Orangutan

Physical Features

• There are three species of orangutans. Zoo Atlanta houses the Sumatran and Bornean species.

• Orangutans are large-bodied apes with long hair ranging in color from reddish-orange to brown, which shields them from rain. Males have longer, thicker hair than females.

• They are highly sexually dimorphic, with distinct differences in appearance between mature males and females. Fully mature males have large cheek pads, called flanges, and are nearly twice as large as females. While both sexes have a hanging throat sac, it is much larger in males. Mature males also have larger canines and more pronounced beards and mustaches.

• Both their cheek pads and their air sacs help amplify males’ long calls and direct the sound.

• Males can grow up to almost 6 feet (70 inches) and over 250 pounds, while females only grow up to a little over 4 feet (50 inches) and 100 pounds. On average, males weigh over twice as much as females (about 190 pounds versus about 80 pounds).

• Their arms are approximately one and a half times longer than their legs. Adult males can have arm spans of up to nine feet. Their hands feature long fingers and opposable thumbs. Their feet, which are equipped with long, prehensile toes, are like a second pair of hands. They also have highly flexible, fully rotating hips. All of these features aid their arboreal lifestyle. Orangutans are the largest arboreal animals in the world.

• While Sumatran orangutans are almost exclusively arboreal, Bornean orangutans, especially males, descend and travel on the ground more often.

• There are notable differences between the two species at Zoo Atlanta. These differences are more apparent in mature males than other demographics. Physical appearance varies greatly between individuals. Genetic testing is the only way to definitively identify an individual’s species classification.

  • • Bornean orangutans typically have darker skin and hair, and males have larger cheek pads and air sacs than Sumatran orangutans.

    • Both sexes of Sumatran orangutan generally have more noticeable beards and longer, denser facial hair.

• Like humans, orangutans have 32 teeth. Both males and females have powerful jaws and dexterous lips. 

Diet: Frugivore

• Wild – primarily fruits but also leaves, flowers, bark, nuts, seeds, insects (termites and ants), and the occasional egg

  • • Wild orangutans spend 40-60% of their time foraging each day. More than 500 plant species have been identified in their diet. Eating soil is not uncommon. Small mammals are rarely eaten.

    • They obtain most of their water from the food they eat or by licking wet vegetation.

• Zoo – leafy greens (e.g. lettuce, kale); vegetables (e.g. carrots, squash, broccoli, celery, onions); fruit (e.g. grapes, apples, bananas, oranges, grapefruit); dry biscuits containing vitamins and nutrients; browse (edible plant material such as bamboo, banana leaves, mulberry, elaeagnus); oatmeal, peanuts and flavored ice as enrichment

Reproduction

• Flanged (fully mature) males advertise their location with long calls which are amplified by their cheek pads and pendulous air sacs. These longs calls serve to advertise the mature male’s location so other males will stay away but females will know which direction to travel for mating. This suggests that females often choose their reproductive partners and cooperatively mate with the male of their choice.

• Males may mate with multiple females.

• Gestation lasts about 8½ months.

• Length of labor varies and ranges from 25 minutes to three to four hours. Females will break the umbilicus by chewing through the cord and they typically consume the placenta. Nursing usually occurs within four to six hours of birth.

• Most births are singletons and twins are rare. Infant orangutans weigh 3-5 pounds at birth. They spend the first 6-8 months of life clinging firmly to their mothers and are in near constant contact for the first year.

• Infants stay with the mother until her next infant is born, usually at least six years. Young males gradually wander farther from their mother and spend increasing periods alone. Females often stay with their mother and play with the new infant, likely learning important maternal skills. Orangutans stay with their mothers longer than any other non-human animal.

• In the wild, males do not care for the young, but mothers spend up to seven to 10 years teaching each offspring valuable life skills such as building nests and finding food. As offspring get older, they start nesting next to the mother (instead of sharing a nest) and slowly move their nest farther away while coming back to visit.

• In human care, males typically live with the female and offspring and most will engage in play with young.

• Female orangutans menstruate similarly to humans. The cycle lasts 20-30 days and begins at 5 to 11 years of age (7 to 8 is average). There is no evidence of menopause in wild female orangutans.

