关键词: 贺兰山, 岩羊, 群体组成, 种群结构, 季节性变化

Abstract: From March 2001 to February 2002, we observed 690 groups with 3 929 blue sheep ( Pseudois nayaur), including 129 solitary individuals, in Helanshan Mountains at the northern extent of the species'range. Each month, we surveyed blue sheep in 8 sample lines (3 - 4 km each) within 3 ravines. The blue sheep population had been protected for 20 years, and we noted that animals were easier to be observed than in 1984. Blue sheep primarily used low hills with sparse grassland at elevations of 1 400 -1 800 m. Population density was estimated at 8.3 individuals/km², higher than that of blue sheep on the Qinghai2Tibet Plateau. The
solitary consisted of 60% males and 40% females, which appeared throughout the year except December. The mean year-round herd size was 5.5, but varied with season. This group size was smaller than the blue sheep distribution within the Qinghai-Tibet Plateau and neighboring ranges, we attribute to topographic differences between the Helanshan and the Qinghai-Tibet Plateau. The average size of male herd was 4.5, while female herd was 3.5. With such male herd had a higher average within its range than female herd in Helanshan because female-infant group occured with high frequency. The mean size of mixed-sex groups was 8.0. The year-round mean sex ratio (F:M) was 100∶71; however, during February-June varied from 100:130 to 100:155 (i.e. , favored males), whereas during July-December varied from 100:43 to 100∶68 (favored females). The year-round adult female: young ratio was 100:481 Among males, age groups 3.5 - 8.5 years old constituted 63.9 %, whereas 1.5 - 3.5 year old and over 8.5 year old ramswere observed significantly less often.

Key words: Helanshan Mountains, Blue sheep, Group composition, Population structure, Seasonal change