The Great Apes Research Paper
Jacob Mamiye 12/6/2014
Anthropology Professor Mwaria
Social Organization, Characteristics and Behaviors of the Great Apes
1 Compare and contrast the social organization of the great apes (chimps, bonobos, and gorilla’s orangutans) and savannah baboons. What accounts for these differences?
The social organization of baboons is one of the most intensely studied of the primates. There is only one defined level of social organization in savanna baboons, the stable group of several dozen individuals. This group is defined by tending to not break into any recurring subgroups and not merging with neighboring groups. In Papio hamadryas, (desert baboons), both internal organization and relations with other groups resembles that of savanna baboons. Hamadryas may spilt into one male units that eat separately during the day but may sleep on the same rocks at night. Several bands of baboons may merge to sleep on the same rock at night forming a troop. Clearly a troop has …show more content…
many separate properties with bands that think independently but all work together in common defense.
Basic units (small groups) are defined by three basic principles that distinguish their existence in all primate societies: the members of a unit stayed together more closely than they stayed with the rest of the troop, the frequency of social behavior was significantly higher among the unit members than between members and outsiders and that these characteristics remained the same during the duration of the observable study. Regarding spatial coherence between baboons’ social units, individuals were usually four times closer together than they were to the rest of the individuals in the troop. Permanence of units can vary however and some parties of animals are more prone to breaking away such as playful youngsters or subadult males grooming each other.
Among these “detachable parties” the “one male unit” is only unit that stays together continually. “Out of six units studied, none changed the leader.” (Kummer 22) This may be a trait that allows for more trustful relationships in political, sexual and spatial conflicts. The compositions of these detachable parties include only one leading adult male.
There have been studies that show that all sexually mature females in a given troop reside within one-male units. Some males of all ages may choose to live outside of the male unit but within the framework of the troop. It is obvious that these individuals are at a disadvantage since they are not as bonded as the other units are.
Occasionally, subadult males can join in the one-male units as followers that flank the sides of the group. These younger males are sometimes groomed by the adult females of the group. During troop walks, almost all social behavior is restricted except for spacing. In all primate species spacing plays a crucial role in the social intentions between individuals. For baboons, long walks restrict all other obvious social behaviors. Social contacts may disappear altogether during the duration of the walk and need to be restated constantly.
Violence is inherent in the baboon troops and is a common medium of stating dominance for males. During treks, male leaders keep constant vigil on their females and respond with threats when they lag behind or get too far away. This is essential for mating rights since females are not choosey and will copulate when they come into heat with any male.
Male threats can range from the mildest: a stare with raised eyebrows, to increasingly severe punishments. “Neck bites” or bites to the back are the most intense of the consequences females may face when they stray. Immediately following the bite, the female will stick closely to the male. These fights are neither frequent nor destructive and a bite to the neck hardly ever produces a bleeding wound. An article called Apes of Wrath explains, “The neck bite is ritualized-the male does not actually sink his razor-sharp canines into her flesh-but the threat of injury is clear. By repeating this behavior hundreds of times, the male lays claim to particular females months or even years before mating with them.” (Smuts) When one unit leader’s female is threatened by other males he will protect her by throwing his arms around her in a hug or hunching over her body while threatening the opponents.
It is respected and understood that males will only breed with females belonging to their own unit. Strikingly, when a female is in estrus, a male will pursue the female and substitute threats for social grooming. Even in a society governed by violent displays of dominance, males will always do what they can to have sex. Grooming thus has important significance to baboons and social grooming takes up the majority of an adult baboon’s time. Grooming also strengthens social bonds in most primate species.
Chimpanzees are by far the most studied primates and possibly the most understood. Observations made by Jane Goodall in the 1960s and 1970s forever changed the way we view these animals as not only apes but as beings with capacity for intelligence and culture.
Chimpanzee social structure is largely similar to that of baboons as both live within a unit-group. This group is multi-male and multi-female and semi closed to outsiders. Average groups can range in populations of 20-105 individuals. The Mahale Mountains support the highest population density of the “eastern race of chimpanzees in Tanzania.” (T. Nishida 25) 30% of the 2000 individuals live around Mahale.
