differences in social hierarchies in wild vs captive chimp communities: cultural adaptation
DESCRIPTION
Analysis of the differences in social hierarchy and dominance between wild and captive chimpanzee communities as a result of cultural adaptation. Focuses on the lack of definitive dominance behaviours in captive chimpanzee populations, the tenuous nature of the "alpha male" designations, and greater apparent "rank" of females in captivity in relationship to the increasing significance of group composition and social awareness.TRANSCRIPT
Analysis of the differences in social hierarchy and dominance between wild and captive
chimpanzee communities as a result of cultural adaptation
Noelle Tankard
0000878101
Newbury Park High School
May 2007
(3,999 words)
Noelle Tankard Social hierarchy and dominance in chimpanzee communities
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Table of Contents
Abstract ..........................................................................................................................................................3
Introduction ....................................................................................................................................................4
Background ....................................................................................................................................................5
Chimpanzee social behaviors.....................................................................................................................5
Sexual differences ......................................................................................................................................6
Differences in wild and captive environments...........................................................................................7
Intelligence, learning, and culture..............................................................................................................8
Conventional wisdom: the alpha male ...........................................................................................................9
Case studies: Alphas in the wild ..................................................................................................................11
Gombe Stream..........................................................................................................................................11
Mahale Mountains....................................................................................................................................11
A different kind of leader.............................................................................................................................12
Captive Chimpanzee Populations ................................................................................................................13
Arnhem Zoo .............................................................................................................................................13
Los Angeles Zoo ......................................................................................................................................14
Other AZA Communities.........................................................................................................................16
Conclusion ...................................................................................................................................................17
Appendix 1: Chimpanzees mentioned .........................................................................................................19
Appendix 2: Notes on aggressive behavior..................................................................................................20
Works Cited .................................................................................................................................................21
Noelle Tankard Social hierarchy and dominance in chimpanzee communities
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Abstract
This paper explores the differences in the hierarchal structures of captive and
wild chimpanzee communities by focusing on the role, function, and identity of the
alpha male. Issues including the comparatively higher rank of females, the ambiguity
of individual leadership, and the lack of ritualized dominance behaviors are analyzed
as effects of such characteristics of captive environments as resource abundance,
security, and variable group composition.
The background information provided in the first section of the paper serves as
a context in which to understand the social structure and behavior of chimpanzees,
describes the applicable sexual differences, the fundamental differences in the captive
and wild environments, and briefly references the cultural learning capacities of
chimpanzees. This information helps to set up the hypothesis of cultural adaptation as
an explanation for the observed differences in dominance between captive and wild
communities. Appendices following the paper provide supplementary information.
The conventional model of chimpanzee dominance is directly explained by
reference to the variety of literature on the subject and indirectly described by the case
studies of Jane Goodall at Gombe Stream and Toshisada Nishida at Mahale Mountains
National Park.
The alternative model of leadership as demonstrated in captive environments
and the evidence to support the interpretation of cultural adaptation is presented in the
following portion. Several specific cases are examined, including Frans de Waal’s
study at the Arnhem Zoo and the contemporary chimpanzee populations of the various
American zoos, including the Los Angeles Zoo.
The conclusion, which finds cultural adaptation responsible for the observed
differences, presents a brief commentary on gender roles and function as well as a
fundamental challenge to the traditional understanding of dominance relationships as
well as the application of behavioral models based on wild behavior to captive
environments.
(290 words)
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Introduction
I volunteer for the Research Department of the Los Angeles Zoo. Although my involvement began
accidentally – striking up a conversation with a volunteer while visiting the zoo, attending a UCLA course in
ethology that began the same night, and subsequently becoming the youngest-ever member of the team – my prior
interest in paleoanthropology led me to seize the opportunity to observe the chimpanzees, whom I spent nearly two
years getting to know and respect as individuals before the study ended in August 2006. Last summer, I traveled to
Mahale National Park in Tanzania. Although many visitors spend days searching for a sight of the chimps, they
came down to the Nkungwe Camp each of the five days I stayed there. The first day, on a hike into the jungle, a
young male chimp, Darwin1, dragging a large branch behind him, rushed me in an aggressive display. One after
another I continued to see classic textbook behaviors of which I had only previously read: the alpha male led a hunt
and ate the catch (the chimps at the LA Zoo have been known to play with the corpse of a rat in their enclosure, but
are vegetarian2); the young and subservient greeted their elders with bows and gruff pant-hoots, males groomed
each other with hand-clasps and mothers, with a child following behind, carried their infants on their backs. Alofu,
perhaps following Darwin’s example, came to the camp and introduced himself as alpha in an inspiring display
involving the thick wooden poles that supported Tent 7. I was impressed not only by his percussion skills but by the
clear hierarchy.
The final key to my understanding came in October 2006 at the ChimpanZoo Conference3, where the
pattern of vague hierarchal arrangements, apparent lenience in the designated alphas, and the surprisingly high rank
of females as presented by keepers and observers from other captive environments, in tandem with discussion of
the problematic differences in environments led me to realize the broader significance of the differences I had
noted.
