with better concealing condition (Table III). The preference of shrub vegetation (Table II) was due to the fact that shrub could not only provide food but also acted as a shelter patch (Zhao et al., 2014b).

It has been demonstrated that human disturbance is an important factor affecting wildlife habitat use (Filla et al., 2017; Fattebert et al., 2019), while the influence of roads and habitations of Sichuan sika deer habitat use were not found in our results (Tables III and V). This may have been caused by the food availability stress, which forced the deer to utilize the habitat close to roads and habitations, and the protection of Sichuan sika deer by local Tibetans leads to the harmonious coexistence between man and deer.

Compared with summer, winter habitat use of Sichuan sika deer appeared different. In winter, Sichuan sika deer preferred habitat at lower elevation and south slope aspect, which lacked in summer (Zhao et al., 2020). These two factors may be highly related to temperature. Previous study demonstrated that temperature could affect habitat use behaviour in many kinds of large herbivores, such as alpine ibex Capra ibex (Aublet et al., 2009), black-tailed deer Odocoileus hemionus columbianus (Bowyer and Kie, 2009), mouflon Ovis gmelini musimon (Bourgoin et al., 2011), and moose Alces alces (van Beest et al., 2012). The lower elevation and south slope aspect may mainly be caused by warmer habitat selection of Sichuan sika deer. In addition, distance to water is an important factor affecting Sichuan sika deer habitat use in the summer (Zhao et al., 2020), which had little to contribute on habitat use of Sichuan sika deer in winter (Tables III, V). The snow scattered on the mountains served as a water source.

Our results clearly showed that the meadow was important as a food patch for Sichuan sika deer in winter, while water was not a restricting factor. Our results also indirectly demonstrated the influence of temperature on habitat use of Sichuan sika deer. Even though road and habitations had little influence on the habitat use of Sichuan sika deer in this research, considering the huge group of free-ranging livestock and intensive firewood cutting, we suggest the higher protection of the shrub and meadow vegetation especially in winter.

This study was supported by Key Fund Project of Sichuan Provincial Education Department (18ZA0543), Special Fund of Yibin University (2017RC04).

The authors have declared no conflict of interest.