2011

Sarah Ann Schaefer

ALL RIGHTS RESERVED

PERSONALITY, SUBJECTIVE WELL-BEING, AND VOCAL COMMUNICATION

IN CAPTIVE MALE WESTERN LOWLAND GORILLAS

by

SARAH ANN SCHAEFER

A Dissertation submitted to the

Graduate School-New Brunswick

Rutgers, The State University of New Jersey

in partial fulfillment of the requirements

for the degree of

Doctor of Philosophy

Graduate Program in Anthropology

written under the direction of

Dr. H. Dieter Steklis

and approved by

________________________

________________________

________________________

________________________

New Brunswick, New Jersey

May, 2011

ii

ABSTRACT OF THE DISSERTATION

Personality, Subjective Well-Being, and Vocal Communication in Captive Male Western

Lowland Gorillas

By SARAH ANN SCHAEFER

Dissertation Director:

Dr. H. Dieter Steklis

Although there have been studies on the meaning or function of gorilla vocalizations,

they have focused on correlations between calls and basic activity states. If gorilla

vocalizations, like human speech, provide information that is both semantic and

emotional, then we can expect to get a richer understanding of the meaning or function of

gorilla vocalizations by looking at the novel association between an individual’s

personality and its vocal profile (i.e. the types of calls predominantly given). Personality

drives and channels behavior and is therefore a higher level of analysis than basic activity

states. Four hypotheses are tested in this dissertation: 1) Personality predicts behavior in

captive gorillas; 2) Personality predicts vocal behavior (i.e. the vocal profile) in captive

gorillas; 3) Personality predicts subjective well-being in captive gorillas; 4) Subjective

well being predicts vocal behavior (i.e. the vocal profile) in captive gorillas. To test these

hypotheses, I used behavioral observation and personality and subjective well-being

questionnaires on eight male gorillas (five silverbacks; three blackbacks) at the Sedgwick

iii

County Zoo in Wichita, Kansas. The personality questionnaires used a modified top-

down approach, i.e. a modified five-factor model used in human personality studies. A

principle components analysis of the mean personality ratings revealed three components:

dominance; extraversion/agreeableness; conscientiousness. This is the first study to

document a conscientiousness factor in gorillas which was previously thought to exist

only in chimpanzees and humans. There were 16 significant correlations between

personality and behavior with an average r value of 0.76. Subjective well-being did not

predict behavior with the exception of contact aggression (r=0.71).

Extraversion/Agreeableness was significantly positively correlated with subjective well-

being and dominance was significantly positively correlated with ability to achieve goals.

Neither personality nor subjective well-being predicted vocal rate. Contrary to previous

reports, the gorillas in this study did not vocalize at a significantly different rate from

wild mountain gorillas. This is the first study to document individual vocal profiles of

gorillas, which have implications for captive management. Implications of the “singing”

and rhythmic multiple grunt vocalizations for the origins of music and language are

discussed.

iv

Dedication and Acknowledgements

This dissertation is dedicated with love to my parents, Dr. Donald and Anna

Marie Schaefer and to my eight gorilla friends: Shango, Barney, Tommy, Billy, Matt,

Virgil, Jabir, and Samson.

I am grateful to my graduate advisor, Dr. H. Dieter Steklis, for his support over

the past eight years and constructive criticisms and comments on early drafts. I would

like to thank Dr. Robin Fox, Dr. Lee Cronk, and Dr. Colin G. Beer for serving on my

committee and their helpful comments. Many thanks go to Dr. James King for sharing

his personality and subjective well-being questionnaires and for help with the statistical

analysis. Thank you to Netzin Gerald-Steklis for her support of this project. I am

grateful to Dr. Sandy Wilson, Mike Quick, and Mark C. Reed for permission to conduct

this research at the Sedgwick County Zoo and for their constant support of this project.

Many thanks to the gorilla keepers at the Sedgwick County Zoo for completing the

personality and subjective well-being questionnaires: Danielle Decker, Scott LaPlante,

Nathan Sexton, Ashley Suttles, Micala Teetzen, Julie Fritz, Amanda Jacquot, and Kelly

Rivera. I am grateful to the Sedgwick County Zoo, the Department of Anthropology and

the Center for Human Evolutionary Studies at Rutgers University for funding this

research.

v

Table of Contents

Page

ABSTRACT ii

DEDICATION AND ACKNOWLEDGEMENTS iv

TABLE OF CONTENTS v

LIST OF TABLES ix

LIST OF FIGURES x

CHAPTER 1: INTRODUCTION 1

1. Introduction 1

2. Limitations of Previous Studies 4

A. Gorilla Personality Studies 4

B. Vocal Communication in Gorillas 8

3. Contributions 12

4. Hypotheses and Predictions 14

CHAPTER 2: METHODS 18

1. Study Site 18

2. Housing 18

3. Subjects 18

A. Age Classes 18

B. Rearing History Definitions 19

4. Raters 20

5. Behavioral Observation Methods 21

6. Quantification of Behavioral Data 21

vi

7. Definition of Vocal Profile 22

8. Definition of Behavioral Categories for Table 13 22

9. Definition of Behavioral Categories for Table 14, 15, and 16 23

10. Vocal Recording Methods 25

11. Classification of Different Vocalizations 25

12. Rating Forms 26

A. Personality Questionnaire 26

B. Subjective Well-Being Questionnaire 32

CHAPTER 3: RESULTS 35

1. Personality and Subjective Well- Being Results 35

A. Interrater Agreement of Item Ratings 35

i. Personality 35

ii. Subjective Well-Being 35

B. Principal Components Analysis 38

i. Personality 38

ii. Subjective Well-Being 39

2. Hypotheses and Predictions Results 45

A. What is the Vocal Rate for Captive Gorillas? 47

3. Other Results that Provide Insight into the Meaning of Gorilla Calls 53

A. What is the Vocal Repertoire of Captive Gorillas? 53

B. Individual Gorillas’ Vocal Repertoire 55

C. Non-Syllabled and Syllabled Call Rates 63

D. Calls and Associated Age Classes and Contexts 64

vii

4. Summary of All Correlations between Personality and Behavior 65

5. Summary of All Correlations between Subjective Well-Being 67

and Behavior

6. Summary of All Correlations between Personality and Subjective 69

Well-Being

CHAPTER 4: DISCUSSION 70

1. Can Personality and Subjective Well-Being Inform our Understanding 70

of the Meaning of Gorilla Vocalizations?

2. Reliability and Validity of Personality and Subjective Well-Being 70

Measures

3. Principal Results 71

A. Personality Predicts Vocal Behavior (Vocal Profile) in Captive 71

Gorillas

B. Subjective Well-Being Does Not Predict Vocal Behavior 74

(Vocal Profile) in Captive Gorillas

C. Vocal Rates of Captive Gorillas 74

4. Limitations of this Study 75

5. Broader Implications of this Study 76

A. Personality and Vocal Communication in Gorillas 76

B. Is Vocal Repertoire Indicative of Subjective Well-Being 78

of Captive Gorillas?

C. Vocal Traditions (Culture) and Vocal Learning in Captive 79

Gorillas

D. The Origins of Music and Language in Gorilla 80

Vocalizations

6. Future Directions 84

viii

BIBLIOGRAPHY 86

CURRICULUM VITAE 96

ix

List of Tables

Page

Table 1 Sedgwick County Zoo Gorillas 20

Table 2 Interrater Reliabilities for Personality Traits 36

Table 3 Interrater and Internal Consistency Reliabilities for Subjective 37

Well-Being

Table 4 Factor Structure of Mean Adjectival Ratings 40

Table 5 Items Defining Each of the Three Gorilla Personality Factors 43

Table 6 T-Scores for the Three Gorilla Personality Factors 43

Table 7 Factor Profiles for the Sedgwick County Zoo Gorillas 44

Table 8 Correlations among Four Items on Subjective Well-Being Questionnaire 44

Table 9 Mean Vocal Rates of Sedgwick County Zoo Gorillas 49

Table 10 Mean Vocal Rates for Silverbacks in Gibeault Study 50

Table 11 Vocal Repertoire of Sedgwick County Zoo Gorillas and 54

Hypothesized Equivalent Call in Mountain Gorillas

Table 12 Non-Syllabled and Syllabled Vocalization Rates 63

Table 13 Calls and Associated Age Classes and Contexts 64

Table 14 Correlations between Personality Dimensions and Behaviors 65

Table 15 Correlations between Subjective Well-Being and Behaviors 67

Table 16 Correlations between Personality and Subjective Well-Being 69

x

List of Figures

Page

Figure 1 Mean Vocal Rates of Silverbacks in Captive and Wild Gorillas 51

Figure 2 Mean Vocal Rates of Silverbacks and Blackbacks at Sedgwick County 52

Zoo

Figure 3 Shango’s Vocal Repertoire 55

Figure 4 Barney’s Vocal Repertoire 56

Figure 5 Tommy’s Vocal Repertoire 57

Figure 6 Billy’s Vocal Repertoire 58

Figure 7 Matt’s Vocal Repertoire 59

Figure 8 Virgil’s Vocal Repertoire 60

Figure 9 Jabir’s Vocal Repertoire 61

Figure 10 Samson’s Vocal Repertoire 62

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Chapter 1

Introduction

Rendell and Whitehead (2001) suggest that scientists who study marine mammals

would benefit from approaching their studies more as ethnography than zoology. In this

way, each population of animals is thought of as having its own unique repertoire of

behaviors, or own unique culture (Brosnan, et al., 2009; Rothenberg, 2008; Rendell and

Whitehead, 2001). Primatologists would also benefit from this approach, especially since

the populations they are studying are often very small. This gives us the chance to look

at the behavior of individual gorillas more in-depth rather than viewing them solely as

members of a particular age/sex class. In this dissertation I will document the vocal

repertoire of eight male gorillas (five silverbacks; three blackbacks) that live in three

separate groups at the Sedgwick County Zoo in Wichita, Kansas. This dissertation is the

first attempt to address the question of whether personality can explain vocal profiles of

individual gorillas.

Although the importance of personality in the study of the great apes has been

understood since the 1960’s (Fossey, 1983; Goodall, 1971), it has rarely been studied

quantitatively through the use of questionnaires until the recent studies of chimpanzees

and orangutans by King and Figueredo (1997) and Weiss, et al. (2006). Because vocal

behavior is like any other behavioral category, such as playing or grooming, it has the

potential to be explained by personality dimensions. Vocal behavior, as a behavioral

category is often neglected in social behavior studies of the great apes (Mitani, 1996).

For gorillas, vocalizations are the most frequently occurring social behavior and they

account for seventy percent of all initiated behaviors (Steklis and Gerald-Steklis, 2004).

2

Like measures of aggression and affiliation, measures of an individual’s vocal behavior,

or vocal profile, should reflect an individual’s personality (Pederson et al., 2005). There

are no published studies demonstrating an association between personality dimensions

and vocal behavior in the non-human primates. However, this association has recently

been demonstrated for males of the collared flycatcher. Individual differences in the

choice for singing sites reflect individual differences in personality (Garamszegi, et al.,

2008).

