About Apes

Gorillas, Bonobos, Chimpanzees, Orangutans, Gibbons and Siamangs are found throughout Association of Zoos and Aquarium facilities in North America.

Are apes monkeys?

Many people confuse apes with monkeys, but they are quite different. There are hundreds of species of monkeys and only 19 species of apes. Gibbons and siamangs claim 13 of these and the other 6 are great apes. There is no single unique feature that defines an ape, rather a suite of distinguishing characteristics. Ape bodies are quite different from those of other primates: apes are generally bigger than monkeys, have a broad chest and don’t have tails. Apes’ arms are considerably longer than their legs. Great apes also have relatively large brains and long infancies and maturation periods.

Who are the apes?

Apes are our closest living relatives. Apes are split into two different groups: greater and small, or “lesser”, apes. The great apes include gorillas, chimpanzees, bonobos, and orangutans. The smaller apes are gibbons and siamangs. Gibbons, siamangs and orangutans are found in southeast Asia while gorillas, chimpanzees, and bonobos live in equatorial Africa. All apes are primarily vegetarians, although chimpanzees, bonobos and orangutans do eat some animal protein.

Chimpanzees

Pan troglodytes

There are four subspecies: the central (P. t. troglodytes), the western (P. t. verus), the eastern (P. t. schweinfurthii), and the Nigeria-Cameroon (P. t. ellioti).

Natural History

Chimpanzees are the most widespread of the apes, found in over 20 African countries ranging from Senegal in the west to Uganda and Tanzania in the east. Not surprisingly, chimpanzees occupy the widest ecological range of all the apes, living in a variety of habitats that include tropical lowland forests, mosaic woodlands, and dry savanna woodlands. Their diverse diet includes 300+ food types such as fruit, flowers, leaves, seeds, small mammals and invertebrates.

Although not the only ape species documented to hunt, chimpanzees hunt at a much greater frequency than other ape species. Hunting frequency varies by chimpanzee population, with some groups hunting almost daily at certain times of the year whereas others have never been observed to hunt. Monkeys are the primary prey item.

Chimpanzees are known for their extensive tool use, which varies depending on population and is considered one of the best examples of non-human culture. Tools are used primarily to extract food- for example, using sticks to fish termites or ants and stones to crack nuts. Like the other apes, chimpanzees build nests that are most often located in the trees.

Wild chimpanzee males and females reach reproductive maturity at 12-15 and 10-12 years of age, respectively. Once females reach maturity, they typically give birth in six year intervals and produce three to four offspring in a lifetime.

Social Behavior

Chimpanzees live in multi-male, multi-female communities that comprise from between 20 to over 100 individuals. The whole community is rarely together but usually splits into smaller parties; this flexible social system is referred to as fission-fusion. Females usually disperse at sexual maturity, whereas males remain in their natal group for their entire lifespan. As a result, males show much higher levels of association than observed in gorillas or orangutans. Males work cooperatively to patrol their territory; intercommunity interactions are often very violent and can result in death.     

Chimpanzees are highly communicative, using both auditory and visual cues. Pant hoots are one of the most distinguishable vocalizations and are usually given when individuals are excited or asserting dominance. In addition, barks are vocalized in hunting and snake alarms, and combination barks or drumming are also used to communicate in different situations.

Threats and Conservation

The International Union for the Conservation of Nature (IUCN) [Link] has classified chimpanzees as Endangered. Increased logging throughout chimpanzee habitat creates a multifaceted problem. The logging itself causes habitat destruction and fragmentation which limits forest availability and disrupts the ecosystem. However, logging also leads to increased access to previously undisturbed areas. This tends to lead to increased commercial trade in bushmeat and disease transmission to chimpanzees and other primates. Besides logging, mining and oil extraction are serious threats to chimpanzees.

It is estimated that there were between 172,000 and 301,000 chimpanzees in 2003, but this number is likely much lower today. Although much of the chimpanzee population remains in protected areas, the effectiveness with which these areas are managed and monitored is constantly put into question.

Gibbons and Siamangs

Gibbons

It is generally accepted that there are 16 to 17 gibbon species in the Family Hylobatidae. They are divided into four groups (genera): Hylobates, Hoolock, Symphalangus, and Nomascus. Click here for a list of all the individual gibbon species.

Natural History

Gibbons are a group of small (lesser) apes found in subtropical and tropical rainforests throughout Southeast Asia. Like all species of apes, gibbons do not have tails.