1 All chimpanzees mentioned by name are listed in Appendix 1 for reference.
2 Chimpanzees are omnivorous but can live healthily on a vegetarian diet. Although they eat meat in the wild, most captive
groups are never given meat to eat and as a result never learn to it or think of flesh as edible; this in itself is a cultural
adaptation to captive life. (Sclimenti 2006) 3 ChimpanZoo is an international coalition of zoos, sanctuaries, and other captive settings founded and funded by the Jane
Goodall Institute. Conferences meet yearly and attendance is open to the public. The theme and title of 2006 was “War of the
Worlds: Chimpanzee protection vs. chimpanzee exploitation.”
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Background
Chimpanzee social behaviors
Evaluating primates social hierarchies is quite difficult as identification of dominance behaviors is a highly
subjective process requiring evaluation of intent rather than result. (Discriminating between an attack and an
accident requires analysis of the initiator’s intent.) Ethology prefers empirical description over functional analysis
in initial observation, but as comparative studies require categorization, cautious delineation of even apparently
simple definitions is imperative. Dominance is formed by intraspecial social behaviors, which can generally be
classified as aggressive or affiliative.
“Aggression” popularly means “self-assertive or go-getting
behavior,” but ethologically denotes “behavior directed towards causing
physical injury to another individual,” according to Fedigan. To those
familiar with chimps, a problem is immediately apparent: non-contact
aggression, “bluff displays” in which chimps show off their strength and
attempt to intimidate others, constitute the vast majority of intracommunal
chimpanzee conflict. Only 1% of conflicts – 0.4% of conflicts between
males – result in physical clash (de Waal 1980, 87). The significant event
in dominance interactions is often the threat of a fight rather than the fight
itself. When a physical fight does occur serious injury is rare (males
restrain conflict to an apparent “unwritten” set of rules) and the response
of the remainder of the group to the fight and is just as important as the
outcome of the fight. (De Waal 1980).4
4 Please see Appendix 2 for additional information regarding the functions and definitions of aggressive behaviors.
Figure 1: “Figan brandishes a stick upon
seeing his reflection in a mirror,”
(Goodall 1971).
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Affiliative behaviors play an important role in hierarchal
formation. Physical domination is neither the sole nor determining factor
in dominance; sheer physical prowess is balanced by negotiation,
connections, alliances – essentially, politics (de Waal 1982). Alliances
are key; maintenance of a power position requires support and alphas are
frequently deposed not by a single challenger but a coalition. Building
relationships is time-consuming; the sharing of food and even mere
physical proximity are often as significant as overt action. Affiliation is a
broad generalization that includes grooming, playing, stationary contact,
and any sort of cooperation.
For the purpose of this analysis, I will use aggression synonymously with agonism5, considering all
behavior directed towards causing physical or psychological injury6 to another individual. Other behaviors, such as
mating and abnormalities7, enter this analysis extraneously.
Sexual differences
Chimpanzees are sexually dimorphic: males are larger, stronger, and though male and female hierarchies
are sometimes identified in parallel8, males are stereotypically dominant to females. Females hold responsibility for
infant care. As data from the LA Zoo reiterates, females spend a much larger portion of their time in affiliative
behavior, whereas male affiliation tends to be restricted to times of tension. Rank is dependent not only on an
individual’s own abilities and relationships, but on the rank of their siblings, and children (or vice versa); a high-
ranked female often passes her rank to her eldest daughter. In the wild, foreign males are seen as threatening but
5 In an attempt to avoid confusion between intentional and reactional aggression, the alternative term many alternative term
“agonism” , which excludes defense, and hunting, and interspecial conflicts, is used by many primatologists and ethologists to
isolate behaviors specific to social and dominance maneuverings. 6 I.e.: loss of status, rank, or confidence potentially but not necessarily as a result of physical injury.
7 E.g.: the ingestion or exploration of excrement, attempt by an adult male to nurse, an adult throwing a tantrum. Behaviors
designated “abnormal” (sometimes “undesirable”) in captive situations because they are symptomatic of larger problems. 8 In many communities, male and female hierarchies are delineated separately. The highest-ranking female is not dominant to
all other females, but holds the collective “female power” and often leading the females in fights against males and guiding
their support and affiliation with particular males.
Figure 2: Yeroen and Nikkie screaming
together, demonstrating their alliance (de
Waal 1980).
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females are welcome to emigrate9; their predilection for social affiliation is
indubitably helpful. Interestingly, sexual differentiation is less exaggerated:
Among monkeys living in conditions of relative safety and abundance,
males and females tend to be alike in functions, behaviors, and status.
Among monkeys living in more difficult conditions, males tend to be
specialized for leading the band, a function that requires high status,
and females for rearing the young; males and females are brought up in
different ways. (Russell 1972, 47.)
