Age structure and seasonal changes of Niviventer confucianus population in Loufan county of Shanxi province,China

Objective To study the age structure and seasonal changes of Niviventer confucianus population in Loufan ecological zone of Shanxi province,China,in 2011.Methods N.confucianus was caught monthly.The gender of the obtained N.confucianus was identified and then skull specimens were made.The ages of the obtained N.confucianus were examined according to the growth and wear degree of the upper left third molar(M 3).Then the monthly age composition of N.confucianus was determined.Results The yearly proportion of the juvenile and sub adult N.confucianus in the whole population was nearly 50%.The proportion of adult individuals was 43.13%;Old individuals accounted for only 7.81%,the least.N.confucianus showed significant differences in age composition between different months.The proportions of female individuals in adult and old age groups were less than those of juvenile and sub adult groups.Conclusion Variation of age composition of N.confucianus in different seasons is obvious.Juvenile N.confucianus exists in each month between July and November and the breeding season is long.The reproductive behavior of adult females may make the mortality rate of females higher than the males ',resulting in a declining proportion of female individuals in adult and old age groups.