If gorilla vocalizations, like human speech, provide information that is both

semantic and emotional (Seyfarth and Cheney, 2003; Marler, et al., 1992), we can expect

to get a richer understanding of the meaning or function of gorilla vocalizations by

looking at the novel association between an individual’s personality and its vocal profile

(i.e. the types of calls predominantly given) (Steklis, pers. comm.) The meaning and

function of gorilla vocalizations are inter-related as the meaning of particular

vocalizations is determined by the social function of the vocalization (Richman, 2000).

Thus, the meaning of a vocalization is its evolutionary adaptive function (Steklis, pers.

comm.).

If subjective well-being is a measure of an individual’s happiness then we can

expect to learn more about the meaning and/or function of gorilla vocalizations by

looking at any association between an individual’s subjective well-being and the rate of

which a particular call is given (King and Landau, 2003; Steklis, pers. comm.).

Subjective well-being in non-human animals used to be determined by the absence of

abnormal behaviors and the presence of normal, species-typical behaviors (King and

Landau, 2003). In humans, subjective well-being is defined by two correlated facets of

3

happiness that have been applied to non-human primates (King and Landau, 2003).

These two facets are a balance of positive and negative affect and a global evaluation of

one’s life (King and Landau, 2003). Additionally, a third factor, the amount of perceived

control over important events has been identified in human subjective well-being studies

and also applied to the non-human primates (King and Landau, 2003).

Humans have been shown to be able to reliably assess personality and subjective

well-being in chimpanzees and orangutans with high levels of reliability and validity

(Freeman and Gosling, 2010; Weiss, et al., 2006; King and Landau, 2003). This can be

explained by a phylogenetic generalization from human to ape of Ickes’ (1993) concept

of “empathic accuracy” or the ability to describe another person’s feelings (King and

Landau, 2003). Since it has been shown that humans can reliably assess the subjective

well-being of other humans (Parot and Diener, 1993) only a moderate inductive

generalization is required to accept that humans can reliably assess the subjective well-

being of apes (Weiss, et al., 2006; King and Landau, 2003). Furthermore, considering

that gorillas are one of our closest living relatives separated from us by only around eight

million years and with whom we share around 97% of our DNA it is the most

parsimonious approach to think that we share common feelings of happiness with them

(de Waal, 1996). King and Landau (2003) state that “…the absolute dichotomy between

understanding human and nonhuman conscious experience may not be as absolute as

Nagel (1974) implies, especially for nonhuman species closely related to humans.” (King

and Landau, 2003).

4

Limitations of Previous Studies

Gorilla Personality Studies

Personality can be described as “those characteristics of individuals that describe

and account for consistent patterns of feeling, thinking, and behaving” (Pervin and John,

1997). The term personality has often been used interchangeably with the term

temperament in the early studies on primate personality (Buirski, et al., 1978; Buirski, et

al., 1973); however, there is a difference. Temperament is now usually defined as “a

characteristic response style to novel stimuli or challenging situations that is largely

independent of immediate social or volitional influences” (Clarke and Boinski, 1995).

Personality refers to more specific social characteristics of the individual, for example,

the degree to which an animal is curious, playful, aggressive, dominant, etc. Thus,

personality traits are relatively easy to identify from repeated observations of group

living animals but more difficult to determine in nonsocial test situations in which the

single animal is exposed to some sort of novelty challenge. Reactivity, or temperament,

is therefore more difficult to determine in group-living situations (Clarke and Boinski,

1995).

While there have been numerous between species comparisons in personality,

there have been fewer within species comparisons of personality (Gosling, 2001). Early

attempts to describe personality in primates quantitatively, involved the emotions profile

index (EPI). This instrument was devised by Kellerman and Plutchik in 1968 for

evaluating personality in humans and was modified for non-human primate use by

Buirski and Plutchik (1973). The EPI is a 43-item forced choice test in which the choices

5

are scored in terms of eight basic emotion dimensions: trustful, dyscontrolled, timid,

depressed, distrustful, controlled, aggressive, and gregarious (Gold, 1993).

The five factor model is composed of five broad dimensions of personality that are

used to describe human personality; the factors are: extraversion; agreeableness;

openness; neuroticism; and conscientiousness (King and Figueredo, 1997). Although

there has been significant debate about the application of the five factor model in non-

human animals (Uher and Asendorpf, 2008; Gosling, 2001), it has several advantages.

These advantages are: it allows for between-species comparisons of personality through

the shared metric and it is consistent with evolutionary thinking while still being sensitive

to species-level differences in behavior (Weiss and Adams, 2008; Gosling and Graybeal,

2007). Critics have argued that the approach of King and colleagues is purely an etic, or

top-down, approach, but this is not correct. The approach of King and colleagues is a

modified top-down approach that takes into account species level differences while still

being consistent with evolutionary thinking (Weiss and Adams, 2008). In addition, King

and Weiss used exploratory factor analysis as opposed to confirmatory factor analysis so

that they did not impose the five factor model of humans onto the great apes (Weiss and

Adams, 2008). I also used exploratory factor analysis in this dissertation. The emic, or

bottom-up, approach of Uher is best for understanding personality trait expression in a

given species while the approach of King and Weiss is best for comparative personality

research on the great apes. Uher argues that with the top-down approach of King and

Weiss unique, important traits of a particular species that are ecologically valid will be

missed. Indeed, there is a difficult balance that must be met between the etic and emic

approaches.

6

Uher also raises concerns about the possibility of anthropomorphism and implicit

personality theory with a top-down approach. Implicit personality theory refers to the

idea that humans have a network of assumptions about the relationships between various

traits and behaviors. For example, individuals may assume that a happy person is also

friendly and that a quiet person is also timid and shy, but this is not necessarily the case.

However, Kwan, Gosling, and John (2008) found no evidence of anthropomorphic

projection in ratings of dog personality which provides support for the idea that humans

are not using implicit personality theory when judging the personality of nonhuman

animals. Uher also argues that in the great apes, the associations with manifest behaviors

are much stronger for her method of behavior-descriptive verbs (r=0.56) than for trait

adjectives(r=0.35). However, the results of my study contradict this claim (Uher and

Asendorpf, 2008). In my study which used trait adjectives the mean significant

correlation was (r=0.76; n=16).

There have been two quantitative studies on gorilla personality and they were

both done on captive gorillas (Gold, 1993; Kuhar, et al., 2006). One limitation with the

Kuhar et al. (2006) and Gold (1993) studies is that only twenty-five descriptive adjectives

were used and they did not attempt to replicate the five-factor model found in humans.

This means that they could not determine when the five factor model arose in our shared

evolutionary history with gorillas (King, pers.comm.). They did not include descriptive

adjectives that lead to a conscientiousness factor in humans and chimpanzees (Gosling,

2008). My study used fifty-four descriptive adjectives that were adapted from the

Goldberg (1990) adjective lists for the five factor model in humans by King and

colleagues (King and Figueredo, 1997) and that have been used in captive chimpanzee

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and orangutan personality studies (King and Figueredo, 1997; Weiss, et al., 2006). As

much as possible, an equal number of terms were selected from each of the five factors

used in the human study keeping in mind what factors seemed relevant to the particular

species being studied (King, pers. comm.). As a result, this study is the first to

demonstrate that a conscientiousness factor exists in extant gorillas (Gosling, 2008).

The Kuhar et al. (2006) study found only weak significant correlations between

some of the personality dimensions and behavior. This might be due to the fact that they

used an instrument designed to determine personality in macaques for gorillas (Freeman

and Gosling, 2010). It also might be due to the fact that theirs was a multi-institutional

study. The meaningfulness of the results of this approach are compromised because if

zoos have different gorillas and different raters the ratings are group relative (the group

means are clustered around the center of the rating scale) and therefore should not be

pooled together for analysis. In addition, behavior scores also have limitations for

between-settings comparisons as there are differences in group density, environmental

differences, and other factors. This study is the first to show that there are strong

significant correlations between certain personality dimensions and behavior, including

vocal behavior, for captive gorillas.

One limitation of the Gold (1993) study is that in preliminary data analyses few

relationships between personality and behavior were found (Kuhar, et al., 2006). This

remains an understudied question in the field of ape personality. Furthermore, neither the

Kuhar, et al. (2006) nor the Gold (1993) study addressed the concept of subjective well-

being in gorillas so this dissertation is the first to study that systematically and determine

whether subjective well-being is correlated with certain personality dimensions, as it is in

8

humans (Costa, P.T. and McCrae, R.R., 1980), chimpanzees (King and Landau, 2003)

and orangutans (Weiss, et al., 2006). Subjective well-being is positively significantly

correlated with extraversion in humans (McCrae and Costa, 1991; Costa and McCrae,

1980), chimpanzees (King and Landau, 2003), and orangutans (Weiss, et al., 2006) so

from an evolutionary standpoint we would expect it to be significantly correlated in

gorillas as well (King and Landau, 2003; de Waal, 1996). Additionally, if subjective

well-being measures the happiness of gorillas we could expect it to inform our

understanding of the meaning and /or function of gorilla vocalizations through the

association between subjective well-being and rates of specific calls. King found that

humans are able to reliably assess subjective well-being in chimpanzees and orangutans

with high levels of reliability and validity (Weiss, et al., 2006; King and Landau, 2003).

Additionally, subjective well-being was significantly positively correlated with

extraversion and dominance was significantly positively correlated with an ability to

achieve one’s goals in chimpanzees (King and Landau, 2003) and orangutans (Weiss, et

al., 2006)

Vocal Communication in Gorillas

Although there have been previous studies that addressed the meaning and function

of gorilla close calls (Schaller, 1963; Fossey, 1972; Harcourt et al., 1993; Mitani,

unpublished manuscript; Gibeault, unpublished manuscript), they have not been complete

or exhaustive. In the Schaller (1963) and Fossey (1972) studies the focus was on long

calls, or between-group calls, because the gorillas were not fully habituated. The

Harcourt et al. (1993) study did not look at individual vocal profiles of gorillas. Instead

the focus was on finding trends for specific age/sex classes, dominance ranks, and

9

relatedness. This dissertation documents variation in silverback and blackback vocal

profiles and how these differences relate to the individual gorillas’ personalities.

Harcourt and Stewart (2001) categorize gorilla close calls into two main types:

non-syllabled and syllabled. Non-syllabled vocalizations tend to be longer, i.e., longer

than one second, and do not have moments of silence that break up the sound. In other

words, the sound is continuous. Examples of non-syllabled vocalizations are singing and

rumbling. Syllabled vocalizations tend to be shorter and these short syllables are

separated by moments of silence. In other words, the sound is not continuous. Examples

of syllabled vocalizations include all the grunts (single, double, triple, inverted,

quadruple, and multiple) and the staccato-like chutter. Harcourt and Stewart (2001)

found that dominant individuals tend to give more syllabled vocalizations while

subordinate individuals tend to give more non-syllabled vocalizations. However, both

dominant and subordinate animals give both types of calls. They also found that kin tend

to exchange more calls than do non-kin. They found that close calls are given in two

main contexts: at times of potential separation, e.g., at the end of a rest period, and during

intense feeding, and at times of potential conflict, e.g., approaching one another during

feeding, when feeding intensively in close quarters or moving together as a group

(Harcourt, et al., 1993).