Safety and abundance are defining characteristics of captive chimpanzee life.
Interestingly, studies note that wild males are more gregarious than mothers,
whose attention is presumably focused on child-care (Wrangham 2000),
demonstrating the effect of resource abundance on social behavior.
Differences in wild and captive environments
The lack of hunger is the most profound difference in the lives of captive and wild chimps. Food never
concerns captive chimpanzees; nutrition is the constant obsession of wild chimps, who spend over half their time
foraging. Captive settings limit foraging (despite the best efforts of keepers and enrichment staff) and with
increased leisure time as a benefit, captive chimps have a much more concentrated social life (de Waal, 1986). The
lack of space also severely moderates the general fission-fusion10
social model of chimp communities (Sclimenti
2006).
Maturation rates differ significantly between wild and captive populations. Where Goodall’s observations
at Mahale set puberty at age 8 or 9, Jean and Zoe at the LA Zoo became pubescent at age 6. Goodall concluded that
males became socially mature at age 15; Jerrard at the LA Zoo became alpha male at the precocious age of 9. The
LA Zoo is not the only zoo or sanctuary to observe early maturation.11
Additionally, the medical attention available
to captive chimps greatly extends their life span (Conlee 2005).
9 Immigration between communities is a rare occurrence for females, generally exercised in early maturity or near the first
estrus, when their fertility is an obvious asset to a new community. 10
A social structure in which individuals come together occasionally but generally forage alone, common in primate species
with large habitats, often characterized by multiple smaller groups which break from the total community (Conlee 2005). 11
The accelerating rate of chimpanzee maturation in captivity may be linked to the increasing rate of modern human
maturation, which studies suggest is a result of improving nutrition and the increasing amount of hormones in our diet.
Figure 3: Yeroen and Luit groom
each other (de Waal 1980).
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Moreover, the problems that face chimpanzees in captivity are entirely different than those that face wild
chimps. Among captive populations physical danger is drastically limited: without access to other communities,
there is no potential for an escalation of violence and no need for males to physically
protect females and infants from external attacks; captivity’s lack of space and
vegetarian diet eliminate the hunt. The greatest stressor to captive chimps is the
introduction and reintroduction of strange individuals. Instead, the voluntary fission-
fusion of wild groups, the inconsistent group composition and the assimilation of
new individuals in captive settings12
, creates an unpredictable and presumably
stressful environment.
Intelligence, learning, and culture
Chimpanzees are capable of learning; through both observation and direct
training they share knowledge and techniques to a degree widely considered culture.
Jane Goodall’s radical discovery of chimpanzee tool use (1960) changed the understanding of chimpanzee
intelligence. Tool use and construction is now well documented in both
wild and captive environments and chimps have been seen to transmit
techniques between generations (Goodall 1971).
Apes are the indubitable masters of imitation (de Waal 2001).
Learning is more than imitation, and it occurs with less than expected
frequency:
The first … experiment seeding an expert tool user into a naïve
community found surprisingly little evidence of imitation.
Doubters soon began to ask: ‘Do apes ape?’ A raft of more
focused experiments ensued and [studies have shown]
‘emulation’, in which learning is focused on the outcomes of
what the model achieved rather than precisely how it was
done. The emerging picture is that apes do ape, but that
12
Sanctuaries deal with this to a larger extent than zoos, but both take in chimpanzees “retiring” from entertainment and
laboratory careers who not only have shorter life-expectancies than zoo/sanctuary-bred chimps, but whose poor health often
requires them to be pulled out from the group on a regular basis for medical care (Schultz 2006).
Figure 4: Flo fishes for
termites with a grass tool
(Goodall 1971).
Figure 5: Jonas watches Gorilla
extract insects from rotten wood (de
Waal 1980).
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imitation is just one of a ‘portfolio’ of varied social learning
processes, and perhaps most interestingly of all, it is applied
selectively. (Whiten 2005, 54.)
Experiments with captive chimps continue to raise our estimate of chimp
intelligence. Chimpanzees are capable of learning words, arranging them
in new formations and even inventing words13
(Goodall 1990). Chimps
are also able to lie and trick each other (Goodall 1990). Cultural
differences between wild populations include tools use, diet and greeting
customs.
Conventional wisdom: the alpha male
The alpha male is often the largest and most impressive member of a chimpanzee community, but his
strength and size are not determining factors in acquisition of rank. Maintenance of a power position often causes
the male to appear larger than he would otherwise due to the constant state of piloerection14
and increased
endocrine production. (Sapolsky 1993)
The considerable role of coalitions in the
power struggle combined with the prevalence of
bluff displays make it evident that much of the
dominance struggle is psychological. Formalized
dominance, rather than real dominance, is what
delineates the alpha’s identity. “Greeting is a …
ritualized confirmation [of] dominance,” (de Waal,
79) which, unlike grooming behavior that occurs
reciprocally (Goodall 1971), the lower-ranking
13
Washoe, a female chimpanzee who was raised in a human family and taught ASL, knows more than 300 words and taught
her adopted son Loulis many words, through direct coaching, and uses them not only with humans but other chimps. The first
time that she was exposed to a group of chimps who did not speak sign language she ran furiously back to her human
caregivers complaining about being left with the “dirty animals”. (Goodall 1990) 14
The physiological state of all body hair being pulled erect.
