Apes: Hominoids

Scientific Name1

Common Name

Lesser apes


HYLOBATIDAE (hylobatids)


Hylobates sp.


Symphalangus sp.


Great apes


HOMINIDAE (hominids)


Pan sp.


Pan paniscus

bonobo, pygmy chimpanzee

Pan troglodytes

common chimpanzee

Gorilla sp.


Gorilla gorilla gorilla

lowland gorilla

Gorilla gorilla graueri

western highland gorilla, eastern lowland gorilla

Gorilla gorilla beringei

mountain gorilla

Pongo pygmaeus


Pongo pygmaeus pygmaeus

Bornean orangutan

Pongo pygmaeus abelii

Sumatran orangutan


This is a list of scientific and common names of species discussed in this chapter, not a comprehensive taxonomic list.

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--> 9— Apes: Hominoids Scientific Name1 Common Name Lesser apes   HYLOBATIDAE (hylobatids)   Hylobates sp. gibbon Symphalangus sp. siamang Great apes   HOMINIDAE (hominids)   Pan sp. chimpanzee Pan paniscus bonobo, pygmy chimpanzee Pan troglodytes common chimpanzee Gorilla sp. gorilla Gorilla gorilla gorilla lowland gorilla Gorilla gorilla graueri western highland gorilla, eastern lowland gorilla Gorilla gorilla beringei mountain gorilla Pongo pygmaeus orangutan Pongo pygmaeus pygmaeus Bornean orangutan Pongo pygmaeus abelii Sumatran orangutan 1   This is a list of scientific and common names of species discussed in this chapter, not a comprehensive taxonomic list.

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--> The apes are classified in the superfamily Hominoidea. The lesser apes (gibbons and siamangs) are placed in the family Hylobatidae. Great apes and humans are placed in Hominidae, but some would place the orangutan (Pongo), in a family by itself, Pongidae. Some recognize chimpanzees and gorillas, the two knuckle-walking African apes, as members of the same genus, Pan, but others prefer to keep the gorilla (Gorilla) separate to highlight the greater relationship of chimpanzees (Pan troglodytes) to bonobos or pygmy chimpanzees (Pan paniscus). The hylobatids, or lesser apes, are all specialized for brachiation (arm swinging). The siamang is roughly the same height as the gibbon with slightly less elongated arms, but it weighs nearly twice as much. Gibbons are all of similar structure with greatly elongated arms, hands, and fingers and are divided into species on the basis of pelage, vocalizations, and variations in throat-sac adaptations. All hylobatids are native to the rain forests of southeast Asian and Indonesia. They live in monogamous groups and are territorial frugivores. Capable of long flying leaps, swinging from hand to hand suspended beneath branches, they are extraordinarily graceful to watch. They also "sing" duets, and the calls are loud but melodious. These calls are analogous to bird calls in that they often advertise a defended territory. Their arms are so long that if they are forced to walk on the ground and brachiation is not an option, they must walk bipedally. The gibbon's thumb is unusual in that the metacarpal is free; this allows the gibbon to use this "extra" joint to fold the thumb across the heel of the hand in locomotion. Great apes are popular in zoological exhibits, and the chimpanzee is often the animal of choice in some research settings (NRC 1997b). The mountain gorilla, famous from numerous television shows about wild animals, has only rarely been seen in captivity; exhibitors almost always display the lowland variety. A third subspecies, the western highland gorilla (or eastern lowland gorilla), is also recognized in the wild. Orangutans all belong to a single species (Pongo pygmaeus ), but Bornean and Sumatran subspecies are recognized, and the orangutan species survival plan (SSP) insists that they be kept segregated. Hybrids are readily produced in captivity, but geographic separation prevents gene flow between the two subspecies in the wild. Although earlier systematists recognized four subspecies of chimpanzee, little effort has been made to segregate or even identify chimpanzee subspecies in captivity. (See also work by Morin and others 1992, 1994 on subspecies identification in Africa.) The bonobo is, however, a morphologically and behaviorally distinct species (Napier and Napier 1985; Susman 1984). Housing Adult gibbons and siamangs are not tolerant of other adults of the same sex for any long period, although large numbers of immatures can be safely housed