In both the Mitani and Gibeault unpublished manuscripts (Mitani, unpub. man.;

Gibeault, unpub. man.) correlations were determined between calls and basic activity

states such as feeding, resting, and moving. I argue that these provide limited insight into

the meaning or function of gorilla vocalizations especially when the same calls are given

in many different contexts such as is the case for gorilla “close calls”. (Seyfarth, et al.,

10

2010). By looking at personality we can understand the meaning and/or function of

gorilla vocalizations from a higher-level of analysis. Personality is not the same as

behavior. Personality “drives and channels” behavior and therefore slight changes or

differences in the higher-level phenomenon (personality) can have significant effects on

the lower-level one (behavior) (Capitanio, 2004). In other words, personality dimensions

can have a greater explanatory power for the meaning and/or function of gorilla

vocalizations than the usual vocalization/behavior correlation studies.

Similarly, measures of subjective well-being should inform our understanding of

the meaning and/or function of gorilla vocalizations because it is a measure of the

gorillas’ happiness. For example, we could ask why does one pair of brothers give many

chutter calls (a close- range agonistic, threat call) to the visitors (35% and 30% of their

vocal repertoire) while another pair of brothers rarely gives any chutter calls to the

visitors (<1% and 0% of their vocal repertoire)? Why does the pair that gives a lot of

chutters also give a lot of non-contact aggression to the visitors (1.83/hr; 0.88/hr) while

the other pair that rarely chutters also rarely gives any non-contact aggression to the zoo

visitors (0.20/hr; 0.08/hr)? Why does the pair of brothers that gives a lot of chutter calls

and non-contact aggression to the visitors score low on the conscientiousness personality

factor while the pair that does not give chutter calls or non-contact aggression to the

visitors score high on the conscientiousness personality factor? My study shows that

there is a significant negative relationship (r =-0.76) between the rate of chutter calls and

scores of the conscientiousness factor. In other words, gorillas scoring low on

conscientiousness (irritable, aggressive, unpredictable) give more chutter calls than males

who score high on conscientiousness (stable, cool, gentle). Male chimpanzees tend to

11

score very low on the conscientiousness factor (King, pers. comm.) and are very

intolerant and violent towards group outsiders and have even been described as

xenophobic (Diamond, 1992). So, aggression towards group outsiders (i.e. zoo visitors)

in the form of chutter calls and non-contact aggression can be understood as an

expression of low conscientiousness in a gorilla. This helps us to confirm the hypothesis

that one function of the chutter call is to serve as a close range threat and agonistic call

given to group outsiders.

It should be noted that it is impossible for us to determine precisely the meaning

of certain vocalizations as we cannot interview our subjects (Cheney and Seyfarth, 2007).

Meaning is imprecise. The philosopher W.V.O Quine called it the “radical

indeterminancy of meaning” (Cheney and Seyfarth, 2007; Quine, 1960). It is easier to

determine meaning when there is a discernable change in behavior in the recipient of the

call. With gorilla close calls, there is usually no change in the behavior of the recipient

other than giving an answering call in 60% of the cases (Harcourt and Stewart, 2001).

An essential first step in determining the meaning of primate vocalizations is to assess

any correspondence between a vocalization and its putative referent (Gouzoules and

Gouzoules, 2011). For example, is the caller dominant or subordinate to the recipient of

the call? Does the call occur during contact or non-contact aggression? Does the call

occur with both high and low quality foods? Does it occur when the food is divisible or

not divisible? Does it occur only with preferred foods or not? (Gouzoules and

Gouzoules, 2011). The idea that primate vocalizations either provide information to the

recipient or are given to manipulate the behavior of the recipient is a false dichotomy

(Seyfarth, et al., 2010). They do both. At the very least, we know that primate

12

vocalizations are individually distinctive and therefore provide information about the

identity of the caller (Cheney and Seyfarth, 2007). Playback experiments have been used

by some researchers as a means to get a better understanding of the meaning of primate

vocalizations, what an animal is thinking, and what an animal knows (Cheney and

Seyfarth, 2007; Gouzoules and Gouzoules, 2011; Snowdon, 2001; Slocombe and

Zuberbuhler, 2010). However, we should keep in mind that playback experiments, like

other captive experiments may be stressful to the animals, particularly since the animals

do not have a choice of whether to participate or not in the playback experiment (Ross,

2010). Other researchers have noted the possible ethical and logistical issues surrounding

playback experiments (Mitani, 1996; McGrew, 2010).

Although there are no published studies on captive gorilla vocal communication,

the general consensus within the field of primatology has been that captive gorillas do not

vocalize as much as wild gorillas. However, in an unpublished study of captive gorillas

the mean vocal rate for adult males was 22.22 vocalizations per hour, even higher than

the wild rate of 14 vocalizations per hour (Gibeault, unpublished manuscript; Harcourt et

al., 1993). If captive gorillas really were to vocalize significantly less than wild gorillas

this would be important to know because it could potentially speak to the gorillas’ sense

of well-being, health, and contentment (Fossey, 1983).

Contributions

This dissertation will contribute to the captive management and captive well-being

of gorillas. Gorilla keepers and the general public will have a better understanding of

what information and emotions the gorillas are communicating and in turn can be more

sensitive to their individual needs. The management of bachelor groups is an important

13

issue currently in the captive management of gorillas. Currently, there are twenty-eight

males that reside in all-male groups in ten zoos in North America and with eighty males

under the age of twelve (Wharton, 2001), this number is expected to increase in the near

future (Faust, et al., 2001; Stoinski, et al., 2004). This study will help to identify

particular males on the basis of personality who are more suited to living in all-male

groups (i.e. those males that score high on conscientiousness; high on

extraversion/agreeableness and low on dominance) (Gold, 1993). Identifying specific

gorillas that score low on subjective well-being tests can help gorilla keepers to better

meet the needs of these individuals.

In addition, this study will contribute to a better understanding of ape vocal behavior

and personality and the relationship between these two variables. With this dissertation,

we can now do a comparison of three of the four great apes (chimpanzees, gorillas, and

orangutans) and use these results to gain insight into when certain personality dimensions

arose in our hominid ancestors. Personality, like behavior, is subject to natural selection,

and therefore would have played a role in the evolution of hominins (King, et al., 1999).

Lastly, this study will contribute to a better understanding of the origins of language

in hominins. We know that the anatomy of the vocal apparatus in our earliest

australopithecine ancestors was similar to that of modern day great apes (Tattersall,

2002). In addition, early hominin social structure was probably more gorilla-like (i.e.

cohesive, one to several male polygynous groups) than chimpanzee-like (frugivore,

fission-fusion type) (Watts, 1996; Boyd and Silk, 2008). Therefore, we can use insights

from gorilla communication as a model for how our earliest ancestors communicated.

14

Hypotheses and Predictions

Hypothesis 1: Personality predicts behavior in captive gorillas.

Personality has been shown to accurately predict behavior in humans (Nettle, 2006;

Meyers, et al., 2001) and chimpanzees (Pederson, et al., 2005) as demonstrated through

strong significant correlations between personality and behavior. However, in the only

study on gorillas the relationship between behavior and personality was weak (Kuhar, et

al., 2006).

Prediction 1

Dominance will be positively correlated with aggressive behaviors (DISPLACE; NCA;

CA; NCAVIS; AGON) as has been shown in chimpanzees (Pederson, et al., 2005)

Prediction 2

Extraversion will be positively correlated with measures of affiliation (PLAY; GROOM;

TOUCH; SEX; APPROACH (ALL); APP ME; APP VIS; APP GOR; AFFIL) (Pederson,

et al., 2005)

Hypothesis 2: Personality predicts vocal behavior (i.e. the vocal profile) in captive

gorillas.

Studies demonstrating the relationship between personality and behavior are rare

although this relationship was recently demonstrated for birds (Garamszegi, et al., 2008).

If gorilla vocalizations are like human speech then we can predict that gorilla

vocalizations will send information about the intentions, motivations, and emotions of the

gorillas (Steklis, pers. comm.).

15

Prediction 1

There will be a positive relationship between dominance and vocal rate (Harcourt and

Stewart, 2001).

Prediction 2

There will be a positive relationship between dominance and syllabled calls(Harcourt and

Stewart, 2001).

Prediction 3

There will be a negative relationship between dominance and non-syllabled calls

(Harcourt and Stewart, 2001).

Prediction 4

There will be a positive relationship between dominance and double grunts (Harcourt and

Stewart, 2001).

Hypothesis 3: Personality predicts subjective well-being in captive gorillas.

It has been demonstrated that personality predicts subjective well-being in humans

(McCrae and Costa, 1991; Costa and McCrae, 1980), chimpanzees (King and Landau,

2003), and orangutans Weiss, et al., 2006).

Prediction 1

There will be a positive relationship between extraversion and subjective well-being

(King and Landau, 2003; Weiss, et al., 2006).

16

Prediction 2

There will be a positive relationship between dominance and an ability to achieve goals

(King and Landau, 2003; Weiss, et al., 2006).

Hypothesis 4: Subjective well-being explains vocal behavior (i.e. the vocal profile) in

captive gorillas.

With a few exceptions, subjective well-being did not explain behavior in chimpanzees

(King and Landau, 2003).

Prediction 1

Captive gorillas will have a lower vocal rate than wild gorillas.

Although there have been no published studies on captive gorilla vocal rates,

Gibeault (unpublished manuscript) found that captive gorillas did not vocalize

significantly less than wild gorillas. However, the general impression in the academic

and zoo communities has been that captive gorillas do vocalize less than wild gorillas for

reasons unknown but hypothesized that the increased stress due to captivity results in less

vocalizations. In fact, gorillas of the tourist groups in Rwanda were found to give less

“belch vocalizations”, or contentment vocalizations than the groups of gorillas visited

only by researchers (Steklis and Gerald-Steklis, 2004). The most frequently given

vocalization in wild gorillas, the double grunt, was hypothesized to be indicative of the

gorillas’ contentment (Fossey, 1983); therefore if captive gorillas are more stressed than

wild gorillas it should follow that there will give fewer contentment vocalizations such as

the double grunt if subjective well-being correlates with the rate of double grunts.

17

Prediction 2

There will be a positive relationship between subjective well-being and vocal rate

(Fossey, 1983).

Prediction 3

There will be a positive relationship between subjective well-being and contentment calls

(double grunt; rumble) (Fossey, 1983).

18

Chapter 2

Methods

Study Site

This research was conducted at the Downing Gorilla Forest exhibit at the

Sedgwick County Zoo in Wichita, Kansas from August 2007 until March 2008.