Figure 6: Nikkie as alpha (de Waal
1980).
Figure 7: Nikkie bows to Yeroen, who ignores him, while Luit
watches (de Waal 1980).
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always greets the higher-ranking (de Waal 1982). Greeting generally involves a “series of low, panting grunts” (de
Waal, 79) and though it may occur after a conflict it is not limited to reconciliation situations (de Waal 81).
Submissive males crouch before the dominant individual, who may acknowledge the greeting in a variety of ways
including vaulting over the submissive male’s back. The female greeting, an anogenital presentation is identical to
the sexual invitation (de Waal, 78).
Theoretically, the alpha male reserves all mating rights. When a female chimpanzee comes into estrus her
genital area swells for roughly ten days, during which time she is assiduously courted. Dominant males are
intolerant of other males mating – though many high ranking males will allow a close friend or ally to mate as a
“reward”– so other males attempt to lure swollen females away from the group to mate in secret (Goodall 1990).
The alpha male typically leads a hunt and “gets” the catch. He eats the meat or doles it out as he sees fit
(generally to females he wishes to court). In addition to presenting “prizes”, his interactions with the rest of the
group generally involve peace-keeping or “policing”:
“ [the] policing function… significantly contributes to maintaining stable resource
networks in the face of chronic perturbations that arise through conflict. … Policing not only
controls conflict, we find it significantly influences the structure of networks that constitute
essential social resources in gregarious primate societies [which play] a critical role in infant
survivorship, emergence and spread of cooperative behavior, social learning, and cultural
traditions.” (Flack, 426 in Nature)
Policing is incredibly important to the community. Other individuals, particularly in captivity may act in policing
functions15
but the alpha male is able to do so most effectively as a result of his authority.
15
At both Arnhem and the LA Zoo, past alphas were seen to perform policing functions, at times even more frequently than the
current alpha.
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Case studies: Alphas in the wild
Gombe Stream
The most dramatic power transition witnessed by Jane Goodall at
Gombe occurred in 1963. Mike rose from lowest ranking male to alpha,
thanks in large part to his display incorporating empty kerosene cans from the
camp into his displays: he dragged as many as six along the ground as he
ran.16
Once the former alpha, Goliath, accepted Mike’s dominance, they
developed a strong relationship (Goodall 1971). Mike was notably ambitious
and Goodall believes that even without the aid of human objects, he would
have achieved dominance due to his intelligence and courage.
Humphrey calmly succeeded the aging Mike, but was quickly
displaced by Figan (1973), whose intelligence and confidence as a youth
caused Goodall to predict his rise. Figan’s strong relationship with his older brother Faben17
helped him.
Humphrey, who had appeared quite nervous in front of Figan for some time, submitted after a single incident of
direct conflict. Figan maintained stability within the group, assiduously policed, and held a position of absolute
power for the first two years of his reign though he allowed Faben a large number of privileges, including mating
rights and meat.
Mahale Mountains
October 1965, Toshisada Nishida and a group of Japanese primatologists began an ongoing study at
Mahale Mountains National Park. The first stage aimed to “search for the social unit” (Nishida 1979, 92) and they
followed both the K and M groups. Over 7 years, the dominance hierarchy “remained stable”. Nishida noted the
tendency of young males to gain rank by forming a close association with an older male, a strategy that Goodall
referred to as “hero-following” (Goodall, 1990) and had conjectured was the key to identification of the alpha male
16
Once Mike learned to hurl the cans it became dangerous and efforts were made to insure that no cans were left within his
access, he attempted to use any other human object he could get his hands on, causing Goodall and her colleagues much
difficulty. (Goodall 1971) 17
Faben’s arm was crippled by polio and although still quite strong, he lacked the power to mount a campaign for power in his
own right. (Goodall 1971)
Figure 8: Mike bows to Goliath,
alpha (Goodall 1971).
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was by the frequency with which younger males chose to follow him. Kasonta was identified as alpha of the K-
group. He assumed leadership in scouting and chasing and the only male able to defeat a male from the M-group on
his own. Kasonta was intelligent and cautious, but not particularly “brave”: the most shy of any of the males and
took the longest to become habituated to human observers. (Nishida 1979)
A different kind of leader
Although researchers, keepers, and
observers begin with the assumption that there is
an individual who can be labeled the alpha due to
their rank and privileges and search to identify
that individual, this may be erroneous. Many
captive groups, due to their smaller size or family
bonds, may simply not contain a lead individual.
Nonetheless, the nature of dominance and its role
to group dynamics and the psychological well-
being of a chimpanzee community validates the
investigation of dominance and alpha identity.