A unit group of chimpanzees is prone to splitting into many subgroups or parties just like that of savanna baboons. Unlike the baboons however the only stable units are those comprised of others and their infants. The separate groups may act individually but follow a general pattern of movement seasonally north and south within their respective ranges. Although each part may seem to move randomly, the body of the whole “community” moves relatively as one. This drive is usually a result of ripening or abundant fruit. In one season almost all groups converged into a single square kilometer to feed on the abundance of Garnacia fruits. (Nishida 26)
Adult males tend to gather together in groups and groom. They show stronger social bonds than those between adult females or between adult males and females. (Kawanaka 1984) Male bonding is used primarily to facilitate the defense of their communal territory. Within the group there is a “linear form of dominance hierarchy.” (T Nishida 29) If a group has many males it can be difficult to observe the dominance between all individuals. In one study however, male chimpanzee groups fell into four categories of rank: alpha, high-ranking, middle-ranking and low-ranking individuals. Furthermore there is inherent reluctance in males to obey higher ranking members. Males may also avoid rivals unless accompanied by their own allies. Food sharing usually follows the basic line of hierarchy as does mating.
Male-female relationships differ greatly than those exhibited between males. If a female is not in estrous and a wide-ranging male arrives, he will sniff her genitals to glean her sexual state. Amazingly if the female is in estrus a male is more likely to groom her than if she was not. This is a clever tactic to win the hearts of receptive females.
Female-female relations among chimpanzees is a rather vague topic. Dominance is presumably based on age and tenure in a group. Sometimes females may form coalitions to unite against older adolescent males who display charge against them or against a male who bullies one of them. New (immigrant) females who give birth are quickly enmeshed with the community thanks to social bonding. Rarely, a new female will be rejected by the group and a female coalition could be constructed against her.
Hierarchy is clearly demonstrated during the feeding of meat which is a crucial and highly prized source of nutrients such as protein. Male animals starting with the most dominant snatch up the carcass and take the first picks then the meat goes to mothers and other subordinate males. If a juvenile is orphaned it is likely that it will not get any meat. The dominance asserted by male chimpanzees also is expressed in inherently violent acts. Jane Goodall’s observations of the chimpanzees of Gombe, depict a violent streak that chimps can share. At one point, the chimpanzee group she was studying broke off due the human interaction. Over the course of a few months one half of the split group systematically hunted and killed the members of the other group. War is obviously not a uniquely human trait.
Bonobos were often referred to as “pygmy chimps” due to their similar appearance and slightly smaller build. This is misleading since bonobos are a completely different species that show different behaviors, different reproductive patterns and even different autonomy. Bonobos live in a remote region south of the Zaire River in the Democratic Republic of the Congo. (Jurmain 147) They are to this day the least studied of the great apes. Since their recognition as a separate species in 1929, there has been many field observations of the species which has provided unique insight into their social structure. Like the chimpanzee, the bonobo social structure is fluid and in both species, the members of a large community do not travel and forage all together rather they form smaller bands which can change in composition. “The difference is that band of adult-male chimpanzees are quite common, but this is not true of bonobos.” (de Waal 180) In bonobos, the strongest attractions are between adult females and between the sexes. Bonds between males are relatively weak. “Hence the bonobo’s society differs fundamentally from that of the chimpanzee, with female bonobos taking a much more central positon.” (de Waal 180)
Males refrain from gathering and sharing food together as this causes tension however females show no such behaviors. Meat is a part of bonobo diet and although the males are the first to take the spoils they gingerly give portions to the females throughout the day. Sex plays a part in dining by forming cohesive bonds that form between members of hunting parties. Females unlike those of most other primates are almost continuously receptive and are willing to mate through much of their monthly cycles. This in turn leads to a new behavior amongst the animals that sex can be used as a medium for communication and bond forming much like social grooming.
In fact, “females not only mate with males but have sexual exchanges among themselves.” (de Waal 182) This sexual behavior fosters their own concept of “make love, not war.” These observations reveal a highly erotic lifestyle of bonobos. Bonding through sex may avoid competition among males and ease tensions with neighbors. During hunts and territorial displays, males must cooperate and sexual tensions may reduce effectiveness as a group. Thus the females of a group are divided among males in a stable arrangement. These pair bonds made through sex are not a sign of monogamy and males will accompany many different females forming bonds more cohesive than that of most other primates.
The bonobo is also well known for its correlations with many aspects of both behavior and anatomy with humans. Unlike chimpanzees, bonobos are much more comfortable standing upright. Their backs are much straighter and their heads sit more vertically on their spinal column. They are commonly bipedal and walk with a similar gait to that of humans. Also their sexual behavior mimics that of our own which is incredible and provides insight into early hominids.