Housing:

The Downing Gorilla Forest at the Sedgwick County Zoo consists of four housing

possibilities for the three groups of gorillas: the outdoor exhibit (31,000 square feet) that

is open to visitors; the indoor public dayroom (2,200 square feet; 21 feet tall) that is open

to visitors; the non-public dayroom (2,400 square feet; 21 feet tall) that is not open to

visitors; and the eight bedrooms (each bedroom 12 feet long; 9 feet wide; 12 feet tall) that

are not open to visitors. The three groups are rotated between all four enclosures during

warm months, and between the three indoor exhibits during cold months.

Subjects

Age Classes:

I used the age/class definitions provided by Harcourt and Stewart (2007).

Gorillas between the ages of eight years old and twelve years old were classified as

blackbacks (Harcourt and Stewart, 2007) and gorillas thirteen years old and older were

classified as silverbacks (Harcourt and Stewart, 2007). There were five silverbacks and

three blackbacks in this study which resided in three separate groups. The first group

consisted of two silverbacks, Shango and Barney. The second group consisted of two

19

silverbacks, Tommy and Billy. The third group consisted of one silverback, Matt and

three blackbacks, Virgil, Jabir, and Samson.

Subjects were eight western lowland gorillas (Gorilla gorilla gorilla) housed in

three separate groups. The Shango/Barney group contained two silverbacks, Shango,

aged 18 years and Barney aged 13 years. The Tommy/Billy group contained two

silverbacks, Tommy, aged 18 years and Billy aged 16 years. Matt’s group contained one

silverback, Matt, aged 14 years, and three blackbacks, Virgil aged 8 years, Jabir aged 8

years, and Samson aged 8 years. See Table 1 on page 20 for more details.

Rearing History Definitions:

Animals that were with their mothers continuously or separated from their

mothers for fewer than six months within the first three years were considered parent

reared. Individuals that were separated from their mothers for more than six months

within the first three years of life were considered hand reared (Stoinski et al., 2004).

There were four parent reared animals (Shango, Barney, Jabir, and Samson) and four

hand reared gorillas (Tommy, Billy, Matt, and Virgil) in this study.

Shango and Barney are full brothers and were parent-reared. Tommy and Billy

are full brothers and were hand-reared. Matt is not related to any other gorilla at the

Sedgwick County Zoo and was hand-reared. Virgil and Jabir are paternal half-brothers

and their mothers are full-siblings. Virgil was hand reared and Jabir was parent-reared.

Samson’s mother is Virgil’s and Jabir’s maternal grandmother. Samson was parent-

reared.

20

Table 1. Sedgwick County Zoo gorillas

Group Studbook# Name Sex Age DOB BT RH

SH/BA 1123 Shango M SB 3/11/89 C P

SH/BA 1309 Barney(Ike-Ozo) M SB 10/12/93 C P

TO/BI 1039 Tommy M SB 9/2/88 C H

TO/BI 1148 Billy M SB 10/17/90 C H

Matt’s

Grp

1304 Matt(Matumaini) M SB 6/11/93 C H

Matt’s

Grp

1544 Virgil(Amiri) M BB 3/21/99 C H

Matt’s

Grp

1498 Jabir M BB 11/30/98 C P

Matt’s

Grp

1497 Samson M BB 11/25/98 C P

SB=silverback; BB=blackback; BT=Birth Type; C=Captive;RH=rearing History;

P=Parent-Reared; H=Hand-Reared

Raters:

There were a total of nine raters for the eight gorillas. Each rater filled out a

personality questionnaire and a subjective well-being questionnaire for each of the eight

gorillas. One rater was the author, while the other eight raters were gorilla zookeepers

who knew the gorillas for a period ranging from 2 months to 3.8 years (2 months; 3

months; 2 yrs; 3 yrs; 3.5 yrs; 3.7 yrs; 3.8 yrs; 3.8 yrs). I knew the gorillas for a period of

7.5 months.

21

Behavioral Observation Methods:

Data collection occurred from August of 2007 until March of 2008. The majority

of focal data occurred while the gorillas were in the “public dayroom” of the Downing

Gorilla Forest exhibit. This is because the public dayroom is the only enclosure that does

not have any “blindspots”. I could view every space of the enclosure without having to

move from my station (around the midway point along the wire mesh side of the

enclosure) and therefore could keep track of all the gorillas simultaneously. Visitors are

able to view the gorillas from behind glass on one side of the enclosure and I was

stationed behind the wire mesh side of the “public dayroom”, directly across from the

glass side of the enclosure. So the gorillas were in an oval-shaped enclosure of 2,200

square feet with the visitors on one side behind glass and I on the other side behind wire

mesh, directly across from the visitors. During the habituation period data were collected

primarily while the gorillas were in the “non-public dayroom” where the gorillas are off-

exhibit and also when the gorillas were in their bedrooms which are also off-exhibit.

Behavioral observations consisted of 50-minute focal animal follows on all eight

gorillas (Altmann, 1974). There were a total of 199 50-minute focal animal follows and

at least an additional 400 ad lib hours.

Quantification of Behavioral Data:

I calculated rates of behavior by dividing the total number of times a gorilla

executed a particular behavior during their focal observations by the total number of

hours I observed that particular gorilla. These rates were used in the correlations between

behaviors and personality dimensions and between behaviors and subjective well-being.

22

Definition of Vocal Profile:

1) overall mean vocal rate

2) rate of non-syllabled (NS) calls

3) rate of syllabled (S) calls

4) rate of agonistic calls (chutter (CHUT))

5) rate of contentment calls (double grunt (DG); rumble (RUM)

Definition of Behavioral Categories for Table 13:

1) RES= REST= sitting, lying down, sleeping, not engaged in any of the other

behavioral categories listed.

2) FEE=FEED= to take in solid foods into mouth, chew, and swallow.

3) MOV=MOVE= any movement not associated with foraging.

4) PLAY= non-aggressive interaction with both partners participating actively with

such behaviors as wrestling, chasing, and pushing.

5) SEX= instances of mounting with thrusting and intromission.

6) AGON/SPACING= AGONISTIC/SPACING BEHAVIOR

7) APP=APPROACH= to move towards another animal in a non-threatening manner

to within 2 meters.

8) ALARM= reaction to a strange or unusual noise from an extraneous source such

as a plane.

9) NCA=NON-CONTACT AGGRESSION= charge, chase, “follow or stalk”,

display.

23

Definition of Behavioral Categories for Table 14, 15, and 16:

1) DISPLACE= one animal moves to within 1 meter of original spot of another

gorilla and displaced gorilla moves at least 1 meter away from its original spot.

2) NCA=NON-CONTACT AGGRESSION= charge, chase, “follow or stalk”,

display.

3) CA=CONTACT AGGRESSION= (hit, kick)

4) NCAVIS=NON-CONTACT AGGRESSION TO VISITORS

5) PLAY= non-aggressive interaction with both partners participating actively with

such behaviors as wrestling, chasing, and pushing.

6) GROOM (ALOGROOM) = to pick at, scratch, or remove debris from fur of

others.

7) TOUCH= a gentle placing of the hand on another’s head, shoulder or back.

8) SEX= instances of mounting with thrusting and intromission.

9) APPROACH (ALL)= to move towards another animal in a non-threatening

manner to within 2 meters.

10) APPME= APPROACH AUTHOR= see above

11) APPVIS= APPROACH VISITORS= see above

12) APPGOR= APPROACH GORILLAS= see above

13) SOLOPLAY= play behaviors done by a gorilla by itself.

14) VOCRATE= the overall mean rate of vocalizations per hour.

15) NSVOCRATE= the overall mean rate of non-syllabled vocalizations per hour.

24

16) SVOCRATE= the overall mean rate of syllabled vocalizations per hour.

17) CHUT= a harsh, staccato, syllabled call given at a close-range, mild threat to

group intruders and to females from silverbacks.

18) PURR= a grunt of one beat of varying length by individual gorilla.

19) PIG G= a harsh, mild threat vocalization given usually in a feeding context.

20) DG= a grunt of two beats, with the second syllable usually longer than the first

syllable.

21) RUM= a non-syllabled vocalization given during feeding.

22) HOOT= given within a succeeding chestbeat serves as a “lost call” when

separated from other group members; given with a succeeding chestbeat serves as

a display to non-group members.

23) SING=a non-syllabled vocalization given just prior to feeding.

24) LAUGH=breathy vocalization given usually given during play.

25) AGON=displace, non-contact aggression, contact aggression, non-contact

aggression to visitors.

26) AFFIL=play, groom, touch, sex, approach with other gorillas.

27) PUBLICORIEN(NCA & APP)= non-contact aggression to visitors and

approaching visitors.

25

Vocal Recording Methods:

Vocalizations of the gorillas were recorded using a Marantz Solid State digital

recorder, model PMD670, and a Sennheiser directional microphone. All recordings were

taken when the gorillas were in one of the three possible indoor enclosures: the bedrooms

(non-public); the non-public dayroom; and the public dayroom. Recordings were not

taken when the gorillas were in the outdoor enclosure because the distance was too great

and the waterfall would have degraded the quality of the recordings.

Classification of Different Vocalizations:

I used my previous training experiences at the Karisoke Research Center in

Rwanda and the Gorilla Foundation in Woodside, California in learning different types of

gorilla vocalizations to aid in the classification of gorilla vocalizations at this site. Most

of the vocalizations heard at this site had already been heard by the author before, with

the exception of the multiple grunt and the quadruple grunt which has not been

documented in wild gorillas but has been documented in another captive gorilla study

(Gibeault, unpublished manuscript). I classified different calls based on how they

sounded to the naked ear and used a contextual and functional approach to aid in

differentiating calls. In other words, an emic approach from the perspective of the

gorillas was used rather than an etic approach, from the perspective of the scientist and

the sonagram (Weiss, et al., 2006). It is important for researchers to keep in mind that

what constitutes a structurally discrete call to the researcher may be different from how it

is perceived by the animal (Gouzoules and Gouzoules, 2011). Animals may not

“partition the acoustic space” in the same way as the researchers (Evans, 1997).

26

Rating Forms:

Personality Questionnaire:

The Gorilla Personality Trait Assessment form was devised by Dr. James King

and is very similar to the questionnaires he and his associates used for their chimpanzee

(King and Figueredo, 1997) and orangutan (Weiss, et al., 2006) personality studies. The

raters were given the following instructions for filling out the forms:

Gorilla personality assessments can be made with this questionnaire by assigning

a numerical score for all of the personality traits listed on the following pages. Make

your judgments on the basis of your own understanding of the trait guided by the short

clarifying definition following each trait. The gorilla’s own behaviors and interactions

with other gorillas should be the basis for your numerical ratings. Use your own

subjective judgment of typical gorilla behavior to decide if the gorilla you are scoring is

above, below, or average for a trait. The following seven point scale should be used to

make your ratings:

1. Displays either total absence or negligible amounts of the trait.

2. Displays small amounts of the trait on infrequent occasions.

3. Displays somewhat less than average amounts of the trait.

4. Displays about average amounts of the trait.

5. Displays somewhat greater than average amounts of the trait.

6. Displays considerable amounts of the trait on frequent occasions.

7. Displays extremely large amounts of the trait.

27

Additional instructions given were the following:

Please give a rating for each trait even if your judgment seems to be based on a

purely subjective impression of the gorilla and you are somewhat unsure about it.