The definition of alpha male roles and functions are, like all current chimpanzee behavioral models, based
on the behavior of wild chimpanzees. Studies at Mahale and Gombe have been used as a basis of comparison for
captive chimpanzees. Deviation, often symptomatic of a grave problem, is understandably worrisome. The
psychological health of captive chimps has been problematic and there have been significant efforts over the last 30
years, improving conditions and environments. The recent trend towards naturalism is a positive endeavor, the fact
remains that despite efforts, there are still, and always will be significant differences in the lives of captive and wild
chimpanzees. These differences are crucial and central to the behavior and personality of chimpanzees; creatures
with a high degree of social learning and culturalization.
Figure 9: Mama intervenes in a squabble between the adult Nikkie
and juvenile Fons by greeting and calming Nikkie and comforting
Fons (de Waal 1980).
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Furthermore, differences in the hierarchal behaviors of wild and captive chimps appear to directly
correspond to the environmental variations, as the following examples will illustrate.
Captive Chimpanzee Populations
Arnhem Zoo
Frans de Waal’s comprehensive analysis of chimpanzee hierarchy and dominance in 1979 at the Arnhem
Zoo established the significance of dominance in captive populations. The Arnhem community is one of the largest
in captivity, containing 25 individuals at the time of de Waal’s study and a very high number of males, along with a
large exhibit space and progressive design which makes the Arnhem community the closest approximation of wild
chimps in a captive setting and significantly different from other captive colonies.
A female named Mama had held the dominant
position in the Arnhem colony. When three mature males
were introduced, it was only through human interference18
that the trio was able to gain dominance over the rest of
the females. Yeroen’s subsequent dominance became
apparent in behavior and physiology: he was frequently
greeted submissively19
, never greeted anyone else, was
intolerant of other males mating, and physically striking.
Luit’s challenge was first displayed by mating
openly in front of Yeroen, and over the next two months,
Yeroen’s power eroded. During the transition, injuries were noted twice on the two males. Luit worked to isolate
Yeroen, who had dramatically increased the amount of time he spent in the company of adult females when Luit
began his challenge by interrupting his grooming bouts; Luit’s time spent in affiliative behavior with females
18
Mama and her closest ally, Gorilla, were removed from the group. When they retuned they had no support, as the other
females. This step was taken, de Waal explains, in response to the extremely high frequency and severity of violence in the
group following the introduction of the males. Yeroen’s aggression was far more restrained than Mama’s, whose fierce attacks
on the other chimps often caused injuries. Additionally, the keepers felt that as males are dominant in the wild the males would
inevitably achieve dominance and wished to protect the group from continuous violence until this occurred (de Waal, 1982). 19
At one point he received 90% of the pant-greetings and at no point less than 75%.
Figure 10: Nikkie bows to Luit, alpha (de Waal 1982).
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increased as he worked to gain their support. Yeroen had begun to throw “tantrums” to force the females to comfort
him, which stopped once he lost all support. The females did not support Luit until four months after he succeeded,
but the point at which they stopped supporting Yeroen was key to the dominance struggle. More important to Luit
than the female’s allegiance was his alliance with Nikkie. Nikkie had been subordinate even to many of the females
before Luit’s rise and afterwards, second only to Luit.
De Waal considered the dominance transition resolved when Yeroen was seen to greet Luit. Luit’s behavior
changed radically: previously, he had occasionally intervened in fights between females and children; now, the
frequency increased and he became a “loser-supporter”20
87% of the time, up from 35%. Both Nikkie and Luit
began to seek Yeroen’s friendship. Luit successfully prevented an alliance between Yeroen and Nikkie (which
would have allowed Nikkie to contend with him for power) for roughly three years, until Nikkie seized power in an
aggressive and violent takeover. Nikkie was feared, but not respected: although he received the majority of
greetings he was not groomed most often and he never became a loser-supporter. Yeroen continued to police,
preventing Nikkie from doing so, and regained as much respect and support from the females as he had received
during his time as alpha.
Los Angeles Zoo
In 1995 the LA Zoo’s Research Department organized a temporary study to observe the transition of the
chimp group into a new exhibit area. Three years later, unexpected pregnancies21
surprised the zoo and the study
was continued to monitor the infants, whose birth coincided with a power transition between the alpha male, Judeo,
and his son Jerrard. One of the infants was a victim of the struggle: Jerrard accidentally killed Toshi22
, and the other
infants were removed to be hand-raised. The study continued in order to follow the eventual reintroduction of the
20
“Looser supporter” is a term used by de Waal to refer to “an individual who intervenes in a conflict on the side of the party
who otherwise would have lost” (de Waal 1980), as opposed to a “winner-supporter”. 21
As a result of a failed vasectomy. 22
A third infant was placed with them: Zoe had been born to a lab chimp who was unable to raise or recognize her, and was
sent the LA Zoo. Zoe, born in Florida to a lab chimp who didn’t recognize her offspring, was brought to be raised with Jean
and Judeo. When the three reached three years of age in 2002, they were placed with Toto and Bonnie, the eldest male and
female. Bonnie suffered from diabetes and arthritis and needed to be separate from the energy of the main group and Toto, a
year older, kept her company and became particularly attached to the three young chimps; he played with them, comforted
them, and protected them from others (including those higher ranking than him) during the introductions that occurred during
the next three years.