Orangutans are the only species of Great Apes in the Genus Pongo and lives in a region that is substantially climatically and geographically different. Unlike the other great apes, the orangutan is a rainforest dwelling species adapted for life in the tree canopy. In the forests of Sumatra and Borneo there is a very different and lacking social structure. Orangutans spend most of their lives in solitude or with their mothers until they are grown. There are no definable characteristics that would suggest leadership as most social behavior especially grooming is rare.
The dominance within societies of orangutans is patriarchal and there is a hierarchy among males in a region. Yet it is also apparent that orangutans follow very different unsocial behaviors. Although most of these primates are solitary they nevertheless do communicate with other members of their species. Their calls are mainly to assert dominance over territory- crucial in a forest environment. Unlike other foresting apes such as the lesser apes (hylobatids) males and females are hardly ever seen together. The most common of semi-social units are “individual females with their dependent youngsters, lone adult and subadult males, and various small groupings of adolescents or singletons. Mother/young units and older youngsters sometimes join temporarily…” (Tuttle 255) Captive orangutans show very different approaches to social behavior and are much more socially interactive like the other great apes. However, in the wild it is questioned why orangutans become so solitary.
It is known that orangutan infants are very social and are dependent on their mothers for shelter and milk. Mothers take care of infants for its first two years. By the third year it learns to construct a nest and becomes increasingly playful and inquisitive around the same time. In the next few months the baby is slowly weaned from its mother’s milk. As a juvenile, orangutans between five and six years old become indifferent and inattentive to their mothers and although they stay within the same vicinity they start to engage in distinct activities by themselves. By the age of seven they are seldom groomed and lose their strong social bonds. This marks the beginning of their wandering lifestyle through the forests alone.
Socially, these primates lack group cohesion yet territorial instincts are very important to all adult individuals. The lack of social organization leads to a new need to not only maintain boundaries but to assert dominance and attract mates. To overcome these challenges proposed by distance, the orangutan is the third loudest primate in the world after howler monkeys and the Indri lemur. The orangutan’s calls vary like that of many primates and can travel up to two and a half kilometers through the densely packed forests of Borneo and Sumatra. The most studied vocalization of Pongo is the astounding “long call” which is only issued by adult males in their prime. It begins as a deep rumble with a vibrato (wavering notes) and increases to a deafening roar. Long calls are not common and in one study only one individual (old) male issued a call only twice a month. A different area of forest held a very powerful dominant adult male who issued calls three to four times a day. These calls also seem to hold display significance as over 20% of long calls are issued after males break branches and directly before they copulate. It is thought that the calls also “serve… to space adult males in the forest [and] attract sexually receptive females to the caller.” (Tuttle 22)
Mountain and low-land Gorillas have a unique social structure and a behavior that is beautifully suited to their environments. The mountain Gorillas live in an alpine/bamboo forest habitat local to the Virunga Volcanoes range in Africa. The separate peaks of Kivu, Mfumbiro, Birunga and Kirunga volcanoes are their primary homeland. The size of natural populous groups ranges from two to thirty individuals. An average group size is most probably six and seventeen animals. At one location where the animals aren’t hunted and there is an abundance of food the group size remained considerably higher.
In 1963, George B. Schaller became the first scientist to habituate mountain gorillas to the presence of humans. His research is invaluable and explains the majority of social group composure and traveling patterns. The composition of Gorilla groups are relatively constant and contain at least one silverbacked (dominant) adult male, one or more females and a variable number of youngsters. “More than one silverbacked male was found in five of the twenty-seven observable groups in the year 1959. In all five of these groups there were more than ten members. Females usually outnumber silverbacked and blackbacked males. In one location, Kabara, the average group “consisted of 1.7 silverbacks, 1.5 blackbacks, 6.2 juveniles and 4.6 infants.” (Schaller 104)
Studies on Ugandan Mountain Gorillas reveal that large groups sometimes divide into smaller subgroups with irregular compositions and then reunite later. Also these same groups contained wandering silverbacks that appeared to be lone males. These single male units were seen stumble into two of the stable groups and were accepted so long as the resident silver back male was dominant. When other silverbacks are present the hierarchy formed is linear.