Indicate your rating by placing a cross in the box underneath the chosen number.

Finally, do not discuss your rating of any particular gorilla with anyone else. As

explained in the handout accompanying this questionnaire, this restriction is necessary in

order to obtain valid reliability coefficients for the traits.

1. Fearful: subject reacts excessively to real or imagined threats by displaying

behaviors such as screaming, grimacing, running away or other signs of anxiety or

distress.

2. Dominant: Subject is able to displace, threaten, or take food from other gorillas.

Or subject may express high status by decisively intervening in social

interactions.

3. Persistent: Subject tends to continue in a course of action, task, or strategy for a

long time or continues despite opposition from other gorillas.

4. Cautious: Subject often seems attentive to possible harm or danger from its

actions. Subject avoids risky behaviors.

5. Stable: Subject reacts to its environment including the behavior of other gorillas

in a calm, equable way. Subject is not easily upset by the behaviors of other

gorillas.

6. Autistic: Subject often displays repeated, continuous, and stereotyped behaviors

such as rocking or self-clasping.

28

7. Curious: Subject has a desire to see or know about objects, devices, or other

gorillas. This includes a desire to know about the affairs of other gorillas that do

not directly concern the subject.

8. Thoughtless: Subject often behaves in a way that seems imprudent or forgetful.

9. Stingy/Greedy: Subject is excessively desirous or covetous of food, favored

locations, or other resources in the enclosure. Subject is unwilling to share these

resources with others.

10. Jealous: Subject is often troubled by others who are in a desirable or

advantageous situation such as having food, a choice location, or access to social

groups. Subject may attempt to disrupt activities of advantaged gorillas.

11. Individualistic: Subject’s behavior stands out compared with that of the other

individuals in the group. This does not mean that it does not fit or is incompatible

with the group.

12. Reckless: Subject is rash or unconcerned about the consequences of its behaviors.

13. Sociable: Subject seeks and enjoys the company of other gorillas and engages in

amicable, affable, interactions with them.

14. Distractable: Subject is easily distracted and has a short attention span.

15. Timid: Subject lacks self confidence, is easily alarmed and is hesitant to venture

into new social or non-social situations.

16. Sympathetic: Subject seems to be considerate and kind towards others as if

sharing their feelings or trying to provide reassurance.

17. Playful: Subject is eager to engage in lively, vigorous, sportive, or acrobatic

behaviors with or without other gorillas.

29

18. Solitary: Subject prefers to spend considerable time alone not seeking or avoiding

contact with other gorillas.

19. Vulnerable: Subject is prone to be physically or emotionally hurt as a result of

dominance displays, highly assertive behavior, aggression, or attack by another

gorilla.

20. Innovative: Subject engages in new of different behaviors that may involve the

use of objects or materials or ways of interacting with others.

21. Active: Subject spends little time idle and seems motivated to spend considerable

time either moving around or engaging in some overt, energetic behavior.

22. Helpful: Subject is willing to assist, accommodate, or cooperate with other

gorillas.

23. Bullying: Subject is overbearing and intimidating towards younger or lower

ranking gorillas.

24. Aggressive: Subject often initiates fights or other menacing and agonistic

encounters with other gorillas

25. Manipulative: Subject is adept at forming social relationships for its own

advantage, especially using alliances and friendships to increase its social

standing. Gorilla seems able and willing to use others.

26. Gentle: Subject responds to others in an easy-going, kind, and considerate

manner. Subject is not rough or threatening.

27. Affectionate: Subject seems to have a warm attachment or closeness with other

gorillas. This may entail frequently grooming, touching, embracing, or lying next

to others.

30

28. Excitable: Subject is easily aroused to an emotional state. Subject becomes

highly aroused by situations that would cause less arousal in most gorillas.

29. Impulsive: Subject often displays some spontaneous or sudden behavior that

could not have been anticipated. There often seems to be some emotional reason

behind the sudden behavior.

30. Inquisitive: Subject seems drawn to new situations, objects, or animals. Subject

behaves as if it wishes to learn more about other gorillas, objects, or persons

within its view.

31. Submissive: Subject often gives in or yields to another gorilla. Subject acts as if it

is subordinate or of lower rank than other gorillas.

32. Cool: Subject seems unaffected by emotions and is usually undisturbed, assured,

and calm.

33. Dependent/Follower: Subject often relies on other gorillas for leadership,

reassurance, touching, embracing and other forms of social support.

34. Irritable: Subject often seems in a bad mood or is impatient and easily provoked

to anger, exasperation, and consequent agonistic behavior.

35. Unperceptive: Subject is slow to respond or understand moods, dispositions, or

behaviors of others.

36. Predictable: Subject’s behavior is consistent and steady over extended periods of

time. Subject does little that is unexpected or deviates from its usual behavioral

routine.

37. Decisive: Subject is deliberate, determined, and purposeful in its activities.

31

38. Depressed: Subject does not seek out social interactions with others and often

fails to respond to social interactions of other gorillas. Subject often appears

isolated, withdrawn, sullen, brooding, and has reduced activity.

39. Conventional: Subject seems to lack spontaneity or originality. Subject behaves

in a consistent manner from day to day and stays well within the social rules of

the group.

40. Sensitive: Subject is able to understand or read the mood, disposition, feelings, or

intentions of other gorillas often on the basis of subtle, minimal cues.

41. Defiant: Subject is assertive or contentious in a way inconsistent with the usual

dominance order. Subject maintains these actions despite unfavorable

consequences or threats from others.

42. Intelligent: Subject is quick and accurate in judging and comprehending both

social and non-social situations. Subject is perceptive and discerning about social

relationships.

43. Protective: Subject shows concern for other gorillas and often intervenes to

prevent harm or annoyance from coming to them.

44. Quitting: Subject readily stops or gives up activities that have recently been

started.

45. Inventive: Subject is more likely than others to do new things including novel

social or non-social behaviors. Novel behavior may also include new ways of

using devices or materials.

46. Clumsy: Subject is relatively awkward or uncoordinated during movements

including but not limited to walking, acrobatics, and play.

32

47. Erratic: Subject is inconsistent, indefinite, and widely varying in its behavior and

moods.

48. Friendly: Subject often seeks out contact with other gorillas for amiable, genial

activities. Subject infrequently initiates hostile behaviors towards other gorillas.

49. Anxious: Subject often seems distressed, troubled, or is in a state of uncertainty.

50. Lazy: Subject is relatively inactive, indolent, or slow moving and avoids energetic

activities.

51. Disorganized: Subject is scatterbrained, sloppy, or haphazard in its behavior as if

not following a consistent goal.

52. Unemotional: Subject is relatively placid and unlikely to become aroused, upset,

happy, or sad.

53. Imitative: Subject often mimics, or copies behaviors that it has observed in other

gorillas.

54. Independent: Subject is individualistic and determines its own course of action

without control or interference from other gorillas.

Subjective Well-Being Questionnaires:

The assessment of subjective well-being in gorillas’ questionnaire was developed

by Dr. James King (Weiss, et al., 2006; King and Landau, 2003) and contains the

following instructions for raters:

This questionnaire has four questions, all relating to the subjective well-being of

the gorillas at your zoo. Each question asks about a different personality dimension or

trait relating to subjective well-being. The following scale should be used to make your

ratings.

33

1. Displays either total absence or negligible amounts of the trait or state.

2. Displays small amounts of the trait on infrequent occasions.

3. Displays somewhat less than average amounts of the trait.

4. Displays about average amounts of the trait.

5. Displays somewhat greater than average amounts of the trait.

6. Displays considerable amounts of the trait on frequent occasions.

7. Displays extremely large amounts of the trait.

The raters were given the additional following instructions.

Please give a rating for each item even if your judgment seems to be based

on a purely subjective impression of the gorilla and you are somewhat unsure

about it. Indicate your rating by placing a cross in the box underneath the chosen

number.

Finally, do not discuss your rating of any particular gorilla with anyone

else. As explained in the handout accompanying this questionnaire, this

restriction is necessary in order to obtain valid reliability coefficients for the traits.

1. Estimate the amount of time the gorilla is happy, contented, enjoying itself, or

otherwise in a positive mood. Assume that at other times the gorilla is

unhappy, bored, frightened, or otherwise in a negative mood.

2. Estimate the extent to which social interactions with other gorillas are

satisfying, enjoyable experiences as opposed to being a source of fright,

distress, frustration, or some other negative experience. It is not the number

of social interactions that should be estimated, but the extent to which social

34

interactions that do occur are a positive experience for the gorilla. Use many

social interactions that you can recall as a basis for your judgment.

3. Estimate, for this gorilla, the extent to which it is effective or successful in

achieving its goals or wishes. Examples of goals would be achieving desired

locations, devices, or material in the enclosure. Keep in mind that each gorilla

will presumably have its own set of goals that may be different from other

gorillas.

4. Imagine how happy you would be if you were that gorilla for a week. You

would be exactly like that gorilla. You would behave the same way as that

gorilla, would perceive the world the same way as that gorilla, and would feel

things the same way as that gorilla.

35

Chapter 3

Results

Personality and Subjective Well-Being Results

Interrater Agreement of Item Ratings

Interrater reliability was estimated using two of Shrout and Fleiss’s (1979)

intraclass correlation coefficients (ICCs): ICC(3,1), which indicate the reliability of

ratings for a typical, single rater, and ICC(3,k), which indicates the reliability for all the

raters(k) averaged together. All ICC’s were calculated with PASW software. Mean

interrater reliabilities for personality and subjective well-being were as high as or higher

than comparable studies on chimpanzees (King and Landau, 2003; King and Figueredo,

1997) and orangutans (Weiss, et al., 2006)

Personality

Interrater reliabilities of the 54 personality items were calculated from data on

eight gorillas that had been rated by 9 raters per gorilla. The reliabilities of individual

ratings, ICC (3,1), ranged from .03 (disorganized) to 0.73 (dominant), with a mean

reliability of 0.30. The reliabilities of mean ratings, ICC (3,k), ranged from 0.28

(thoughtless) to 0.96 (dominant) with a mean reliability of 0.71. See Table 2 on pages

36-37.

Subjective Well-Being

Interrater reliabilities of the four subjective well-being items were calculated from

data on the eight gorillas that were rated by nine raters per gorilla. Individual rating

reliabilities, ICC(3,1), ranged from 0.27 (Goals) to 0.45 (BeGorilla and SWBSUM), with

36

a mean reliability of 0.38. Reliabilities of mean ratings, ICC (3,k), ranged from 0.77

(Happy and Goals) to 0.88 (BeGorilla and SWBSUM), with a mean reliability of 0.83.

See Table 3 on page 37.

