Den density
According to the area searched by UAVs, the den density on shady slopes, on sunny slopes, and in flat areas was 0.83, 0.97, and 0.60/ha, respectively. The den density on sunny slopes was significantly higher than that on shady slopes and in flat areas (F2, 128 = 3.47, P < 0.05) (Fig. 2), which means that marmots prefer to dig burrows on sunny slopes.