Gibbons are well adapted for life in the treetops. They move through the forest by swinging from branch to branch in a type of locomotion known as brachiation. They have shortened thumbs and long fingers which allow them to hook their hands over branches while swinging through the forest canopy. They also have exceptionally long arms and shortened legs to facilitate this method of movement. When not brachiating, gibbons may walk bipedally (on two legs) and raise their arms above their heads for balance. Gibbons feed mainly on fruit but also eat a variety of leaves, flowers and some insects.

Gibbons reach maturity at approximately 6-8 years of age. They produce offspring about once every two to three years after a gestation period of 7 to 8 months. Females generally give birth to a single offspring. Infants have the ability to cling to their mothers immediately after birth, which allows females complete range of motion while moving through the forest. Males of most gibbon species will participate in caring for the offspring once they are weaned.

Social Behavior

Gibbons live in family groups that usually consist of a mated pair and their juvenile offspring. Group size usually ranges from 2-6 individuals with young gibbons leaving their family groups between 5-8 years of age. Common social behaviors include playing, grooming and singing.

Gibbons produce amazing songs that can be heard up to 2 miles away. These songs are the most complex of all land mammals and are thought to be used to establish territory boundaries as well as for attracting a mate. Mated pairs also sing together in beautiful duets that can advertise and even strengthen their bond. Gibbon pairs can be identified by their particular song. 

Threats and Conservation

Nearly all gibbon species are classified as endangered by The International Union for the Conservation of Nature (IUCN). Some species have been reduced to a few hundred individuals. The major threats to gibbons include habitat loss and destruction due to logging, clearing of land for agriculture, palm oil plantations and other forms of human development. Hunting for food and for the pet trade is also having a negative impact on wild gibbon populations.

Gibbon Species

Western hoolock gibbon (Hoolock hoolock), Eastern hoolock gibbon (Hoolock leuconedys), Bornean agile gibbon (Hylobates albobarbis), Mountain agile gibbon (Hylobates agilis agilis), Lowland agile gibbon (Hylobates agilis unko), Kloss’s or Mentawai gibbon (Hylobates klossii), White-handed gibbon (Hylobates lar; four subspecies: H. l. carpenter, H. l. entelloides, H. l. lar, H. l. vestitus, H. l. yunnanensis), Javan silvery gibbon (Hylobates moloch; two subspecies: H. m. moloch, H. m. pongoalsoni), Grey gibbon (Hylobates muelleri; three subspecies: H. m. abbotti, H. m. funereus, H. m. muelleri), Pileated or capped gibbon (Hylobates pileatus), Black crested gibbon (Nomascus concolor; four subspecies: N. c. concolor, N. c. furvogaster, N. c. jingdongensis, N. c. lu), Northern white-cheeked crested gibbon (Nomascus leucogenys), Yellow-cheeked crested gibbon (Nomascus gabriellae), Hainan black crested gibbon (Nomascus hainanus), Cao-Vit black crested gibbon (Nomascus nasutus),

Southern white-cheeked crested gibbon (Nomascus siki) and Siamang (Symphalangus syndactylus; 2 subspecies: S. s. continentis, S. s. syndactylus).

Western Gorillas

Gorilla gorilla

There are two subspecies: the western lowland gorilla (G. g. gorilla) and the Cross River gorilla

(G. g. diehli).

Natural History

Cross River gorillas are found at the westernmost edge of the western gorilla range, in a small area along the Nigeria-Cameroon border. Western lowland gorillas range from Cameroon eastward to the Republic of Congo and southward to Angola. Western lowland gorillas are found in a variety of habitats, including primary and regenerating forests as well as lowland areas. Their distribution appears to be closely linked to the presence of terrestrial herbs, which are an important component of their diet.       

Western gorilla diet varies considerably by season. During the wet season, western gorillas eat a large amount of fruit; during the dry season, when fruit is less available, their diet consists primarily of fibrous vegetation and herbs. In comparison to eastern gorillas, western gorillas have larger day and home ranges, probably as a result of the higher fruit content of their diet.

Reproduction has not been thoroughly studied in the wild. It has been estimated that females give birth to an offspring every five years, but birth intervals can be greatly affected by seasons and food availability. They do appear to have longer interbirth intervals than mountain gorillas, probably as a result of their less consistent diet.

Like the other apes, western gorillas make both day and night nests. However, western gorilla nests are often on the ground or in the very low branches of trees.