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juveniles23
, which was finally completed in 2005, but the study once more stalled by new developments: the eldest
male died of heart failure and an increasing level of violence upset the precarious social balance as it became
apparent that Jerrard’s status was being challenged. Further issues, including the death of two more chimps and the
maturation of two young females complicated matters.
Group composition24
frequently changes for medical checkups or to avoid conflict. There are two
matriarchal lines: Pandora, and her offspring who have benefited from her high rank, and Bonnie’s descendents.
Jerrard’s precocious rise to power was in large part due to Pandora’s influence. Ripley benefited both from Pandora
and Jerrard’s power. Ripley is more adventurous but less belligerent than Glenn, who is roughly the same age.
Ripley spends much of his time away from the group, frequently playing with the juveniles. Shaun and Glenn,
Bonnie’s grandsons, had no such advantage; their mother, Nan, was frequently separated from the main group
during the last few years leaving them without her help. Shaun is two years older than Jerrard, slightly larger, and
known for his gentle temperament, though he often intervenes to maintain peace. Glenn has become the tallest,
leanest, and most aggressive of the males. He bullies the juveniles and frequently displays at the public. Judeo and
Jake can be disqualified from the dominance hierarchy due to their ages, respectively too old and too young. Judeo,
former alpha, continued to show many signs of being alpha: he performed a large portion of the peace-keeping
duties within the group before his death, was respected, and was followed in “hero worship” by Jake. Additionally,
he was a close ally to Jerrard, with whom he had developed a close relationship after being supplanted.
23
A third infant was placed with them: Zoe had been born to a lab chimp who was unable to raise or recognize her, and was
sent the LA Zoo. Zoe, born in Florida to a lab chimp who didn’t recognize her offspring, was brought to be raised with Jean
and Judeo. When the three reached three years of age in 2002, they were placed with Toto and Bonnie, the eldest male and
female. Bonnie suffered from diabetes and arthritis and needed to be separate from the energy of the main group and Toto, a
year older, kept her company and became particularly attached to the three young chimps; he played with them, comforted
them, and protected them from others (including those higher ranking than him) during the introductions that occurred during
the next three years. 24
The exhibit structure enables the chimps to split into as many as eleven separate groups. The chimps are generally kept in
two groups; “main group” refers to the larger.
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Pandora is generally referred to as the highest-ranking female, which
may be an understatement. She holds a position of great authority within the
group, is the main peace-keeper, and has a particularly interactive
relationship with the keepers, being known to intervene on the keeper’s
behalf at their request.25
It may be that some of her power derived from being
the alpha’s mother, nonetheless she is a significant figure in the group and
has never lost or decreased her influence.
Other AZA Communities
Marbles was without prior experience in a chimpanzee community
when he was transferred to the Sedgewick County Zoo and became the
default alpha. In his 20-year reign he never displayed many of the typical
behaviors: he did not stop aggressive displays or mating by other males and, in fact, showed little interest in mating
himself. Younger males began challenging him in 2000; Bahati dominated the group in 2001. Keepers at
Sedgewick note that dominance interactions are nominal. Pant-greetings are not present and the transition between
Marbles and Bahati was without conflict. In fact, there was more conflict following the death of the ranking female
and matriarch, Holly, in 2005, leading observers at Sedgewick to wonder if Holly had always outranked the
apparent alpha male. Holly, who had never shown extreme deference to Marbles or any male and had always
openly seized objects from them, both intervened in peace-keeping efforts and led the females in fights against the
males. Holly was quite close to Marbles until 2001; Bahati was able to take over only after Holly offered him
support and after her death, Moshi and Mahati challenged Bahati’s authority. Observers at Sedgewick say that there
is currently no clear alpha male or dominant individual. Although another female, Audra, attempted to take over
Holly’s peace-keeping role, she lacked authority, was severely injured during an intervention and backed off.
(Bailey 2006)
25
I was told a story by another researcher of a screwdriver falling into the chimp exhibit. Ripley, still young at the time, picked
it up and began to run about. Pandora, when offered an edible treat by the keepers, approached him, took the screwdriver, and
handed it to the keepers.
Figure 11: Pandora, highest-ranking
female and potential leader of the LA
Zoo group (Kaplan).
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The chimp community of the St. Louis Zoo originally had another “alpha by default”: Smoke, who was actively
dethroned by the next male to reach maturity, Hugo.