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--> together in the presence of an adult or adult pair (Bernstein and Schusterman 1964). Perhaps as a function of the large cage area necessary for their brachiating locomotion, relatively few gibbons or siamangs are found in laboratory settings, although exhibitions often feature these animals in settings that permit display of their graceful locomotion. Cages provided with horizontal supports that permit suspensory locomotion are well suited for these animals, and they will normally remain in high locations, descending to the floor only occasionally. They are not physically powerfully animals, and cages can be made of lighter material than required for Old World monkeys of comparable size. The great apes, in contrast, are extremely powerful animals with enormous hand strength. All three genera of great apes are commonly found in exhibits, but only the chimpanzee is found in laboratory settings in substantial numbers (Byrd 1977; Fritz and others in press; NRC 1997b). Exhibits generally maintain great apes in small groups in outdoor compounds provided with heated indoor shelters. The orangutan is generally regarded as semisolitary in the wild, and, although it will do well in small social groups in captivity, it might be wise to have only a single adult male in such a group. Adult male chimpanzees can be housed together (Alford and others 1995), and male gorillas that grow up together can be tolerant of one another. A few laboratories maintain chimpanzees in individual cages under biocontainment conditions. Even under these conditions, however, chimpanzees will benefit from visual and auditory contact with others (NRC 1997b; see also discussion below). Although chimpanzees and gorillas locomote primarily as quadrupeds, supporting their weight on the soles of their feet and knuckles of their hands, both are active climbers and often suspend themselves by their hands. Accordingly, cages should be tall enough to permit any ape to hang by the fingers without touching the floor. Among the great apes, orangutans are least suited to terrestrial locomotion, and they are generally quadrumanous, cautious, slow climbers in which diagonal limbs (e.g., right arm and left leg) move in synchrony as in quadrupedal walking (Hunt 1991). Although generally slow, orangutans can move very rapidly when alerted or during acts of aggression. They probably will profit the most from platforms, ropes, and hanging structures, although all apes will make good use of such furnishings (Fritz and others in press). All great apes construct sleeping nests in the wild and will use straw, cloth, and any other suitable materials to make nests in captivity. Young apes appear to need to practice this skill lest they fail to make nests as adults (Bernstein 1962, 1967). Young apes, and especially orangutans, enjoy crawling inside cloth bags, barrels, and similar containers. Such items stimulate much play, but as with all such objects, care should be taken to avoid items that could be dangerous to the animals through ingestion or entanglement. When adequately adapted, apes can tolerate temperature extremes, as can Old World monkeys, but shelter from direct sun, wind, rain, and temperature extremes should be available, as recommended in the Guide (NRC 1996) and