Inter group encounters are not uncommon since gorilla territories zones tend overlap. Dominance can be physically asserted with charging displays, branch shaking, low calls and especially chest beating which can be heard from afar. Despite seeing charging and glaring warnings by dominant males during group encounters, Schaller concluded that gorillas are not territorial. “Usually members of different groups ignored one another and occasionally they mingled peacefully for several minutes before moving on.” (Tuttle 291) Still, different groups were not as tolerant of their neighbors. Like all animals, coexistence can be affected by abundance of resources and can change seasonally.
The dominant silverback male is the heart of a cohesive group while other less dominant individuals keep their respectful distance on the periphery. The silverback tends to lead the group through the movements of daily activity such as when to forage and travel, resting and nesting. The females in the group rely on his protection. When traveling as a group the silverback stays at the leading frontal position but if a threat is detected he drops to the rear of his group to protect them from behind. Gorillas solemnly directly attack the threat. When an attack is provokes the individual will lunge forward make brief contact and retreat.
Cohesiveness of the group is thought to be maintained not by social grooming or sex.
Schaller reported that, “Karbara gorillas rarely groomed and that grooming was never reciprocal.” (Tuttle 293) Instead grooming was solely used to remove their body of irritants they themselves could not reach- similar to the way a human can ask someone to scratch their back. Females are the only individuals inclined to grooming (only the infants). Blackbacked males never groom and females hardly ever groom each other. Youngsters like all the primates noted are playful. Play bouts observed are brief periods less than 15 minutes long and do not result in fights or arguments. Observations made by Dian Fossey yielded more information on behavior since she created more intimate bonds with her study group in the Parc De Volcans Mountains. She confirmed that gorillas lived their life in tranquility with an absence of inherent violence. So like the bonobos, gorillas expose the gentle nature of the great
apes.
Bibliography
Kummer, Hans. Social Organization of Hamadryas Baboons. A Field Study. University of Chicago Press, Chicago, 1968. Print.
Waal, F. B. M. De. Peacemaking among Primates. Cambridge, Mass.: Harvard UP, 1989. Print.
Nishida, Toshisada. The Chimpanzees of the Mahale Mountains: Sexual and Life History Strategies, Tokyo: U of Tokyo, 1990. Print.
Schrier, Allan Martin, and Harry F. Harlow. Behavior of Nonhuman Primates: Modern Research Trends. Vol. 4. New York: Academic, 1965. Print.
Tuttle, Russell H. Apes of the World: Their Social Behavior, Communication, Mentality, and Ecology. Park Ridge, N.J., U.S.A.: Noyes Publications, 1986. Print.
Schaller, George B. The Mountain Gorilla; Ecology and Behavior. Chicago: U of Chicago, 1963. Print.
Jurmain, Robert. Essentials of Physical Anthropology. 9th ed. Belmont, CA: Wadsworth, 2013. Print.
Anthropology Professor Mwaria
Social Organization, Characteristics and Behaviors of the Great Apes
1 Compare and contrast the social organization of the great apes (chimps, bonobos, and gorilla’s orangutans) and savannah baboons. What accounts for these differences?
The social organization of baboons is one of the most intensely studied of the primates. There is only one defined level of social organization in savanna baboons, the stable group of several dozen individuals. This group is defined by tending to not break into any recurring subgroups and not merging with neighboring groups. In Papio hamadryas, (desert baboons), both internal organization and relations with other groups resembles that of savanna baboons. Hamadryas may spilt into one male units that eat separately during the day but may sleep on the same rocks at night. Several bands of baboons may merge to sleep on the same rock at night forming a troop. Clearly a troop has …show more content…
many separate properties with bands that think independently but all work together in common defense.
Basic units (small groups) are defined by three basic principles that distinguish their existence in all primate societies: the members of a unit stayed together more closely than they stayed with the rest of the troop, the frequency of social behavior was significantly higher among the unit members than between members and outsiders and that these characteristics remained the same during the duration of the observable study. Regarding spatial coherence between baboons’ social units, individuals were usually four times closer together than they were to the rest of the individuals in the troop. Permanence of units can vary however and some parties of animals are more prone to breaking away such as playful youngsters or subadult males grooming each other.
Among these “detachable parties” the “one male unit” is only unit that stays together continually. “Out of six units studied, none changed the leader.” (Kummer 22) This may be a trait that allows for more trustful relationships in political, sexual and spatial conflicts. The compositions of these detachable parties include only one leading adult male.