Sam, a wild-born male chimpanzee at the Sacramento Zoo, had grown up in contact with only two other
chimps. After their deaths he was introduced to another male, whose dominance he immediately accepted and never
challenged. When they fought, Sam always lead the reconciliation and seemed to act as peace-keeper between all
chimps in the group. (King 2006)
Conclusion
When I began this paper, I had no expectation of finding a succinct “answer” to the “problem” of the LA
Zoo’s hierarchy. I had hoped to determine the alpha at the LA Zoo, or to construct a captive dominance model –
both of which, it soon became apparent, were overly ambitious. Difficulties in obtaining and analyzing the data
from the Research Department, combined with my experiences in Mahale, impelled me to change direction. At the
ChimpanZoo Conference I became aware that “our problem” was common. The conference focused on the
difficulties of integrating psychologically-impaired chimps into social groups26
and behavioral differences from the
models were noted with worry; though several speakers noted that the aberrations of their chimps presented little
distress to their populations. When it was posited that simple “ignorance” was the key and that the idiosyncratic
chimps “simply didn’t know better” I began to wonder if what we were noticing were truly discrepancies or
whether a fundamental problem existed with the application of a dominance model to captive communities, i.e.
dominance defined by wild chimpanzees. At the time this idea was simply an inarticulate ramble in the margin of
my notes. After reviewing and analyzing both the original models and the captive situations, I am confident that
cultural adaptation has, and is, occurring.
In captivity, chimps neither hunt nor engage in skirmishes with foreign communities, resulting in the
decreased significance of male power reflected by the laxity of captive alpha males. Excellent diet and medical care
26
There are a large number of “professional” chimps due to the fact that the only chimps listed as endangered are those in
Africa; captive chimps are therefore not endangerd. While both professions require early retirement, neither involve any plans
or funds to retirement. As a highly cognitive and social species even the best of “working” situations leave the chimps
incapable of easy assimilation into a social group while the worst situations involve serious medical plight. (Conlee 2005)
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moderates the sexual dimorphism and differentiation, enabling females to hold greater authority and influence in
captive groups performing many of the alpha duties. Females more often demonstrate the skills significant to a
captive community, particularly affiliation with new and strange members. Frequent changes in group composition
necessitate the sharing of interventional authority.
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Appendix 1: Chimpanzees mentioned
Since Jane Goodall refused to comply with the ethological standard and refer to the chimps she studied at Gombe
by numbers, chimpanzees have been given names. To help clarify I have provided a list of all chimps mentioned in
this paper. Sibling relationships listed are maternal.
Arnhem Zoo
Luit: male, former alpha
Mama: Arnhem Zoo, oldest and highest ranking
female
Nikkie: Arnhem Zoo, male, current alpha
Yereon: Arnhem Zoo, high-ranking male,
former alpha
Gombe Stream National Park
Faben: male, older brother of Figan
Figan: male, alpha following Humphrey
Goliath: male, alpha preceding Mike
Humphrey: male, alpha following Mike
Mike: male, alpha following Goliath
LA Zoo
Bonnie: female, died 2006
Glenn: male, contender for rank, brother to
Shaun
Jake: male, born to Regina 1999
Jean: female, born to Gracie 1999
Jerrard: male, former/potential alpha
Pandora: highest ranked female, mother of
Jerrard, Gracie, and Ripley
Ripley: male, potential contender for rank,
brother to Jerrard
Shaun: male, potential contender for rank
Toshi: born to Yoshi in 1999 and killed by
Jerrard
Zoe: female, born in Florida
Mahale Mountains National Park
Alofu: M-group, male, current alpha
Darwin: M-group, male, adolescent
Kasonta: K-group, male, alpha
Kalunde: M-group, male, nicknamed “the
Kingmaker”
Sacramento Zoo
Joey: Sacramento Zoo, male
Sam: Sacramento Zoo, male
Sedgewick County Zoo
Bahati: male, former alpha
Gomez: male
Holly: female, died 2005
Mahati: male
Marbles: male, former alpha
Moshi: male
St. Louis Zoo
Hugo: male
Smoke: male
Washoe: at Central Washington University,
female, famous for ASL fluency
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Appendix 2: Notes on aggressive behavior
Aggression occurs for a variety of reasons in conflict situations. Fedigan cites Hamburg’s
identification of twelve main causational categories: protection of infants, competition for resources,
defense against predators, hunting other species, painful injury to an animal, long term changes in
dominance, daily dominance transactions, redirection downwards through the hierarchy, meeting an
unfamiliar animal, exploration of strange areas, and the crowding of strangers. The first four conflict
situations, while undeniably involving aggressive behaviors, have nothing to do with internal conflicts of
the sort necessary for evaluating dominance.
While the functions of aggressive interactions are clearly defined, the quantity and severity are
still not fully understood. Until 1972, primates were considered extremely vicious and dangerous. Jane
Goodall’s work at Gombe in Tanzania, among many other less prominent researchers, opened a new era
of primate ethology. The peaceful and intelligent aspects of chimpanzee behavior were observed and
emphasized. It was understood that the chimpanzee’s previous reputation of belligerence was built from
exaggerated and projected traveler’s tales and incomplete studies concerning out-of-context behavior in
extremely stressful situations.