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--> required by Animal Welfare Regulations (9 CFR Subchapter A). Because their black bodies absorb heat from direct sun rays, there is potential for chimpanzees and gorillas to suffer from heat stroke at relatively mild temperatures, although chimpanzees are routinely maintained outdoors in the southern United States with temperatures in the shade routinely above 38°C (100°F). Chimpanzees tolerate cold quite well for short periods but bonobos and lesser apes require shelter even at air temperatures of 10°C (50°F) and above. All animals should have access to indoor ''night quarters." Chimpanzees often engage in charging and drumming displays, which intimidate cagemates and visitors and can weaken cage structure. Inanimate objects and other group members are sometimes hit during these displays. Under these conditions, a door for retreat into a separate area is particularly helpful. Barrels are provided to enable this species-typical behavior in some facilities and constitute an effective and less-expensive option than repairing damage to caging or handling injuries to other animals. Proper design might be more important than space itself in the design of ape quarters (Fritz and others in press; NRC 1996, 1997b). Chimpanzees in social groups will make use of separate areas. The opportunity to join and leave a social group at will during times of tension is beneficial for animals that might be picked on during noisy displays. Chimpanzees have well-developed mechanisms to restore social harmony (de Waal 1989), but the opportunity for brief voluntary separation is helpful. Ideally, housing permits the full range of locomotor expression, and socially housed chimpanzees enjoy space to play. Areas that are divided by a large obstacle provide a circular arena for such games as chase. Vertical space is also very important to apes, and one or two areas a few meters (9–15 ft) high, permitting a broad view of the surroundings, are favored locations (Traylor-Holzer and Fritz 1985). If possible, outdoor areas should have other than concrete floors, preferably natural grasses or bedding. A deep straw, pine– or cedar-bark, or woodchip cover 25–30 cm (10–12 in) deep has worked well in outdoor enclosures (Brent 1992; Rumbaugh and others 1989) and decomposes into a medium not conducive to insects. The ground cover stays clean as long as all fecal and urine-soaked material is removed daily. Most agree that the best enrichment for a chimpanzee is another chimpanzee. Even in social groupings, however, attention should be given to the inanimate part of their environment. Attempts by zoological and research institutions have demonstrated the value of providing a wide assortment of furnishings for chimpanzees' use and amusement, including providing them with large uprooted trees (Maki and Bloomsmith 1989); "termite" feeders (Maki and others 1988); television or live-action video of other chimpanzees (Rumbaugh and others 1989; see also Platt and Novak 1997 for use in macaques); puzzle feeders (Maki and others 1989); traffic cones (Fritz and Howell 1993a); nesting materials, such as woodchips (Brent 1992), straw, cloth, or shredded paper (Fritz and others in press); and novel methods of providing food treats (see also Fritz and Howell

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--> 1993a; Rumbaugh and others 1989), including ice cubes with or without flavoring (Fritz and Howell 1993b). When social grouping is not possible, attention must be given to the needs of the singly housed animal. These needs change with age, health, and experience. Immature chimpanzees respond positively to the opportunities to play or be groomed by a familiar human (Fritz and Fritz 1985; Reisen 1971; Shefferly and others 1993), and can prefer social interaction to food (Mason and others 1962, 1963). Older animals, too, benefit greatly by interactions with known caregivers (Baker 1997; Fritz and Howell 1993a; Laule and others 1992, 1996). Dogs also provide infant chimps with a playmate (Black 1992; Thompson and others 1991). Even when single housing is required, such as for biocontainment, much can be done to enrich the environment (Brent and others 1989; Fritz and others 1997; Lambeth and Bloomsmith 1992; Nadler and others 1992). These and many other enrichment options discussed throughout this report demonstrate relatively simple strategies to enrich the lives of these animals. Not the least of these approaches is positive human interaction (Fritz and Howell 1993a; Mason 1965). See also NRC (1997b) and the chapter in the Universities Federation for Animal Welfare handbook (Fritz and others in press) for additional discussion of chimpanzee biology, behavior, housing, and enrichments. Nutrition Apes in the wild have a diverse diet that is based on fruits and selected leaves and stems but can also include roots, bark, nuts, insects, bird eggs, and small mammals (Goodall 1963, 1986; Napier and Napier 1985). The natural diet of gorillas includes a greater percentage of fibrous plants than commonly eaten by other apes. In captivity, if necessary, apes can be maintained on a commercial diet specifically prepared for primates; however, they seem to relish a more varied diet that includes fruits, vegetables, and treats. If apes are fed only natural foods, a wide variety of items to ensure adequate protein intake, as well as vitamin and mineral supplements, should be provided. The nutritional management of nursery-reared infant chimpanzees have been reviewed by Fritz and others (1985). Foods may be presented in clean feeders, cut into small pieces and widely scattered, or left whole and unpeeled to extend feeding time (Bloomsmith 1989). Also, spreading selected treats, such as nuts and grains, in bedding or grass will give apes an opportunity to forage. If apes are housed in social groups, it is necessary to provide enough food so that the most timid animal in the group can get its full allotment, or positive reinforcement training can be used to overcome severe competition at mealtime (Bloomsmith and others 1994). For enrichment, such food items as honey, mustard, peanut butter, raisins, and nuts can be placed in puzzle or foraging devices (Maki and others 1988, 1989). Some moderation should be practiced in the use of high-calorie treats.

