Species: S. syndactylus
Symphalangus syndactylus, also known as the siamang, is the largest of the many species of gibbons. Both male and female siamangs have black hair and grey or pink throat sacs. They can range in height from approximately 2.5 to 3 feet, and they can weigh from 17 to 28 pounds; although there have been larger siamangs recorded. There is little sexual dimorphism between male and female siamangs, but males are slightly larger than females.
Siamangs can be found in Indonesia and Malaysia, where they live in rainforest and tropical coniferous forest habitats. The primary locomotion style of siamangs (and more generally, the Hylobate family) is brachiation, in which they swing arm-over-arm, from branch to branch, as a source of movement. Siamangs can cover up to ten feet in a single swing, due to the length of their arms. When they are not swinging around, they walk bipedally on the ground, or along branches with outstretched arms for balance. Siamangs have extremely dexterous hands, as well as feet, their big toes are opposable! In the wild, their diet primarily consists of fruit, but they have also been known to eat leaves, small birds, bird eggs, and insects. In captivity, they are fed a broad array of fruits and vegetables, as well as, “biscuits” made especially for leaf eaters, as well as other leafy materials. This diurnal species typically lives 80-100 feet up in the trees of high altitude forests, although they can also live in lowland forests. Siamangs live in tropical climates where the weather lacks seasonality and the annual temperature does not drop below 70 degrees Fahrenheit.
Siamangs are an endangered species. This status is due to several factors which includes habitat degradation, natural disasters, illegal pet trade, and hunting. Siamangs have lost an estimated 70-80% of their habitat in the last 50 years due to the destruction of forest habitats by humans. Habitat loss is attributed to factors, such as: logging, clearing land for agricultural fields, and roads. Forest fires also threaten siamang populations. In the aftermath of a wildfire, offspring survival rates drop as food resources becomes scarce. Despite being a protected species, siamangs are sometimes sold on the blackmarket as illegal pets. Young siamangs are selectively chosen for this illegal pet trading industry. This presents problems for siamangs due to the nature of their social bonds. Parents remain in close contact with their young, and for poachers to take young siamangs away often results in the death of the mother and sometimes her young.
Siamangs have an atypical social pattern compared to other primate groups. Siamangs typically live in small family groups comprised of a pair bonded male and female along with 2 to 3 immature offspring. These offspring are born mostly hairless aside from a tuft on hair on the top of their heads. Siamangs are different from most primates in that there is an aspect of equal parenting between the male and female. The male takes over the responsibility of daily parenting when the offspring is one year old. The family groups of siamangs are very close, they are rarely more than 100 feet from one another. The offspring stay with the family group for 5-7 years until they are mature enough to find a mate, which can sometimes take several years. Unlike orangutans, siamangs do not build nests in trees when they sleep, they sleep sitting upright and huddled together. Siamangs, like other gibbons, are known for their howling and singing. Siamangs have throat sacs that can reach the size of their head that they use to vocalize. These throat sacs allow them to be heard up to two miles away. Their duets act as a method of communication and are a way to reaffirm bonds and howls are usually territorial.
The siamangs we chose to focus on reside at the San Diego Zoo and are named Eloise and Unkie. Unkie was born in 1983 in Miami, FL and Eloise was born in 1981 in the San Jose Zoo. Eloise and Unkie have been pair bonded since they met in 1987. The two often sing duets together, however Unkie typically takes the spotlight and is known as “The Soprano.” Eloise has given birth to seven offspring in her many years with Unkie. They enjoy a diet of mostly fruit, although Unkie often steals food from his orangutan friends with whom he shares a habitat. Unkie and Eloise can be seen along with the orangutans on San Diego Zoo’s live Ape Cam.