As data continued to grow, however, and reports of isolated but continuing incidents of violence
came to light our understanding has become progressively less clear and more complex. Ironically, the
greatest and most sensational reports of violence stem from Goodall’s work at Gombe including the
“war” between the two groups in which males hunted, attacked, and killed members of the other group,
and the brief cannibalism of two females. While the violence at Gombe has continued to increase over
time, observations at the reserves at Budongo, Uganada and Mahale, Tanzania however, revealed
chimpanzee cultures far more peaceful. The major difference between the studies in the wild is the degree
of interaction with humans. At Gombe, in order to entice the chimpanzees to the camp, Goodall left out
bananas. The availability of food changed the Gombe chimpanzees’ social life as they began spending far
more time together in close proximity with a motive for competition. The effect of one such variable upon
the nature of their behavior is remarkable; chimpanzees in captivity, furthermore, spending 100% of their
time together, had adapted various other social conventions different from how they might behave in the
wild. Various observations in zoos helped reveal the great variability of chimpanzee social structures and
behaviors, which makes it even more important that each group be studied and observed individually.
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Works Cited
Bailey, Devin. (2006, October). Who’s the boss? A pet’s rise to power and the influence of his reign.
Speech presented at The ChimpanZoo Conference 2006, Los Angeles CA.
Conlee, Kathleen M. and Boysen, Sarah T. (2005). Chimpanzees in research: Past, present, and future. In
Deborah J. Salem and Andrew N. Rowan (Eds.), The State of Animals III: 2005. (119-133).
Humane Society Press.
de Waal, Frans B.M. and Bonnie, Kristin E. (2004). “Affiliation promotes the transmission of a social
custon: handclasp grooming among captive chimpanzees.” Primates. 47: 27-34.
de Waal, Frans B.M. (2001). The ape and the sushi master: Cultural reflections of a primatologists. New
York: Basic Books.
de Waal, Frans B.M. (1982). Chimpanzee politics: Power and sex among apes. Baltimore: Johns Hopkins
University Press.
Fedigan, Linda M. (1982). Primate paradigms. University of Chicago Press.
Flack, Jessica C., Girvan, Michelle, de Waal, Frans B.M., and Krakauer, David C. (2006). “Policing
stabilizes construction of social niches in primates.” Nature 439:426-429.
Goodall, Jane van Lawick- (1971). In the shadow of man. Boston: Houghton Mifflin Company
Goodall, Jane. (1990). Through a window: My thirty years with the chimpanzees of Gombe. Boston:
Mariner Books, Houghton Mifflin Company.
King, Laura. (2006, October). Girls just want to have power. Speech presented at The ChimpanZoo
Conference 2006, Los Angeles CA.
Kyles, Stephanie. (2006, October). Battle of the sexes: Aggression rates at the Sacramento Zoo. Speech
presented at The ChimpanZoo Conference 2006, Los Angeles CA.
Llyod, Alicia. (2006, October). Entertainer to Successful Patriarch: The Story of Mac the chimpanzee.
Speech presented at The ChimpanZoo Conference 2006, Los Angeles CA.
Nishida, Toshisada. (1979). “The Social Structure of Chimpanzees of the Mahale Mountains.” In D. R.
Hamsburg and E. R. McCown (Eds.), Great Ape Societies. (pp 73-81.) Menin Park, CA:
Benjamin/Cummings
Russell, C. and Russell, W.M.S. (1972). "Primate male Behavior and its Human Analogues" in Primates
on Primates. (pp 47-58.)
Sapolsky, Robert M. (1993). “The Physiology of dominance in stable versus unstable social hierarchies.”
In William A. Mason and Sally P. Mendoza (Eds.), Primate Social Conflict. (pp 171-204.)
Albany: State University of New York Press.
Sclimenti, Candace, Renzetti, Valentina, & Fox, Megan. (2006, September). Life Journeys: Toto, Bonnie,
and Minyak. Speech presented at The ChimpanZoo Conference 2006, Los Angeles CA.
Noelle Tankard Social hierarchy and dominance in chimpanzee communities
000878101
22
Schult, Billy. (2006, October). Aberrant Behavior in Captive Chimpanzees and Subsequent Problems for
Reintroduction Stemming from Human-Chimpanzee Interaction in Captive Settings. Speech
presented at The ChimpanZoo Conference 2006, Los Angeles CA.
Whiten, Andrew. (2005). “The second inheritance system of chimpanzees and humans.” Nature 437:52-
55.
Wrangham, Richard W. (2000). “Why are male chimpanzees more gregarious than mothers? A scramble
competition hypothesis.” In Peter M. Kappeler (Ed.), Primate males: Causes and consequences of
variation in group composition. (pp 248-258.)