About Rhinopithecus roxellana (A.Milne-Edwards, 1870)
Rhinopithecus roxellana, the golden snub-nosed monkey, exhibits clear sexual dimorphism in adults and subadults. Mature adult males are estimated to be over 7 years old. They have large bodies, with very long golden guard hairs covering their backs and cape regions. Their crest is medium brown with physically upright hairs that can be used to identify individual monkeys, while their back (from crown to nape), arms, and outer thighs are deep brown. When their mouths are open, long canines are visible to researchers. Adult males typically measure between 58 cm and 68 cm in length, and weigh around 16.4 kg. Subadult males, estimated at 5–7 years of age, have a similar overall body size to fully developed adult males, but their build is more slender. The golden guard hairs on their cape are short and sparse; their medium brown crests show microbanding, and are in the process of changing from brown. Adult females are estimated to be over 5 years old, and are about half the size of adult males. Their dorsum (from crown to nape), cape, arms, and outer thighs are brown to deep brown, particularly in older females. Golden guard hairs are present on their back and cape, but these hairs are shorter than those found on males. Their brown crests show microbanding. Large, easily visible breasts and nipples allow easy identification of adult females. After pregnancy, females are commonly seen with infants and newborns hanging beneath their abdomens while climbing or walking. Adult females typically measure between 47 cm and 52 cm in length, and weigh around 9.4 kg. Subadult females are estimated at 3–4 years old, and are about two-thirds the size of adult females, smaller than full mature females. Their body hair is brown, and is gradually turning golden, but they do not yet have distinct golden guard hairs. Their medium brown crests also show microbanding, and their breasts and nipples are not as large as those of adult females. Juveniles range from at least 1 year old to 3 years old, and are less than two-thirds the size of adult females, making them quite small. Their body hair is light brown, and gradually turns reddish gold. Hair on the rest of their body (dorsum from crown to nape, cape, arms, and outer thighs) is brown. They do not have recognizable golden hairs on the dorsum or cape area, nor do they have the distinct medium brown crest seen in subadult and adult monkeys of both sexes. Sexual identification is difficult for juveniles, as their external genital organs are still underdeveloped. Infants are estimated to be between 3 months and 1 year old. Their fur is light brownish gray or light brown, and appears white when in sunlight. While they often play with juveniles or other infants, infants spend most of their time near their mothers or nursing. They cling to the front of their mothers, primarily the lower abdomen, for protection, feeding, and nurturing. An individual infant’s sex cannot be distinguished at this age, just like in newborns. Newborn babies are estimated to be less than 3 months old. Their fur is dark to light gray, and turns light brownish gray after about 2 months. Newborns rarely leave their mothers or other females that carry them, a behavior called alloparenting. Sex is also indistinguishable at this newborn stage. Golden snub-nosed monkeys are only found in temperate mountain forests across four provinces in China: Sichuan, Gansu, Shaanxi, and Hubei. They inhabit elevations between 1,500 and 3,400 m. Within this range, vegetation changes with altitude: low elevations hold deciduous broadleaf forests, elevations above 2,200 m hold mixed coniferous-broadleaf forests, and elevations above 2,600 m hold coniferous forests. The average annual temperature in their habitat is 6.4 °C (43.5 °F), with a minimum of −8.3 °C (17.1 °F) in January and a maximum of 21.7 °C (71.1 °F) in July. Home range size varies seasonally, and changes in home range size and location depend on the availability and distribution of food. The total area covered by seasonal home ranges is surprisingly large for this species; one of the largest recorded home ranges covered 40 square kilometres (15 sq mi). Females reach sexual maturity at around 5 years old, while males reach sexual maturity at around 5–7 years old. Mating can occur throughout the year, but peaks in October. Gestation lasts approximately 6–7 months, and births occur between March and June. While male–male competition for mates and female mate choice are common drivers of sexual selection in primates, female–female competition over males is especially important in polygynous species. The golden snub-nosed monkey (also called the Sichuan snub-nosed monkey) is a seasonal breeding colobine species endemic to China, and lives in a multi-level social system. The basic social and reproductive unit is the harem, also called the one male unit (OMU), which consists of a single resident male, multiple adult females, subadult females, juveniles, and infants. In this polygynous species, sexual competition is skewed: females face multiple competitors and display high levels of sexual competition, while the single resident male does not experience within-group sexual competition. Females can have up to 3 babies.