There have been studies that show that all sexually mature females in a given troop reside within one-male units. Some males of all ages may choose to live outside of the male unit but within the framework of the troop. It is obvious that these individuals are at a disadvantage since they are not as bonded as the other units are.
Occasionally, subadult males can join in the one-male units as followers that flank the sides of the group. These younger males are sometimes groomed by the adult females of the group. During troop walks, almost all social behavior is restricted except for spacing. In all primate species spacing plays a crucial role in the social intentions between individuals. For baboons, long walks restrict all other obvious social behaviors. Social contacts may disappear altogether during the duration of the walk and need to be restated constantly.
Violence is inherent in the baboon troops and is a common medium of stating dominance for males. During treks, male leaders keep constant vigil on their females and respond with threats when they lag behind or get too far away. This is essential for mating rights since females are not choosey and will copulate when they come into heat with any male.
Male threats can range from the mildest: a stare with raised eyebrows, to increasingly severe punishments. “Neck bites” or bites to the back are the most intense of the consequences females may face when they stray. Immediately following the bite, the female will stick closely to the male. These fights are neither frequent nor destructive and a bite to the neck hardly ever produces a bleeding wound. An article called Apes of Wrath explains, “The neck bite is ritualized-the male does not actually sink his razor-sharp canines into her flesh-but the threat of injury is clear. By repeating this behavior hundreds of times, the male lays claim to particular females months or even years before mating with them.” (Smuts) When one unit leader’s female is threatened by other males he will protect her by throwing his arms around her in a hug or hunching over her body while threatening the opponents.
It is respected and understood that males will only breed with females belonging to their own unit. Strikingly, when a female is in estrus, a male will pursue the female and substitute threats for social grooming. Even in a society governed by violent displays of dominance, males will always do what they can to have sex. Grooming thus has important significance to baboons and social grooming takes up the majority of an adult baboon’s time. Grooming also strengthens social bonds in most primate species.
Chimpanzees are by far the most studied primates and possibly the most understood. Observations made by Jane Goodall in the 1960s and 1970s forever changed the way we view these animals as not only apes but as beings with capacity for intelligence and culture.
Chimpanzee social structure is largely similar to that of baboons as both live within a unit-group. This group is multi-male and multi-female and semi closed to outsiders. Average groups can range in populations of 20-105 individuals. The Mahale Mountains support the highest population density of the “eastern race of chimpanzees in Tanzania.” (T. Nishida 25) 30% of the 2000 individuals live around Mahale.
A unit group of chimpanzees is prone to splitting into many subgroups or parties just like that of savanna baboons. Unlike the baboons however the only stable units are those comprised of others and their infants. The separate groups may act individually but follow a general pattern of movement seasonally north and south within their respective ranges. Although each part may seem to move randomly, the body of the whole “community” moves relatively as one. This drive is usually a result of ripening or abundant fruit. In one season almost all groups converged into a single square kilometer to feed on the abundance of Garnacia fruits. (Nishida 26)
Adult males tend to gather together in groups and groom. They show stronger social bonds than those between adult females or between adult males and females. (Kawanaka 1984) Male bonding is used primarily to facilitate the defense of their communal territory. Within the group there is a “linear form of dominance hierarchy.” (T Nishida 29) If a group has many males it can be difficult to observe the dominance between all individuals. In one study however, male chimpanzee groups fell into four categories of rank: alpha, high-ranking, middle-ranking and low-ranking individuals. Furthermore there is inherent reluctance in males to obey higher ranking members. Males may also avoid rivals unless accompanied by their own allies. Food sharing usually follows the basic line of hierarchy as does mating.
Male-female relationships differ greatly than those exhibited between males. If a female is not in estrous and a wide-ranging male arrives, he will sniff her genitals to glean her sexual state. Amazingly if the female is in estrus a male is more likely to groom her than if she was not. This is a clever tactic to win the hearts of receptive females.
Female-female relations among chimpanzees is a rather vague topic. Dominance is presumably based on age and tenure in a group. Sometimes females may form coalitions to unite against older adolescent males who display charge against them or against a male who bullies one of them. New (immigrant) females who give birth are quickly enmeshed with the community thanks to social bonding. Rarely, a new female will be rejected by the group and a female coalition could be constructed against her.