Table 2. Interrater Reliabilities for Personality Traits

Personality Trait ICC

(average)

ICC(individual)

Fearful 0.78 0.28

Dominant 0.96 0.73

Persistent 0.94 0.62

Cautious 0.88 0.46

Stable 0.78 0.29

Autistic 0.63 0.16

Curious 0.85 0.38

Thoughtless 0.28 0.04

Stingy 0.74 0.24

Jealous 0.6 0.14

Individualistic 0.65 0.17

Reckless 0.67 0.18

Sociable 0.91 0.54

Distractable 0.78 0.28

Timid 0.88 0.45

Sympathetic 0.74 0.24

Playful 0.86 0.4

Solitary 0.87 0.43

Vulnerable 0.78 0.29

Innovative 0.79 0.29

Active 0.91 0.53

Helpful 0.77 0.27

Bullying 0.85 0.39

Aggressive 0.82 0.34

Manipulative 0.44 0.08

Gentle 0.77 0.28

Affectionate 0.93 0.6

Excitable 0.88 0.44

Impulsive 0.86 0.41

Inquisitive 0.78 0.28

Submissive 0.94 0.62

Cool 0.78 0.28

37

Table 2: continued

Dependable 0.95 0.69

Irritable 0.83 0.35

Predictable 0.4 0.07

Decisive 0.68 0.19

Depressed 0.74 0.24

Conventional 0.7 0.2

Sensitive 0.41 0.07

Defiant 0.8 0.3

Intelligent 0.39 0.07

Protective 0.55 0.12

Quitting 0.46 0.09

Inventive 0.8 0.3

Clumsy 0.29 0.04

Erratic 0.69 0.2

Friendly 0.86 0.4

Anxious 0.71 0.21

Lazy 0.82 0.34

Disorganized 0.22 0.03

Unemotional 0.77 0.27

Imitative 0.57 0.13

Independent 0.86 0.41

Table 3. Interrater and Internal Consistency Reliabilities for Subjective Well-Being

Item ICC(3,K) ICC(3,1) Cronbach’s

Alpha

Happy 0.77 0.28 NA

SocInt 0.87 0.43 NA

Goals 0.77 0.27 NA

BeGorilla 0.88 0.45 NA

SWBsum 0.88 0.45 0.90

38

Principal-Components Analysis

Personality

I conducted a principle-components analysis of the mean personality ratings using

PASW software. An examination of the scree plot suggested three principal components.

Parallel analysis, or a Monte Carlo simulation (Horn, 1965; O’Connor, 2000) done using

SAS software indicated that the eigenvalue of the fourth component failed to exceed the

95th

percentile of eigenvalues expected under chance. Therefore, the principal

components analysis with varimax rotation was re-run specifying for three components

which accounted for 81% of the total variance.

Absolute factor loadings > 0.40 were considered salient (See Table 4 on pages 40-

42). According to this criterion, one item (unperceptive) did not load saliently on any

factor. There was some factorial complexity: 18 items had two salient loadings and 7

items had three salient loadings. In these cases, the item is assigned to the factor that had

the highest loading.

Table 5 on page 43 shows all the personality traits associated with each

personality factor. T-scores were calculated for each gorilla’s score for each personality

factor and are shown in Table 6 on page 43. Using a standard deviation of one rule, each

of the gorillas was given a low, average, or high score for each of the personality factors

(see Table 7 on page 44).

The gorilla personality structure that emerged bore similarities to the Five Factor

Model and chimpanzee and orangutan personality factor structures, but there were several

clear differences.

39

The first factor, dominance, was similar to the chimpanzee (King and Figueredo,

1997) and orangutan dominance factors (Weiss, et al., 2006) and indicates the importance

of this aspect of personality in gorillas, chimpanzees, and orangutans. A dominance

factor is not present in humans.

The second factor of extraversion/agreeableness resembles the extraversion and

agreeableness factors found in humans (Costa and McCrae, 1980; McCrae and Costa,

1991), chimpanzees (King and Figueredo, 1997), and orangutans (Weiss, et al., 2006). It

includes both social aspects of extraversion (i.e. sociable, friendly) and active (i.e.

playful; active) aspects of extraversion (King, pers. comm.).

The third factor, conscientiousness, resembles the conscientiousness factor found

in humans (Nettle, 2006) and chimpanzees (King and Figueredo, 1997). It includes

aggressive, unpredictable, and emotional components and it was not found in orangutans

(Weiss, et al., 2006). See Table 5 on page 43 for the personality traits found in each

factor.

Subjective Well-Being

I conducted a principle components analysis of the mean ratings of the four

subjective well-being items. Only the first factor had an eigenvalue > 1.00 and this factor

accounted for 85% of the total variance. All four items had loadings > 0.40. In addition,

the four subjective well-being items were significantly highly correlated (see Table 8 on

page 44) and therefore each gorilla’s subjective well-being score was defined as the

summation of the mean ratings for all four items (Weiss, et al., 2006; King and Landau,

2003).

40

Table 4. Factor Structure of Mean Adjectival Ratings

Item DOM EXTRA CONSCIEN

Fearful -.973 .029 -.137

Decisive .958 .044 .179

Submissive -.956 -.041 .074

Dominant .954 -.081 .010

Vulnerable -.932 -.056 .013

Timid -.917 -.153 .204

Persistent .916 .282 .010

Bullying .915 -.117 -.276

Independent .895 -.163 -.204

Stingy .880 .011 -.271

Aggressive .846 -.259 -.430

Dependable -.832 .492 .096

Cautious -.797 -.321 .348

Inventive .793 .412 .030

Anxious -.751 -.120 -.272

Innovative .703 .587 .143

Quitting -.649 -.455 -.354

Distractable -.621 .199 .236

41

Table 4: continued

Intelligent .597 .176 .196

Imitative -.555 .492 .173

Thoughtless -.527 -.151 .050

Clumsy -.501 .088 .311

Disorganized -.431 .238 .210

Active -.189 .950 -.155

Sociable -.153 .940 .201

Playful -.076 .926 -.012

Solitary -.120 -.920 .003

Conventional -.203 -.912 .274

Lazy .030 -.894 .064

Depressed -.034 -.894 .226

Friendly -.225 .824 .465

Helpful -.403 .818 .372

Inquisitive .538 .791 -.186

Unemotional -.133 -.788 .451

Curious .464 .776 -.281

Affectionate -.393 .770 .419

42

Table 4: continued

Sympathetic -.453 .742 .445

Manipulative .492 .723 -.030

Protective .061 .626 .478

Jealous .577 .617 -.486

Reckless .399 .609 -.556

Individualistic .494 .599 -.196

Erratic .059 -.075 -.956

Stable .401 -.093 .897

Impulsive .296 .278 -.848

Irritable .189 -.384 -.843

Excitable .145 .456 -.841

Gentle -.490 .325 .800

Predictable -.140 -.648 .744

Cool .427 -.349 .741

Defiant .501 .350 -.728

Autistic -.162 -.011 -.653

Sensitive -.547 .279 .603

Salient items are in boldface. DOM=Dominant factor; EXTRA=

Extraversion/Agreeableness factor; CONSCIEN=Conscientiousness factor

43

Table 5. Items Defining Each of the Three Gorilla Personality Factors

Dominance Extraversion/Agreeableness Conscientiousness

-Fearful +Active -Erratic

+Decisive +Sociable +Stable

-Submissive +Playful -Impulsive

+Dominant -Solitary -Irritable

-Vulnerable -Conventional -Excitable

-Timid -Lazy +Gentle

+Persistent -Depressed +Predictable

+Bullying +Friendly +Cool

+Independent +Helpful -Defiant

+Stingy +Inquisitive -Autistic

+Aggressive -Unemotional +Sensitive

-Dependable +Curious

-Cautious +Affectionate

+Inventive +Sympathetic

-Anxious +Manipulative

+Innovative +Protective

-Quitting +Jealous

-Distractible +Reckless

+Intelligent +Individualistic

-Imitative

-Thoughtless

-Clumsy

-Disorganized

Table 6. T-scores for the Three Gorilla Personality Factors

Gorilla Dominance Extraversion/Agree Conscientiousness

Shango 48 34 62

Barney 59 47 52

Tommy 45 45 37

Billy 61 46 34

Matt 61 55 57

Virgil 51 68 48

Jabir 42 57 50

Samson 33 48 59

44

Table 7. Factor Profiles for the Sedgwick County Zoo Gorillas

Gorilla Dominance Extraversion/Agree Conscientious

Shango AVE LOW HIGH

Barney HIGH AVE HIGH

Tommy AVE AVE LOW

Billy HIGH AVE LOW

Matt HIGH HIGH HIGH

Virgil HIGH HIGH AVE

Jabir AVE HIGH AVE

Samson LOW AVE HIGH

Table 8. Correlations among Four Items on Subjective Well- Being

Questionnaire

ITEM 1 2 3

1 HAPPY

2 SOCINT .89**

3 GOALS .79* .56

4 BEGORILLA .87** .87** .80*

*p<.05 **p<.01

45

Hypothesis and Prediction Results

Hypothesis 1: Personality predicts behavior in captive gorillas (See Table 14 on

Pages 65-66).

Prediction 1: Dominance will be positively correlated with aggressive behaviors

(DISPLACE; NCA; CA; NCAVIS; AGON).

A. Dominance will be positively correlated with aggressive behavior

(displace; non-contact aggression; contact aggression; non-contact aggression

towards visitors).

ACCEPT. (r=0.68; p<0.5; one-tailed).

B. Dominance will be positively correlated with displacement rates.

ACCEPT. (r=0.81; p<.01; one-tailed).

C. Dominance will be positively correlated with non-contact aggression rates.

. REJECT. (r=0.38; not significant; one-tailed).

D. Dominance will be positively correlated with contact aggression.

REJECT. (r=0.58; not significant; one-tailed).

E. Dominance will be positively correlated with non-contact aggression

towards visitors.

REJECT. (r=-0.03; not significant; one-tailed).

Prediction 2: Extraversion will be positively correlated with affiliation.

(PLAY; GROOM; TOUCH; SEX; APPROACH(ALL); APPROACH(ME);

APPROACH VISITORS; APPROACH GORILLAS).

A. Extraversion will be positively correlated with affiliation(play;

groom; touch; sex; approach(all); approach(me); approach(gorillas).

ACCEPT. (r=0.74; p<.05; one-tailed).

B. Extraversion will be positively correlated with play.

ACCEPT. (r=0.76; p<.05; one-tailed).

46

C. Extraversion will be positively correlated with groom.

REJECT. (r=0.37; not significant; one-tailed).

D. Extraversion will be positively correlated with touch.

ACCEPT. (r=0.74; p<.05; one-tailed).

E. Extraversion will be positively correlated with sex.

REJECT. (r=0.44; not significant; one-tailed).

F. Extraversion will be positively correlated with approach(all).

ACCEPT. (r=0.89; p<.01; one-tailed).

G. Extraversion will be positively correlated with approach(me).

REJECT. (r=0.32; not significant; one-tailed).

H. Extraversion will be positively correlated with approach(visitors).

REJECT. (r=0.52; not significant; one-tailed).

I. Extraversion will be positively correlated with approach(gorillas).

ACCEPT. (r=0.85; p<.01; one-tailed).

Hypothesis 2: Personality predicts vocal behavior (vocal profile) in captive gorillas.