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--> Coprophagy, regurgitation, and reingestion are common in captive apes (Fritz and others 1992b; Howell and others 1997; Morgan and others 1993) and to some degree in wild chimpanzees (Goodall 1968, 1986). It appears that these practices are more frequent when animals are insufficiently occupied, yet providing forage in deep bedding has been implicated as a contributing cause of coprophagy in some animals (Fritz and others 1992). These practices are difficult to eliminate, but the best recommendation possible at present is to provide the animals with a rich social and physical environment and keep indoor areas as free as possible of feces. Social Behavior Despite the sometimes solitary nature of wild orangutans, all great apes profit from social companionship. Proper social stimulation is crucial for normal development of infant and juvenile animals (Fritz and Howell 1993a; Mason 1965, 1991; Mason and others 1962, 1963), and the adverse consequences of early social restriction are only somewhat ameliorated by later rehabilitation efforts (Davenport and Rogers 1970; Davenport and others 1973; Fritz 1986, 1989; Rogers and Davenport 1970). The advice on early rearing given in Chapter 3 also applies in the case of the apes. Mother-reared female apes generally become competent breeders and mothers and will provide adequate care for their infants in the presence of their usual companions, including their adult male partners. Sometimes the appearance that a mother is not attentive, or is abusive, to her infant stimulates caregivers to intervene. Often, however, these attentions are unneeded or even harmful, and personnel trying to protect infants from the attention of other group members (or from lack of attention from the mother) might do more harm than good by interfering in such situations. One common instance of this is when newborn chimpanzees are not observed to nurse for the first 48 hours or more. If the infant is well hydrated and reasonably active it probably means that it is nursing at night or at other unobserved times, and intervention is not warranted. Males reared in social groups containing cycling females, infants, and adolescents usually develop normal copulatory skills and paternal behaviors. Socially restricted or nursery-reared males, however, often are inadequate breeders and parents (Fritz 1986). Adult male gorillas display remarkable gentleness in wrestling and play-fighting with older infants and young juveniles. An issue of concern in today's biomedical chimpanzee colonies is how to sustain male copulatory skills without producing offspring. Owing to the burgeoning biomedical chimpanzee population (NRC 1997b), most chimpanzee-colony managers are attempting different strategies to accomplish this goal, including the use of Norplant® in females, vasectomizing some males that can serve as role models for prepubertal males, and separation of the sexes. It is probably too early to recommend one strategy over the others, for each has merits