• Female orangutans reach sexual maturity at 7 to 10 years of age, but wild female orangutans generally do not reproduce until they reach 12 to 15 years of age. The Orangutan SSP® does not recommend females to breed before they reach the age of 14.

• Sumatran orangutans have the longest interbirth interval (about eight to nine years) of any great ape. Bornean orangutans have a slightly shorter interbirth interval of six to eight years. Wild female orangutans may only have up to four surviving offspring in their lifetime.

• Males are the dispersing sex. While females may establish a territory nearby or adjacent to their mothers, males leave the area where they were born and travel long distances to establish a territory that may be stable (consistent over time) or transient (moving over time).

Sexual Maturity in Males

• Due to differences between wild orangutans and those in human care, combined with a wide range of individual variation in onset and duration of maturity, it is difficult to identify a “normal” growth pattern for male orangutans. Most commonly, males are sexually mature by 14 years of age, but secondary sexual characteristics, such as cheek pads, air sacs, and facial hair, may not be fully developed until 20 years of age.

• Generally, the first visible signs of sexual maturity in males are changes in facial morphology. This typically begins at 7 to 9 years of age but may begin as early as 5 years of age or as late as 17 years of age. The maturation process can take as little as a few months or as long as 10 years.

• Some males experience an arrested development of secondary sexual features. These “unflanged” males retain their subadult appearance but are likely to be fertile, representing a unique reproductive strategy that has not been documented in any other mammal, with the possible exception of male mandrills.

• Unflanged males are able to avoid competition with dominant (larger) males in their area, but the exact cause of their developmental arrest is unknown. It is believed to be hormonal, as their secondary sexual features may develop quickly in the absence of dominant males.

Interpretive Information

• Orangutans are the only non-human great apes occurring outside of Africa.

• Predators in the wild include the clouded leopard, Sumatran tiger, crocodiles, snakes and humans.

• The name “orangutan” comes from the Indonesian words orang, which means person, and hutan, which means forest. Their name translates to person of the forest.

• Orangutans are highly intelligent primates with well-developed cognitive ability and problem-solving skills. They are known for their simple tool use, their physical strength, and their dexterity.

• Daily, the orangutans at Zoo Atlanta receive multiple forms of enrichment which encourage natural behaviors. Enrichment may include:

  • • Sensory enrichment (novel sights, smells, and sounds such as magazines, essential oils, music, etc.)

    • Social enrichment (visual or physical access to orangutans outside of their social group)

    • Food enrichment (browse, items they do not receive on a regular basis, or regular dietary items in a different form than usual)

    • Tactile enrichment (blankets, chalk, interactive items)

    • Environmental enrichment (changes to their habitat or indoor area or access to new/different areas)

    • Cognitive enrichment (puzzle feeders, cognitive research)

Behavior

• Orangutans are diurnal, spending their nights in arboreal nests. They typically move to a new spot every night. When resting between foraging periods, they may use arboreal or ground nests or even just drape over a large branch. Females also give birth in nests.

• They spend most of their time feeding and resting. Only a small portion of time is spent traveling or engaging in other behaviors such as nest building or socializing.

• These intelligent animals use a wide repertoire of gestures and vocalizations to communicate. Up to 18 different vocalizations have been identified, including a “long call” made by males to attract females and maintain territory. Another common vocalization is a “kiss-squeak” which expresses excitement or fear.

• While play has rarely been observed in the wild (usually between infant and mother), it is not uncommon to see orangutans of all ages engage in play behavior in human care.

• Although behavioral differences have been reported between Sumatran and Bornean orangutans, more research is needed to determine if these are species differences or the result of differences in population densities, competition for resources, or other factors.

Social Structure

• Orangutans are the only great ape species that do not live in large social groups. Their solitary lifestyle is likely a result of their frugivorous ecology. Large social groups would deplete food (fruit) resources in an area very quickly, so individuals must spread out in order to forage for sufficient amounts of food. When and where fruit is abundant, related females may gather to forage while their offspring play together.

• They have historically been considered solitary, but more recent data suggests that while adult males are typically solitary, adult females and young are more social. The most common social grouping is a female with two to three offspring of different ages. It is also common to see unflanged males associating together.