Social Behavior

Western gorilla groups range from 2 to 32 individuals. Group size averages 10 individuals, generally including one adult male (silverback), three to four females, and multiple immature offspring. Most gorillas emigrate from their natal groups after reaching maturity. In all gorilla subspecies, silverback-female relationships are key to gorilla sociality. Because females do not meet until adulthood, they generally have very weak social bonds, as demonstrated by their extremely low rates of grooming and other affiliative behaviors. As a result, when the silverback dies, the females disperse to new groups rather than staying together. 

Communication between gorillas consists of grunts, barks, screams, hoots, and facial expressions.

Threats and Conservation

The western gorilla is considered Critically Endangered by the International Union for the Conservation of Nature (IUCN). The Cross River gorilla is the most critically endangered great ape subspecies, with an estimated 300 individuals remaining. Numbers for western lowland gorillas are estimated at 120,000 individuals; however this estimation has a large margin of uncertainty. Threats to western gorillas include: forest clearings, fragmentation, and degradation for agriculture, road building, and logging; hunting by private collectors and local people. Western gorilla populations have also been significantly affected by Ebola, which is estimated to have a 95% mortality rate in gorillas.

Eastern Gorillas

Gorilla beringei

The two subspecies are the eastern lowland or Grauer’s gorilla (G. b. graueri) and the mountain gorilla (G. b. beringei).

Natural History

Mountain gorillas reside in two known populations within the Democratic Republic of the Congo (DRC), Rwanda, and Uganda. The Virunga population lives in three national parks: the Virunga National Park (DRC), Volcanoes National Park (Rwanda), and Mgahinga Gorilla National Park (Uganda); the Bwindi population lives in Bwindi National Park in Uganda. Grauer’s gorillas only live in eastern DRC in the Kahuzi-Biega National Park and bordering Kasese region, Maiko National Park, Itombwe Forest, and North Kivu. The subspecies are geographically separated.       

In the Virungas, the mountain gorillas reside at the ecological extreme for the species: montane forest ranging from 2000 m to 4100 m. Bwindi and Grauer’s gorillas generally live in lower-altitude habitats (1,110 m to 2,600 m for Bwindi gorillas; 600 m to 2,900 m for Grauer’s gorillas). The high altitude (up to 4,100 meters) of the Virunga mountain gorilla habitat limits their diet to primarily herbaceous vegetation, as little fruit is available. Bwindi mountain gorillas and Grauer’s gorillas both range at lower altitudes and incorporate considerable fruit into their diet during the seasons it is available. As a result, ranging behavior varies between the subspecies. Virunga mountain gorillas have home ranges ranging between 5.5-11 km2; these values for Bwindi and Grauer’s gorillas are 20-40 km2 and 13-17 km2.

Females reach maturity at about eight years and the birth interval is about four years. Between the first sign of menstruation and conception, there is about a two-year sterility period. Mating outside of a group is rare.

Nests are built by adults and weaned young each night for sleeping. Unlike most other apes, mountain gorillas primarily nest on the ground.

Social Behavior

Group size ranges from 2-65 with an average group size of 10. Unlike western gorillas, eastern gorillas are known to form multi-male breeding groups, particularly in the mountain gorilla subspecies. In some groups up to 10 adult males have been observed to live together. This can provide for more group stability than found in western gorilla groups because there is a subordinate male to take over if the dominant male dies. Natal dispersal is observed in both males and females, although roughly 50% of Virunga male gorillas do not disperse. As with western gorillas, grooming and other social support is uncommon between females and female-female relationships are weak.

Communication is similar to western gorillas and consists of grunts, barks, screams, hoots, and facial expressions.

Threats and Conservation

Eastern gorillas are considered endangered by the International Union for the Conservation of Nature (IUCN). The Grauer’s subspecies is listed as endangered and the mountain gorilla is listed as critically endangered. There are currently 700 mountain gorillas remaining and this subspecies of ape is the only one known to be increasing. Because of the long civil war in DRC, conservationists to do not have a reliable estimate on the number of Grauer’s gorillas. The projected range is from 5,000 to 26,000 individuals. Threats to eastern gorilla survival include: hunting, war and political unrest, habitat loss and modification, and disease transmission from humans.

Orangutans

Bornean orangutan

Pongo pygmaeus

The Bornean orangutan is divided into three subspecies: the northwest Bornean orangutan (P. p. pygmaeus); the central Bornean orangutan (P. p. wurmbii), which is the largest subspecies, and the northeast Bornean orangutan (P. p. morio), which is the smallest subspecies.