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--> and problems. For example, the duration of efficacy of Norplant® in chimpanzees is not known but could be considerably shorter than in women (Mike Keeling, personnel communication), vasectomizing chimpanzees is more difficult in chimpanzees than in other primates in which it has been accomplished, and separation of the sexes can lead to insemination (or bitten penises) through wire cages and sexual frustration and aggression in males housed near cycling females (Alford and others 1995). In one recent case in which young adolescents of both sexes were housed together, a 5 1/2-year-old male inseminated four older females with which he was housed; this is the youngest documented male to sire offspring (International Species Information System, ISIS personal communication to the committee), and it shows the risk posed by opposite-sex housing of even young adolescents. Reproduction and Development The apes all show regular menstrual cycles at intervals of about 5 weeks. Chimpanzee females develop huge (3–5 L) perineal swelling, with ovulation immediately after reduction in swelling, but only minor changes in the labia might be detected in gorillas and orangutans and none in lesser apes. Gestation periods are 7–8 months, and a single infant is generally born, although twins and even triplets have been observed in chimpanzees (Greissmann 1990). During the first half-year of life, the infant ape has essentially continuous body contact with its mother; it begins to engage in exploration, food-getting, and social interaction beyond its mother during the second half of the first year. Normally, mothers do not allow others to hold their infants for the first few weeks of life. If possible, infant apes should remain with their mothers and have contact with other members of their own species. If infant apes require removal from their mothers, it is essential that they receive around-the-clock care from familiar caregivers who are sensitive to their needs for contact and motion (Fritz and Fritz 1985). Infants are highly sensitive to sudden movements, such as being picked up or laid down quickly. Transfer of an infant from person to person should be slow, and infants should not be subjected to forced handling by strangers. They need to be fed on demand (Fritz and others 1985). Past practices of placing a mother-separated infant in a cage and taking it out only for feeding and cleaning are to be discouraged because they contribute to social and cognitive developmental problems. When care was provided by a large and changing cadre of people, specific attachment to a psychological mother was precluded. Under those conditions, great apes do not develop normal emotional responses and are likely to become unpredictable and dangerous both to human beings and to other apes. Breeding takes place regularly in small groups, and there is some evidence that a single gorilla female in captivity, as well as in the wild, reproduces more poorly than if she is kept with at least one other female. Although chimpanzee

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--> males might compete for a receptive female, most competition consists of noisy display. Gibbons and siamangs will breed when maintained as pairs. Males are reported to show care of older offspring (they might sleep with a juvenile and spend much time with it) after new infants are born. These animals do well in family groups. Infant apes can be nursed for 3 years or longer, and interbirth intervals of 4 years or more are not unusual (Fritz and others 1991). Development to full adult size can take 9–10 years in gorillas and even longer in orangutans. One curious observation in orangutans is that the presence of a fully adult male inhibits the development of cheek flanges and other secondary sex characteristics, but not fertility, in maturing males (Kingsley 1980; Rodman 1988). As with New World and Old World monkeys, sexual maturity can precede full physical size, and pregnancies have been reported in exceptional females as young as 6 or 7 years old. A period of adolescent sterility might follow puberty and first menstrual cycling. Females also reach sexual maturity and full body size several years before their male age peers. Genital rubbing between bonobos of every age-sex combination has been observed in natural groups. This should be regarded as part of their social repertoire, rather than sexual behavior, and it neither enhances nor decreases reproductive activity (Thompson-Handler and others 1984). Cognition Although gibbons and siamangs have not been noted for advanced cognitive capacities, great apes exhibit remarkable complex learning and tool-using skills. They readily develop concepts in formal training, and orangutans and chimpanzees can recognize themselves in mirrors and in televised images (Gallup 1977, 1982; Lambeth and Bloomsmith 1992; Menzel and others 1985). Enrichment devices to stimulate activity will occupy much of the time of captive great apes (Bloomstrand and others 1986; Paquette and Prescott 1988; Rumbaugh and others 1989). They interact with objects creatively and will spend substantial amounts of time with simple tools and sticks. They like fabrics—such as squares of carpet, various types of cloth, or blankets—for examination, destruction, and use as nesting materials (Bernstein 1962, 1967). Chimpanzees also become adroit in performing a wide variety of complex video tasks, using a joystick to control events on a monitor. If they are reared from birth in an environment where humans speak to them communicatively and extensively, there is evidence that at least bonobos and chimpanzees can understand many requests. That can be helpful, for example, when an attendant asks a chimpanzee to trade a cage lock or piece of equipment for food (Laule and others 1992). If chimpanzees are allowed to see and hear real-world events on video moni-