Hierarchy is clearly demonstrated during the feeding of meat which is a crucial and highly prized source of nutrients such as protein. Male animals starting with the most dominant snatch up the carcass and take the first picks then the meat goes to mothers and other subordinate males. If a juvenile is orphaned it is likely that it will not get any meat. The dominance asserted by male chimpanzees also is expressed in inherently violent acts. Jane Goodall’s observations of the chimpanzees of Gombe, depict a violent streak that chimps can share. At one point, the chimpanzee group she was studying broke off due the human interaction. Over the course of a few months one half of the split group systematically hunted and killed the members of the other group. War is obviously not a uniquely human trait.
Bonobos were often referred to as “pygmy chimps” due to their similar appearance and slightly smaller build. This is misleading since bonobos are a completely different species that show different behaviors, different reproductive patterns and even different autonomy. Bonobos live in a remote region south of the Zaire River in the Democratic Republic of the Congo. (Jurmain 147) They are to this day the least studied of the great apes. Since their recognition as a separate species in 1929, there has been many field observations of the species which has provided unique insight into their social structure. Like the chimpanzee, the bonobo social structure is fluid and in both species, the members of a large community do not travel and forage all together rather they form smaller bands which can change in composition. “The difference is that band of adult-male chimpanzees are quite common, but this is not true of bonobos.” (de Waal 180) In bonobos, the strongest attractions are between adult females and between the sexes. Bonds between males are relatively weak. “Hence the bonobo’s society differs fundamentally from that of the chimpanzee, with female bonobos taking a much more central positon.” (de Waal 180)
Males refrain from gathering and sharing food together as this causes tension however females show no such behaviors. Meat is a part of bonobo diet and although the males are the first to take the spoils they gingerly give portions to the females throughout the day. Sex plays a part in dining by forming cohesive bonds that form between members of hunting parties. Females unlike those of most other primates are almost continuously receptive and are willing to mate through much of their monthly cycles. This in turn leads to a new behavior amongst the animals that sex can be used as a medium for communication and bond forming much like social grooming.
In fact, “females not only mate with males but have sexual exchanges among themselves.” (de Waal 182) This sexual behavior fosters their own concept of “make love, not war.” These observations reveal a highly erotic lifestyle of bonobos. Bonding through sex may avoid competition among males and ease tensions with neighbors. During hunts and territorial displays, males must cooperate and sexual tensions may reduce effectiveness as a group. Thus the females of a group are divided among males in a stable arrangement. These pair bonds made through sex are not a sign of monogamy and males will accompany many different females forming bonds more cohesive than that of most other primates.
The bonobo is also well known for its correlations with many aspects of both behavior and anatomy with humans. Unlike chimpanzees, bonobos are much more comfortable standing upright. Their backs are much straighter and their heads sit more vertically on their spinal column. They are commonly bipedal and walk with a similar gait to that of humans. Also their sexual behavior mimics that of our own which is incredible and provides insight into early hominids.
Orangutans are the only species of Great Apes in the Genus Pongo and lives in a region that is substantially climatically and geographically different. Unlike the other great apes, the orangutan is a rainforest dwelling species adapted for life in the tree canopy. In the forests of Sumatra and Borneo there is a very different and lacking social structure. Orangutans spend most of their lives in solitude or with their mothers until they are grown. There are no definable characteristics that would suggest leadership as most social behavior especially grooming is rare.
The dominance within societies of orangutans is patriarchal and there is a hierarchy among males in a region. Yet it is also apparent that orangutans follow very different unsocial behaviors. Although most of these primates are solitary they nevertheless do communicate with other members of their species. Their calls are mainly to assert dominance over territory- crucial in a forest environment. Unlike other foresting apes such as the lesser apes (hylobatids) males and females are hardly ever seen together. The most common of semi-social units are “individual females with their dependent youngsters, lone adult and subadult males, and various small groupings of adolescents or singletons. Mother/young units and older youngsters sometimes join temporarily…” (Tuttle 255) Captive orangutans show very different approaches to social behavior and are much more socially interactive like the other great apes. However, in the wild it is questioned why orangutans become so solitary.
It is known that orangutan infants are very social and are dependent on their mothers for shelter and milk. Mothers take care of infants for its first two years. By the third year it learns to construct a nest and becomes increasingly playful and inquisitive around the same time. In the next few months the baby is slowly weaned from its mother’s milk. As a juvenile, orangutans between five and six years old become indifferent and inattentive to their mothers and although they stay within the same vicinity they start to engage in distinct activities by themselves. By the age of seven they are seldom groomed and lose their strong social bonds. This marks the beginning of their wandering lifestyle through the forests alone.
