Den site selection by marmots
The underground structure of marmot dens is very complex, and digging a complete burrow requires a lot of work. Animals tend to use the smallest investment of energy to get the greatest return (Mcfarland 1993). Marmots decide where to dig their dens only after careful consideration, and, therefore, environmental factors (i.e., the terrain and plant traits) have an important influence on their site selection behavior.
We found that den density on shady and sunny slopes was higher than that in flat areas (Fig. 2; Fig. 10). Topographic characteristics directly affect the moisture and thickness of the soil. Dens located on slopes may allow a more extensive system of burrows to be excavated (Garrott et al. 1983). A den must be dry and have clean underground shelters in which marmots can live (Shi 2007). Although flat areas are conducive to digging burrows, alpine meadow have frequent precipitation during the warm season and rainwater can easy flow into the den. Therefore, the den density is lower in flat areas. The soil layer on the shady slopes in this region is thick (~1 m) relative to that on the other two regions (He and Li 2016) and is therefore convenient for marmots to build their underground den systems. In areas where the soil is shallow and the lower layer is rocky, it is difficult for marmots to excavate burrows. A study that looked at den site preference indicated that Arctic foxes like to dig dens on slopes with thin permafrost (30 cm) (Garrott et al. 1983). Marmots like to excavate their burrows on sunny slopes, in addition to their need for a dry and comfortable habitat, they also benefit from basking in the sun and staying warm, which is vital for avoiding cold temperatures and to avoid freezing in winter after they hibernate (Shi 2007).