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--> tors while they view the same events directly, they are likely to "discover" that monitors can portray parts of the world that they otherwise cannot see (Bloomsmith 1989). For example, chimpanzees can garner important information from video monitors about the locations of foods and incentives and about the course of activities in areas beyond their view (Menzel and others 1985). Chimpanzees can come to prefer watching specific video-taped recordings, especially those of other chimpanzees they know, but there is little reason to believe that they profit from watching ordinary television programming other than nature films on conspecifics. They might attend to programs showing vigorous human interactions, such as dancing and sports (e.g., wrestling, boxing, and football) (D.M. Rumbaugh, unpublished data). Providing television sets for animals in laboratories and on exhibit has a certain appeal to humans, but benefits to the animals are dubious. Despite their impressive cognitive abilities and interest in a wide variety of puzzles and cognitive challenges, there is as yet no way to assess a "need" for intellectual exercise in great apes. Ordinary social living in a well-designed enclosure might provide chimpanzees and other great apes all the intellectual stimulation that they require. Although attempts at enrichment should certainly be directed at singly caged animals in restricted environments (Nadler and others 1992), those in social groups also benefit greatly from an enriched environment. Personnel Caregivers should be sensitive to apes as individuals. Apes often do not trust unfamiliar people, so new caregivers should be introduced systematically and gradually. In this way, both humans and apes learn what to expect from one another, and experienced personnel recognize the needs of their charges (Baker 1997). Feeding time is a very important time of day, and feeding practices should be such as to encourage caregiver-animal communication. Feeding and cleaning practices can serve to establish good relationships between caregivers and apes that, in turn, enrich the apes' lives and also inform the caregivers regarding the animals' behavior and physical condition. Not only should personnel be trained and experienced in the behavior of apes, but it is imperative that they be trained in safety. Great apes are very powerful, active, and sometimes devious. Primates in general will harm people only in defense or in reaction to a threat, but a chimpanzee's aggressive actions are unpredictable and often seem premeditated. Such serious injuries as loss of fingers, bite and scratch wounds, and lacerations have been suffered by people working with apes. Chimpanzees should be treated with respect throughout their development. They have long memories and will recognize a favored or disfavored human after several years of separation. Personnel should be continually reminded of established safety procedures. Cages should be designed to prevent the apes from reaching outside the cage.

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--> Gibbons are capable of very rapid movement and can grab and bite with lightning speed. Even the bonobo, the smallest of the great apes, has enormous digit strength and can pull objects from or hold onto a human of much greater body size. Great caution should be used when handling unsedated apes, especially after they attain a weight of 12–15 kg (26–33 lb). Even the most reliable animals have the potential for causing serious harm to humans with whom they are in direct contact. In addition to a general occupational-health program for people working with primates, consideration should be given to immunizing ape caregivers against hepatitis B, poliomyelitis, and influenza viruses, as well as to those currently recommended by CDC for health-care workers. Personnel with colds should not have contact with apes or they should at least wear industrial-level respirators covering the nose and mouth. Apes are susceptible to colds, and an infection with Streptococcus pneumoniae can be fatal. Several of the great apes learn to spit and throw. Chimpanzees can spit more than a pint of water and throw feces with great accuracy. Such behavior is directed at disfavored people and strangers and sometimes is used merely to provoke a responsive person. A trusted human can usually "talk" an animal out of such behavior by a calm, gentle approach, but this is not always successful. The response of a human when being spat on might inadvertently serve to "reward" the ape and increase the likelihood of its spitting in the future. Veterinary Care Daily health observations by experienced persons are critical to the physical well-being of apes. Persons knowledgeable about an ape's particular personality and behavior might become aware of illness before traditional clinical signs are apparent. Veterinarians should strive to work as a team with all personnel who have contact with the apes (e.g., behaviorists, caregivers, technicians, and investigators) to develop a program to monitor the condition of the animals. Training time might be protracted, but the reward of less stress for the animals and humans can be very worth while. During treatment, drugs, especially liquid formulated ones, can be masked in flavored gelatin drinks or fruit juices, and an animal might readily accept even unusual items when they are offered by a favored person. A squeeze cage might be used as a last resort when there is no other safe way to deliver injectable medications. It is far preferable to train chimpanzees to present an arm or thigh against a wire-mesh cage wall (Laule and others 1992, 1996). They often accept injections for a small treat afterwards.