• Males spend approximately 90% of their time alone. Their interactions with other orangutans involve either consorting with a female or interacting antagonistically with other males for control of territory or females.

• Behavioral studies suggest that orangutans exhibit aspects of culture, as evidenced by social groups having larger behavioral repertoires than less social populations. Many behavioral traits are specific to certain populations and absent in others. Behaviors are generally learned from one another and passed on to subsequent generations.

Taxonomy

• Bornean and Sumatran orangutans were historically considered subspecies of Pongo pygmaeus. Taxonomic reviews in the early 2000s provided evidence that they are two distinct species and this classification has since been widely adopted.

• Prior to genetic studies in the 1980s and 1990s, orangutans in zoological populations were managed as a single species. For this reason, there are “hybrid” orangutans with genetic representation from both Bornean and Sumatran species. These individuals do not breed to conserve space and preserve genetic lineages.

• A third species was discovered in 1997 and was scientifically described in 2017. Previously considered as a population of Sumatran orangutan, the Tapanuli orangutan is more closely related to Bornean orangutans than to Sumatran orangutans. The Tapanuli orangutan, named for the districts of Sumatra that are home to the only forest where this species lives, is the rarest species of great ape in the world. Only around 800 individuals are estimated to live in the wild.

• The current classification system recognizes three subspecies of Bornean orangutan, but the population is only managed at the species level due to space restrictions and insufficient subspecies population sizes. Sumatran orangutans are considered a distinct species with no subspecies.

Zoo Habitats

• The Orangutans of Ketambe complex includes three outdoor habitats that are separated by dry moats that are 10-12 feet wide and 12-14 feet deep.

• The climbing structures and ropes provide opportunities for orangutans to engage in a natural behavior called brachiation. This term refers to a method of arboreal movement that involves rotating the shoulder while alternating the arms to swing from trees, vines, ropes, or other elevated materials.

• The orangutan habitats are numbered 1-3, with Habitat 1 being closest to the former World of Reptiles building. Habitat 2 is adjacent to the otter building, and Habitat 3 is located directly behind habitat 2. Due to the dry moats, Habitats 2 and 3 appear to be continuous. In total, the three habitats cover about 1½ acres.

Training at Zoo Atlanta

• The Primate Care Team uses positive reinforcement to teach the orangutans behaviors that allow them to participate in their own care. This makes daily and veterinary care easier for both the orangutans and their care team. Trained behaviors may include presenting body parts for inspection, receiving hand injections, shifting to a specified area (such as to a scale for weight measurements), urinating (for health monitoring), or even participating in ultrasounds and blood pressure readings.

• Positive reinforcement means that desired behaviors are encouraged by pairing those behaviors with something favorable, such as preferred food items. When orangutans produce the behavior requested by the trainer (either a Primate Care Team or Veterinary Team member), they receive a treat such as a peanut, grape or small piece of fruit. All training is voluntary.

• Zoo Atlanta was the first zoo to train an orangutan to participate in several procedures while awake. These were previously only conducted under anesthesia:

  • • cardiac ultrasound – Satu

    • blood pressure reading – Chantek

    • echocardiogram (EKG) – Chantek

Research at Zoo Atlanta

• With some of the largest zoological populations of endangered ape species in the country, Zoo Atlanta has collaborated with other zoos and universities to study orangutan behavior, biology and cognition for decades.

• Many of the orangutans participate in cognitive research using specially designed touch screen computers. Tasks have been designed to study their memory, learning processes, problem solving skills, and other cognitive abilities such as number discrimination. This research uses the same positive reinforcement technique used by animal care teams to train husbandry behaviors.

• You may see orangutans participating in research while in Habitat 2. The Orangutan Learning Tree (large, synthetic tree in the center of the habitat) allows scientists at the Laboratory for Comparative Primate Cognition at Emory University to explore how orangutans recognize individuals through a variety of programs. Their performance can then be compared to that of other primate species, allowing us to learn more about our closest animal relatives.

• In addition to providing valuable information to help us learn more about orangutans, these cognitive research opportunities also provide stimulating enrichment for the orangutans.

• Zoo Atlanta also conducts behavioral observations to better understand how orangutans spend their time. You may see animal care or research team members on the berm behind the habitats collecting this data.

Updated July 2020