Symphalangus syndactylus

Conservation: CITES – Appendix I; U. S. ESA – Endangered; IUCN – Lower Risk (nt) as S. s. syndactylus and S. s. continentis.

Sumber: Order Primates

Distribution: Barisan Mountains of Sumatra (Indonesia); mountains of Malay Peninsula south of Perak River.

Sumber: Order Primates

Habitat. Lowland, submontane, and montane forests, including dipterocarp forests. Siamangs can inhabit primary and secondary forests, including selectively logged forest, albeit at lower densities. Siamangs are found at higher elevations than sympatric gibbons, potentially facilitated by their larger size that aids in thermoregulation and a more flexible diet that can include higher proportions of leaves. Siamangs are commonly found up to 1500 - 2000 m above sea level and have been recorded up to 2300 m in Kerinci-Seblat National Park.

Sumber: Hylobatidae

Movements, Home range and Social organization. Home ranges of Siamangs are 15 — 24 ha, often with some overlap between groups and sympatric Agile and Lar gibbons. Intergroup encounters at common territorial borders occur regularly. They involve calling by males and females, and males chasing males along the boundary. Daily travel distances are variable between groups, locations, and potentially season. They are 400 — 3000 m / day, generally averaging 1000 - 1200 m. Females usually lead the group when traveling, with independent young following next, then the adult male, and behind them, adolescents. Groups are normally highly cohesive and contain 3 - 4 - 3 - 9 individuals. While usually monogamous, polyandry may occur, with a single female and two, usually unrelated, males. The role of polyandry does not appear to be related to the female’s need for additional help in raising infants because groups with two males collectively provide less parental care than those with a single male. Siamangs are unique among the Hylobatidae because males usually become the primary caregiver for infants during their second year of life. By carrying infants, males reduce female energy output during this phase of reproductive effort, leading to shorter interbirth intervals. At one site, turnover of mates appears to be common, with many instances of pairbond dissolution through individuals of either sex leaving their mate and transferring to other groups. As they mature, adolescents are peripheralized by the adult male and female, and by four years old, they may move behind the group and sleep in trees apart from the rest of the group until eventually they move on to establish a new territory. Dispersing males are evidently quite philopatric, whereas females appear to disperse more widely. Intragroup aggression is most commonly targeted at adolescents. Grooming usually involves the adult male as a member of grooming dyads, most commonly with adult females and subadult males. Duetting in Siamang likely improves pair bonding, although itis also probably a territorial advertisement. Population density is highly variable across studies, probably linked to habitat type, with 2: 4 - 24 - 6 ind / km?. Preference, as seen under higher densities, may be for lowland and montane forests, with hill dipterocarp and submontane forest less preferred. Inverse relationships in densities among Siamangs and sympatric Agile and Lar gibbons in different habitat types have been noted in several studies, suggesting niche differentiation. Densities of Siamangs may decrease in a south-north cline in Sumatra.