Reproductive Parameters of Wild Rhinopithecus bieti

Animal life activities are rhythmic and affected by seasonal periodicity. Based on 9 years of observations, we estimated the reproductive parameters of a wild, but provisioned Yunnan snub-nosed monkey (Rhinopithecus bieti) group at Xiangguqing in Baimaxueshan National Nature Reserve, Yunnan Province, China. We observed 84 infants (43 males and 41 females) from 41 females between 2010 and 2018. We found the birth sex ratio was 1:1, the female age at first birth was 6.13 years and infant mortality was about 15.5%. Nine years of data showed that the maximum birth season lasted 126 days, and the average length per year was 98.57 ± 18.71 days. R. bieti,characterized by strictly seasonal reproduction, started giving birth on February 1, and this ended on June 7, with a peak reached from March 4 to March 11 (10th week). The mean birth date was March 20 (79.21 ± 29.54 days), and the median birth date was March 11 (71st day). The mean interbirth interval (IBI) was approximately 2 years, and the IBIs among females whose infants had survived for 1 year were found to be significantly longer than those found in females who lost their infant within 1 year. Comparing the reproduction parameters among Asian and African colobines, we concluded that Asian and African colobines tend to have an IBI of 2 years or more, females tend to give birth at the age of 5–6 years, Rhinopithecus species had a strict seasonal reproductive pattern concentrated in February to April. Seasonal changes in food resources and climatic factors may be the main reasons for the variation in reproductive parameters in intraspecific and interspecific comparisons of Asian and African colobines.