Natural History

The Bornean orangutan resides on the island of Borneo in Central Kalimantan (Indonesia) and Sabah, West and East Kalimantan, and Sarawak (Malaysia) in peat-swamp forests and flood plains. Bornean orangutans enjoy eating high-energy, sugary fruits. They are opportunistic foragers, and thus they have very flexible diets that change with the seasons. When fruit and figs are not available, orangutans eat bark, leaves, gingers, and stems.      

Home ranges vary in size. Male home ranges are two to three times larger than those of females. Dominant males maintain relatively small home ranges.

Females reach maturity between ages 11 and 15 and give birth approximately every eight years. Once males become ‘flanged’, or develop cheek pads, they are mature and preferred as mates for matured females. Offspring are dependent for 7-10 years, which is the longest for any animal species other than humans.

It has been observed that some Bornean orangutans use leaves or a pile of twigs to shield themselves from the sun or rain. Despite this limited tool use observed in the wild, captive Bornean orangutans are very proficient tool users. Like the other apes, Bornean orangutans make night nests before going to sleep. The nests are arboreal and made of materials such as branches, leaves, and twigs.

Social Behavior

Orangutans, both Sumatran and Bornean, maintain loose communities or clusters of males and females. Mother-infant bonds are the strongest and weaken with the offspring’s age. Males either move to a new community or wander between communities once they have become independent. Flanged males do not tolerate each other, but they are tolerant of subadult males. Relatively high food abundance in some parts of the Sumatran orangutans’ range enables greater levels of sociality than has been observed among Bornean orangutans.

In both species, long calls enable adult males to notify females and other orangutans of their location over long distances. It is thought that the cheek pads on adult males help them direct their calls.

Threats and Conservation

Bornean orangutans are considered endangered by the International Union for the Conservation of Nature (IUCN). In 2004, it was estimated that there are between 45,000-69,000 Bornean orangutans. Although the habitats of the orangutans are technically protected, the majority of threats faced by the Bornean orangutans include: deforestation, logging and the production of timber, the production of palm oil, forest fires, and hunting.

Sumatran orangutan 

Pongo abelii

Currently only a single species of Sumatran orangutan is recognized.

Natural History

Sumatran orangutans live on the island of Sumatra in Indonesia and are most abundant in the forests of flood plains, alluvial bottomlands, and freshwater and peat swamps. Orangutans live best in areas with low human populations. Most Sumatran orangutans live below 1,000 meters. Current distribution is primarily determined by the availability of preferred fruits and human presence.      

Ranging patterns differ between Sumatran orangutans. There are three classes of ranging behavior: ‘resident’, ‘commuter’, and ‘wanderer’. Male home ranges are two to three times larger than female’s. Dominant males maintain relatively small home ranges.

Females reach maturity between ages 11 and 15 and give birth approximately every eight years. Once males become ‘flanged’, or develop cheek pads, they are mature and preferred as mates for matured females. Offspring are dependent for 7-10 years, which is the longest for any animal species other than humans.

Sumatran orangutans can be prolific tool users and have been documented to use multiple types of tools, primarily for extracting food and protecting themselves from sun or rain. Tool use is most prevalent in populations where food is abundant and thus permits larger associations and high levels of social tolerance. This suggests that orangutan tool use behavior is socially transmitted and represents an example of culture. Like the other apes, Sumatran orangutans make night nests before going to sleep. The nests are arboreal and made of materials such as branches, leaves, and twigs.

Social Behavior

Orangutans, both Sumatran and Bornean, maintain loose communities or clusters of males and females. Mother-infant bonds are the strongest and weaken with the offspring’s age. Males either move to a new community or wander between communities once they have become independent. Flanged males do not tolerate each other, but they are tolerant of subadult males. Relatively high food abundance in some parts of the Sumatran orangutans’ range enables greater levels of sociality than has been observed among Bornean orangutans.

In both species, long calls enable adult males to notify females and other orangutans of their location over long distances. It is thought that the cheek pads on adult males help them direct their calls.

Threats and Conservation

The Sumatran Orangutan is considered Critically Endangered by the International Union for the Conservation of Nature (IUCN). In 2002, it was estimated that only 7,300 Sumatran orangutans remained. Threats include: hunting, international trade, forest fires, forest fragmentation, timber production, and logging.

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