(See Table 14 on pages 65-66).

Prediction 1: There will be a positive relationship between dominance and vocal rate.

REJECT. (r=0.35; not significant; one-tailed).

Prediction 2: There will be a positive relationship between dominance and syllabled call.

rate.

REJECT. (r=0.52; not significant; one-tailed).

Prediction 3: There will be a negative relationship between dominance and non-syllabled

call rate.

ACCEPT. (r=-0.68; p<.05; one-tailed).

47

Prediction 4: There will be a positive relationship between dominance and double grunt

rate.

REJECT. (r=0.58; not significant; one-tailed).

Hypothesis 3: Personality predicts subjective well-being in captive gorillas.

(See Table 16 on page 69).

Prediction 1: There will be a positive relationship between extraversion and

subjective well-being sum.

ACCEPT. (r=0.78; p<.05; one-tailed).

Prediction 2: There will be a positive relationship between dominance and an

ability to achieve goals.

ACCEPT. (r=0.88; p<.01; one-tailed).

Hypothesis 4: Subjective well-being explains vocal behavior (vocal profile) in

captive gorillas. (See Table 15 on pages 67-68).

Prediction 1: Captive gorillas will have a lower vocal rate than wild gorillas.

REJECT. (see explanation below)

What is the Vocal Rate for Captive Gorillas?

Harcourt et al., (1993) found that the vocal rate of wild adult mountain gorilla

males was fourteen vocalizations per hour. However, it should be kept in mind that they

excluded pig grunts and laughing in their analysis. Both my captive study and the

Gibeault captive study included those two types of close calls in their vocal rates

(Gibeault, unpublished manuscript). My study found that captive adult male western

gorillas vocalized at a rate of 11.88 vocalizations per hour with a range of 8.74 vocs/hr-

15.30 vocalizations per hour (See Table 9 on page 49). A one-sample t-test showed that

the vocalization rate of captive adult males in the Schaefer study does not differ

48

significantly from that of wild adult male gorillas (one sample t-test: t(4): -1.619,

p=0.181). A one-sample t-test was used because we do not have the raw data for the wild

silverback vocalization rate. In addition, a one-sample t-test showed that the adult

captive males in the Gibeault study did not vocalize at a significantly different rate from

that of wild gorillas (one sample t-test: t(4): 1.607, p=0.183). The average for adult

males in the Gibeault study was 22.22 vocalizations per hour with a range of 10.63-40.34

vocalizations per hour (see Table 10 on page 50). In addition, an independent samples t-

test showed that there was not a significant difference in vocal rate between the two

captive studies (Schaefer and Gibeault) (t(8)=-1.917,p=.092). See Figure 1 on page 51.

A t-test, rather than a Mann-Whitney test was used because the data were tested for

normality and was found to not be significantly different from a normal distribution.

Lastly, the age/sex composition of the Harcourt study should be noted: one silverback

lived with six adult females and several immatures; two silverbacks lived together with

three to four adult females and several immatures (Harcourt and Stewart, 2001). In other

words, one silverback lived in a one-male family group while the other two silverbacks

liver in a multi-male family group.

Furthermore, this study showed that there is a statistically different mean vocal

rate for silverbacks and blackbacks. The mean vocal rate for silverbacks in this study

was 11.88 vocalizations per hour. The mean vocal rate for blackbacks in this study was

6.86 vocalizations per hour. See Figure 2 on page 52. Neither the Gibeault captive study

(Gibeault, unpublished manuscript) nor the Harcourt et al. (1993) wild study had

blackbacks in their study so there are no other blackback rates for comparison.

49

Prediction 2: There will be a positive relationship between subjective well-being

and vocal rate.

REJECT. (r=-0.25; not significant; one-tailed).

Prediction 3: There will be a significant positive relationship between subjective

well-being and contentment calls (double grunt; rumble).

REJECT. (double grunt: r=0.17; not significant; one-tailed; rumble: r=-0.31; not

significant; one-tailed).

Table 9. Mean Vocal Rates of Sedgwick County Zoo Gorillas

Name Age Vocs per hour

Shango SB 11.16

Barney SB 8.74

Tommy SB 15.30

Billy SB 11.73

Matt SB 12.45

Virgil BB 7.09

Jabir BB 6.07

Samson BB 7.41

50

Table 10. Mean Vocal Rates for Silverbacks in Gibeault Study

Silverback # Zoo Group Type Vocs per hour

SB 1 Toronto Family 10.63

SB 2 Granby Family 40.34

SB 3 Granby Solitary 15.26

SB 4 Buffalo Family 24.94

SB 5 Buffalo Solitary 19.94

Note: SB 2 and 3 were housed next to each other

51

52

53

OTHER RESULTS THAT PROVIDE INSIGHT INTO THE MEANING OF

GORILLA CALLS

What is the Vocal Repertoire of Captive Gorillas?

My study found that captive silverbacks and blackbacks give all the calls that wild

silverbacks and blackbacks give. In addition, there are two new types of calls in this

study that have not been documented in wild gorillas (Fossey, 1972; Harcourt et al.,

1993) but were documented in another captive study (Gibeault, unpublished manuscript).

These two new calls are the Quadruple Grunt and the Multiple Grunt. The Gibeault study

(which also differentiated calls by the naked ear) contained Quadruple and Multiple

Grunts (those of five to nine beats), however, the beats or syllables were of the same,

short duration. In contrast, in my study the Quadruple and Multiple Grunts had specific

rhythms to them that can be found in Western music and Homeric epics. In addition,

this study documents two new variations of the Hoot plus Chest Beat call because the

gorillas substitute items in their captive environment for the chest beat. For example,

they drum on the window in the same rhythms as a typical chestbeat or they will slam a

rope cord into a metal door in place of the chestbeat. For obvious reasons, these two

modifications of the Hoot plus Chest beat call have not been heard in wild gorillas.

See Table 11 on page 54 for a complete list of the vocal repertoire of the

Sedgwick County Zoo gorillas and the hypothesized equivalent call and its name that

have been documented for wild mountain gorillas. In addition, this study documents the

vocal repertoires of each of the eight gorillas individually (See Figures 3-10 on pages 55-

62). See Table 12 on page the rate of non-syllabled calls and syllabled calls on page 63

and Table 13 on page 64 for the use of each call by age class and hypothesized contexts.

54

Table 11. Vocal Repertoire of Sedwick County Zoo Gorillas and

Hypothesized Equivalent Call in Mountain Gorillas

Number SCZ call Abbreviated

Code

Mountain

Gorilla Call

1 Purr/Single Grunt PUR/SG Single

Grunt/Belch

2 Double Grunt DG Double

Grunt/Belch

3 Inverse Grunt IG Inverse Double

Grunt/Belch

4 Triple Grunt TG Triple

Grunt/Belch

5 Quadruple Grunt QG Not heard in

mountain gorillas

6 Multiple Grunt MG Not heard in

mountain gorillas

7 Pig Grunt PIG G Cough Grunt/Pig

Grunt

8 Chutter CHUT Whiny/Neigh

9 Rumble RUM Belch variant

10 Sing/Grumble SING/GRUM Hum, High

Hum/Grumble

11 Train Grunt TRAIN G Train

grunt/copulatory

pants

12 Laugh LAUGH Chuckle

13 Hoot HOOT Hoot Series

14 HootChestBeat HOOTCB Hoot series with

ChestBeat

15 HootDrumWindow HOOTDW Not heard in

mountain gorillas

16 HootSlam HOOTSLAM Not heard in

mountain gorillas

17 Hoot Bark HOOTBARK Hoot Bark

18 Hiccup Bark HICBARK Hiccup Bark

19 Growl GROWL Growl

20 Scream SCREAM Scream

55

56

57

58

59

60

61

62

63

Table 12. Non-Syllabled and Syllabled Vocalization Rates

Name NS VOC/HR S VOC/HR

Shango 1.48 9.26

Barney 2.22 6.52

Tommy 0.27 14.05

Billy 0.42 11.09

Matt 0.26 12.22

Virgil 3.82 3.19

Jabir 4.46 1.52

Samson 4.91 2.49

64

Table 13. Calls and Associated Age Classes and Contexts

R=rest; F=feed; M=move; P=play; S=sex; AG=agonistic/spacing

Ap=approach; AL=alarm; NC=non-contact aggression

* used rarely by that age class (n=1-5 in 7.5 months).

Call SB BB R F M P S AG AP AL NC

Purr/SG X X X X X X X

DG X X X X X X

IG X X X X X

TG X X X X X

QG X X X

MG X X X

PG X X X X

CHUT X X* X

RUM X X

SING/GRUM X X X

TRAIN X X X

LAUGH X X X

HOOT X X X

HOOTCB X X

HOOTDW X X

HOOTSLAM X X

HOOTBARK X* X

HICBARK X* X

GROWL X* X

SCREAM X* X

65

SUMMARY OF ALL CORRELATIONS BETWEEN PERSONALITY

AND BEHAVIOR (all correlations from predictions were one-tailed; all others

were two-tailed).

Table 14. Correlations between Personality Dimensions and Behaviors

BEHAVIOR DOM EXTRA CONSCIEN

DISPLACE .81** .18 -.32

NCA .38 -.42 .24

CA .58 .59 .04

NCAVIS -.03 .14 -.69*

PLAY -.45 .76* .31

GROOM .09 .37 .22

TOUCH -.51 .74* .30

SEX -.73* .44 .33

APPROACH

(ALL)

-.27 .89** .09

APPME .25 .32 -.58

APPVIS .32 .52 -.48

APPGOR -.29 .85** .20

SOLOPLAY -.28 .80* -.04

VOCRATE .35 -.49 -.38

NSVOCRATE -.68* .43 .39

66

Table 14: continued

SVOCRATE .52 -.47 -.38

CHUT .23 -.21 -.76*

PURR .24 -.77* -.23

PIG G -.56 .02 .08

DG .58 -.16 -.64

RUM .34 -.56 .21

HOOT -.02 -.35 -.35

SING -.75* .50 .27

LAUGH -.27 .84** .09

AGON .68* -.22 .05

AFFIL -.48 .74* .32

PUBLICORIEN

(NCA&APP)

-.01 .17 -.70*

*p<.05; **p<.01

67

SUMMARY OF ALL CORRELATIONS BETWEEN SUBJECTIVE

WELL-BEING SUM AND BEHAVIOR (correlations from predications were

one-tailed; all others were two-tailed).

Table 15. Correlations between Subjective Well-Being and Behaviors

BEHAVIOR SWBSUM

DISPLACE .58

NCA -.20

CA .71*

NCAVIS -.10

PLAY .46

GROOM .54

TOUCH .40

SEX .02

APPROACH (ALL) .62

APPME .23

APPVIS .52

APPGOR .61

SOLOPLAY .47

VOCRATE -.25

NSVOCRATE -.01

68

Table 15: continued

SVOCRATE -.13

CHUT -.16

PURR -.55

PIG G -.34

DG .17

RUM -.31

HOOT -.37

SING .02

LAUGH .60

AGON .14

AFFIL .42

PUBLICORIEN (NCA &APP) -.07

*p<.05 **p<.01

69

SUMMARY OF ALL CORRELATIONS BETWEEN PERSONALITY AND

SUBJECTIVE WELL-BEING (all correlations from predictions were on-tailed;

all others were two-tailed).

