关键词: 藏狐, 巢穴, 主成分分析, 聚类分析

Abstract: The characteristics of summer den habitats of the Tibetan fox (Vulpes ferrilata) were studied in Shiqu County in western Sichuan province during July 2001. Over 230 km were sampled by line transects (totally 40 km , ranging between 4 200 and 4 500 m of altitude) . For each fox den , 7 ecological factors (water distance , den direction , slope direction , slope degree , position in the slope , vegetation type and small mammal pika or rodents den number) were recorded in 5 ×5 square meters centred on the den. 91 Tibetan fox dens were found. Among them 54 dens were fully described and classified by a principal component analysis (PCA) followed by a cluster analysis (complete linkage hierarchical ascendent classification on euclidian distance) . The first four factors of the PCA represent 85 % of the total variance. Water distance , slope degree and the position in the slope are the three most important variables contributing to the first factor. This factor represents 42.8 % of the total variance. Small mammal den number and vegetation type are also important in the latter 3 factors. In the cluster analysis , dens were grouped into three main groups (A: 26 dens , B : 22 dens , and D: 6 dens) . Group A is more coincident than group B , and both these two groups comprised the group C. Group C is quite different from group D , water distance is the main reason coursing the difference. The water distance in group C is no more than 500 m , but longer than 800 m in group D. Tibetan fox dens are mainly in middle (6815 % of 54 dens) and sunny or half sunny slope (92.6 %) , lower position in the slope (87.04 %) and with moderate water distance to den ( < 500 m) (87.04 %) . The directions of the fox dens range from 35°to 360°(88.9 %) . Most dens were located in grasslands(96.3 %) with moderate slope (68.52 % are between 5°and 25°) . In addition , small mammal dens were always found in the 5 m ×5 m sample squares , at a various number. It is suggested that the relationship between small mammal dens and fox dens distribution should be studied in the future.

Key words: Tibetan fox, Den, Principal components analysis, Cluster analysis