The sex ratio(♂/♀) of plateau pika′s(Ochotona curzoniae) population was studied by re-captured method in the region of the Haibei Alpine Meadow Ecosystem Research Station, Northwest Institute of Plateau Biology, the Chinese Academy of Sciences from April of 2001 to August of 2002. The result showed that there was no significant difference from 1∶1 in adult′s sex ratio in whole breeding season,whereas the sex ratio of juvenile had some fluctuations among different age stages. The sex ratio of the second litter varied significantly from embryo to 60-day-old, but no difference at the first and the third litter. We concluded it was caused by conflict between maternal strategy and juvenile′s strategy. No significant differences of sex ratio were found both in adult and juvenile between 2001 and 2002. The sex ratio of plateau pika before and after overwintering did not vary. In summary, we proposed that sex ratio of plateau pika′s population was not influenced by exogenous factors, but some self-regulation mechanisms may be involved.