Socially, these primates lack group cohesion yet territorial instincts are very important to all adult individuals. The lack of social organization leads to a new need to not only maintain boundaries but to assert dominance and attract mates. To overcome these challenges proposed by distance, the orangutan is the third loudest primate in the world after howler monkeys and the Indri lemur. The orangutan’s calls vary like that of many primates and can travel up to two and a half kilometers through the densely packed forests of Borneo and Sumatra. The most studied vocalization of Pongo is the astounding “long call” which is only issued by adult males in their prime. It begins as a deep rumble with a vibrato (wavering notes) and increases to a deafening roar. Long calls are not common and in one study only one individual (old) male issued a call only twice a month. A different area of forest held a very powerful dominant adult male who issued calls three to four times a day. These calls also seem to hold display significance as over 20% of long calls are issued after males break branches and directly before they copulate. It is thought that the calls also “serve… to space adult males in the forest [and] attract sexually receptive females to the caller.” (Tuttle 22)
Mountain and low-land Gorillas have a unique social structure and a behavior that is beautifully suited to their environments. The mountain Gorillas live in an alpine/bamboo forest habitat local to the Virunga Volcanoes range in Africa. The separate peaks of Kivu, Mfumbiro, Birunga and Kirunga volcanoes are their primary homeland. The size of natural populous groups ranges from two to thirty individuals. An average group size is most probably six and seventeen animals. At one location where the animals aren’t hunted and there is an abundance of food the group size remained considerably higher.
In 1963, George B. Schaller became the first scientist to habituate mountain gorillas to the presence of humans. His research is invaluable and explains the majority of social group composure and traveling patterns. The composition of Gorilla groups are relatively constant and contain at least one silverbacked (dominant) adult male, one or more females and a variable number of youngsters. “More than one silverbacked male was found in five of the twenty-seven observable groups in the year 1959. In all five of these groups there were more than ten members. Females usually outnumber silverbacked and blackbacked males. In one location, Kabara, the average group “consisted of 1.7 silverbacks, 1.5 blackbacks, 6.2 juveniles and 4.6 infants.” (Schaller 104)
Studies on Ugandan Mountain Gorillas reveal that large groups sometimes divide into smaller subgroups with irregular compositions and then reunite later. Also these same groups contained wandering silverbacks that appeared to be lone males. These single male units were seen stumble into two of the stable groups and were accepted so long as the resident silver back male was dominant. When other silverbacks are present the hierarchy formed is linear.
Inter group encounters are not uncommon since gorilla territories zones tend overlap. Dominance can be physically asserted with charging displays, branch shaking, low calls and especially chest beating which can be heard from afar. Despite seeing charging and glaring warnings by dominant males during group encounters, Schaller concluded that gorillas are not territorial. “Usually members of different groups ignored one another and occasionally they mingled peacefully for several minutes before moving on.” (Tuttle 291) Still, different groups were not as tolerant of their neighbors. Like all animals, coexistence can be affected by abundance of resources and can change seasonally.
The dominant silverback male is the heart of a cohesive group while other less dominant individuals keep their respectful distance on the periphery. The silverback tends to lead the group through the movements of daily activity such as when to forage and travel, resting and nesting. The females in the group rely on his protection. When traveling as a group the silverback stays at the leading frontal position but if a threat is detected he drops to the rear of his group to protect them from behind. Gorillas solemnly directly attack the threat. When an attack is provokes the individual will lunge forward make brief contact and retreat.
Cohesiveness of the group is thought to be maintained not by social grooming or sex.
Schaller reported that, “Karbara gorillas rarely groomed and that grooming was never reciprocal.” (Tuttle 293) Instead grooming was solely used to remove their body of irritants they themselves could not reach- similar to the way a human can ask someone to scratch their back. Females are the only individuals inclined to grooming (only the infants). Blackbacked males never groom and females hardly ever groom each other. Youngsters like all the primates noted are playful. Play bouts observed are brief periods less than 15 minutes long and do not result in fights or arguments. Observations made by Dian Fossey yielded more information on behavior since she created more intimate bonds with her study group in the Parc De Volcans Mountains. She confirmed that gorillas lived their life in tranquility with an absence of inherent violence. So like the bonobos, gorillas expose the gentle nature of the great
apes.
Bibliography
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