Reproductive Parameters of Wild Rhinopithecus bieti

Abstract

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 colo-

Determinants of Harem Size in a Polygynous Primate: Reproductive Success and Social Benefits

“…There may be several reasons for this finding. First, female Yunnan snub-nosed monkeys give birth every two years on average [54], thus reducing reproductive competition during years when they take a reproductive time out. Second, Yunnan snubnosed monkey harems are composed mostly of related females [29], and nepotistic cooperation such as allocare and allonursing may promote successful reproduction.…”

“…This result suggests that strengthening female-female bonds through grooming may be one of the key factors affecting harem size. As mentioned above, Yunnan snubnosed monkeys give birth every two years on average [54], and the number of co-resident females in a harem is limited (the current record of co-resident females is less than seven). Overall, the pressure of reproductive competition was not great, thus obviating the need for excessive social investments into the harem holder.…”

“…From March 2010 to December 2020, a total of 26 OMUs and 1 AMU (182 individuals) were recorded in the research group. Each year, the research group consisted of 5-10 OMUs and 1 AMU, ranging from 45 to 72 individuals [54].…”

“…They live in polygynous one-male units (OMUs) or 'harems' that are part of a larger multilevel society [29,53]. They are characterized by strictly seasonal reproduction and a mean interbirth interval of approximately 2 years [54]. Harem holders possess nearly exclusive mating rights over all females in the harem.…”

Dispersal patterns in Yunnan snub-nosed monkeys

“…Yunnan snub-nosed monkeys Rhinopithecus bieti are an endangered species of Asian colobine endemic to China, inhabiting high altitude mountain forests on the Tibetan Plateau within a narrow area between the Yangtze and Mekong Rivers ( Xia et al 2020a , 2020b , 2020c ). Rhinopithecus bieti forms multilevel societies ( Grueter et al 2020 ) composed of many OMUs and at least one all-male unit (AMU; Ren et al 2012 ; Grueter et al 2020 ; Figure 1 ).…”