Population dynamics of blue sheep Pseudois nayaur in Ningxia Helan Mountain National Nature Reserve, China

Long-term studies of population dynamics are important for conservation biology and wildlife management. We conducted 2790 line transects and observed 12516 blue sheep Pseudois nayaur from 2004 to 2009 in the Ningxia Helan Mountain National Nature Reserve of China, and found that the blue sheep population size fluctuated from 12375 in 2004 to 8188 in 2006 then 13344 in 2009, but did not ascend or decline continuously. Population size was positively correlated with the number of rainy days during the previous year. We divided the reserve into high, middle and low density areas according to average sheep encounter rates, and found that in different density areas blue sheep had different population dynamics, sex ratios and group sizes. Ratios between females and males, females and juveniles, and adults and juveniles were not different across six years in all three density areas. Group sizes increased with population size. We deduce that the blue sheep population will not increase or decrease constantly in the reserve, and that managers should manage varying density areas differently to maximize the conservation of blue sheep.