Table 16. Correlations between Personality and Subjective Well-Being

DOM EXTRA CONSCIEN

HAPPY .52 .76* .03

SOCINT .20 .93** -.04

GOALS .88** .34 -.06

BEGORILLA .59 .79* -.22

SWBSUM .58 .78* -.08

*p<.05 **p<.01

70

Chapter 4

Discussion

Can Personality and Subjective Well-Being Inform Our Understanding of the

Meaning of Gorilla Vocalizations?

The main goal of this dissertation was to try to get a better understanding of the

meaning of gorilla vocalizations by looking at an individual’s personality dimensions and

measures of subjective well-being. If gorilla calls, like human speech, provide

information that is both semantic and emotional (Seyfarth and Cheney, 2003), then we

can expect to learn more about the meaning or function of gorilla calls by looking at

correlations between certain personality dimensions and rates of particular calls (i.e. the

vocal profile) and between subjective well-being and the rates of particular calls (i.e. the

vocal profile).

Reliability and Validity of Personality and Subjective Well-Being Measures

Before discussing the principal results of my dissertation I need to establish that

my study has high levels of reliability and validity for its personality and subjective well-

being measures (Freeman and Gosling, 2010).

For my study, the mean of the inter-rater reliability of the 54 personality adjective

traits as measured by the ICC (3,k) was 0.71, which is higher than the reliability mean in

the nonhuman primate studies (0.64; Freeman and Gosling, 2010) and the orangutan

study (0.64; Weiss, et al., 2006). However, the mean of my study was lower than the

mean inter-rater reliability of the six personality dimensions of chimpanzees (0.82).

(Pederson, et al., 2005). For my study, the mean of the inter-rater reliability of the four

subjective well-being facets as measured by the ICC (3,k) was 0.83, which is higher than

71

the mean inter-rater reliability of the chimpanzee study (r=0.66; King and Landau, 2003)

and higher than that for studies of humans (0.32; Parot and Diener, 1993). In addition for

my study, the internal consistency measure of the summation of the four subjective well-

being measures as measured by Cronbach’s alpha was 0.90 which is higher than that for

the chimpanzee study (0.86; King and Landau, 2003), and the orangutan study (0.82;

Weiss, et al., 2006) and studies of humans (0.81; Okun, and Stock, 1987; 0.77; Sandvik

et al., 1993).

Validity is an index of how well an instrument is measuring what it is designed to

measure (Freeman and Gosling, 2010). The best way to demonstrate validity is to have

strong significant correlations between personality dimensions and behaviors that are

expected to be associated with those personality dimensions (Pederson, et al., 2005).

This is called convergent validity (Freeman and Gosling, 2010). The mean significant

correlation between personality and behavior in my study was 0.76 which is much higher

than the mean in the chimpanzee study (0.35; Pederson, et al., 2005), all nonhuman

primate studies (0.25; Freeman and Gosling, 2010), and those studies on humans (range:

0.1-0.3; Meyers, et al., 2001).

Principal Results

Personality Predicts Vocal Behavior (Vocal Profile) in Captive Gorillas

Harcourt and Stewart (2001) showed that dominant gorillas vocalize more than

subordinate gorillas, and gave more syllabled calls, specifically double grunts, than

subordinate gorillas. They also showed that subordinate gorillas tend to give more non-

syllabled calls than more dominant gorillas (Harcourt and Stewart, 2001). This study

showed that gorillas that scored higher on the dominance personality dimension had a

72

higher vocal rate than those that scored lower on the dominance personality dimension,

although it did not reach statistical significance (r=0.35). This corroborates the Harcourt

and Stewart (2001) findings that syllabled calls, and specifically double grunts function

as a signal of dominance in gorillas and that non-syllabled calls function as a signal of

submission in gorillas. In addition, this study corroborates Sicotte’s hypothesis that the

chutter call functions as an agonistic or spacing call, specifically given to females by their

silverbacks when they move away from them (Sicotte, 2001) and functions to get the

female to stay in close proximity to them. In this study the chutter was given to me when

I moved away from a blackback that spent a great deal of time in proximity to me. My

study also provides support for my hypothesis that the chutter functions as a close range

threat call given to group outsiders to induce them to back off. Specifically, in this study

it is given most frequently to zoo visitors. Tommy and Billy gave many chutter calls to

zoo visitors when they were in the public dayroom and never gave chutters when they

were off-exhibit in the non-public dayroom. The chutter is an agonistic call in both

contexts, when given to outsiders and females, with an intent to induce the recipient of

the call to back off, or increase their distance to the caller in the first instance, and with an

intent to induce the recipient of the call to stay close, or decrease their distance to the

caller in the latter instance. My proposed function of the chutter calls supports some of

the Gorilla Foundation staff’s idea that the chutter call is given when the gorillas are

stressed or upset (Gorilla Foundation staff, pers. comm.) about the movements, presence,

or behaviors of those around them.

The dominance personality dimension was significantly negatively correlated

with singing and significantly negatively correlated with the non-syllabled vocalization

73

rate. This provides support for my assertion that singing is given by blackbacks as a way

of expressing submission. In general, more submissive gorillas give more non-syllabled

calls than syllabled calls and this lends support for my assertion that they serve as

appeasement and submissive signals.

The extraversion/agreeableness personality dimension was significantly

negatively correlated with the purr/single grunt vocalization and significantly positively

correlated with the laugh vocalization. Blackbacks tend to score higher than silverbacks

on scores of extraversion (Stoinski, et al., 2004) and have higher rates of play than

silverbacks (Stoinski, et al., 2004). Since the laugh vocalization is given during play only

it makes sense that as rates of laughter go up, so do scores of extraversion/agreeableness.

Silverbacks tend to give syllabled calls such as the purr/single grunt more than

blackbacks and also tend to be less extraverted than blackbacks so it makes sense that

there is a negative correlation between these items.

The conscientiousness personality dimension was significantly negatively

correlated with the rate of chutters, an agonistic call usually given to zoo visitors. The

silverbacks, Tommy and Billy both scored low on conscientiousness and have high rates

of giving chutters. The silverbacks Shango and Barney both scored high on

conscientiousness and have low rates of giving chutters. These facts provide support for

my assertion that the chutter call is given to non-group members as a way of telling them

to back off or stop their offensive behavior. Shango and Barney are very cool and calm

and laid back silverbacks and do not give any non-contact aggression or chutters to the

zoo visitors. Tommy and Billy are the exact opposite. They give a lot of non-contact

aggression and chutters to the zoo visitors and are the opposite of calm and cool.

74

Subjective Well-Being Does Not Predict Vocal Behavior (Vocal Profile) in Captive

Gorillas

This study found that contrary to the accepted wisdom, captive gorillas do not

vocalize less than wild gorillas. In addition, there is no relationship between subjective

well-being and vocal rate in gorillas. Lastly, there is no relationship between subjective

well-being and contentment calls (double grunt; rumble). Subjective well-being did not

predict any behavior except for contact aggression (r=0.71). The significant positive

correlation between subjective well-being and contact aggression is counter intuitive but

might be explained by the significant positive relationship between extraversion and

contact aggression in gorillas (Kuhar, et al., 2006) and the significant positive

relationship between subjective well-being sum and extraversion in my study. In other

words, the relationship between subjective well-being and contact aggression is

epiphenomenal to the relationship between extraversion and contact aggression. My

study also found a positive relationship between extraversion and contact aggression but

it did not reach statistical significance (r=0.59).

Vocal Rates of Captive Gorillas:

This study found that captive gorillas do not vocalize significantly less than wild

gorillas as previously thought. The extremely high rate of 40.34 vocalizations per hour

from the Gibeault study can be explained by the unnatural housing conditions of the

gorillas. The silverback that vocalized 40 times an hour lived in a family group and was

housed next to a solitary male who had a female that was being introduced to him. So

sometimes the female was with the solitary male and sometimes she was with the family

group.

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The vocal rate results of this study are positive in the sense that captive gorillas’

vocal behavior may not be aberrant as previously thought. However, we don’t have vocal

profiles for individual wild gorillas with which to compare the use of specific calls.

These data would be necessary to compare the rate of agonistic versus more pro-social

calls. One of the most important findings of this study is that captive gorillas do vocalize

and do so at a rate not significantly different from that of wild gorillas (Harcourt and

Stewart, 2001). Perhaps this study will help keepers and curators to be more sensitive to

the gorillas’ vocalizations and their proposed meanings and work to increase pro-social or

contentment calls and decrease agonistic or stress-related calls.

Limitations of this Study:

One obvious limitation of this study is the small sample size of eight gorillas. I

think that statements C-E under Prediction 1 of Hypothesis 1 (see page 45) would have

been accepted instead of rejected had the sample size been larger. This is indicated by

the fact that the conglomerate category of all aggressive behaviors (statement A under

prediction 1 and Hypothesis 1 on page 45) was significantly positively correlated with

dominance, even though most of the individual categories were rejected when analyzed

apart from each other (statements C, D, E under prediction 1 of Hypothesis 1 on page

45). Additionally, the conglomerate category of all affiliative behaviors (statement A

under prediction 2 under Hypothesis 1 on page 45) was significantly positively correlated

with extraversion despite the fact that most of the individual categories (statement C-I

under prediction 2 of Hypothesis 1 on page 46) were rejected when analyzed apart from

each other .In addition, I only looked at male gorillas and not females. By studying

female gorillas we may find that a more diversified or different personality structure

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exists for gorillas. In addition, captive male gorillas may vocalize differently to females

and immature than they do to other males. By studying males that live in family groups

we will get a more complete understanding of the vocal repertoire of captive gorillas. My

study also only looked at the gorillas at one zoo, so at this time, we do not know if these

results can be generalized to all gorillas. However, I think the benefits of focusing on one

population far outweigh the negatives.

Broader Implications of this Study

Personality and Vocal Communication in Gorillas:

My study showed that humans can reliably assess personality and subjective well-

being in gorillas. My study had high means for inter-rater reliability and validity for both

personality and subjective well-being (Freeman and Gosling, 2010; King and Landau,

2003). This provides support for the idea that zoos can use quicker and less expensive

personality and subjective well-being questionnaires instead of expensive, long-term

multi-institutional behavioral studies to make captive management decisions (Kuhar, et

al., 2006).

One significant finding of this study is that the conscientiousness personality

dimension is more ancient that previously thought (Gosling, 2008; King, pers. comm.).

Instead of originating with the chimp/bonobo clade roughly 5-7 million years ago, it

arose with the last common ancestor of gorillas and the hominin clade around 8-9 million

years ago (Jurmain, et al., 2009). It has been documented in all of the great apes except

for orangutans (King, pers. comm.). What then are the selective pressures that gave rise

to the conscientiousness personality dimension in the ancestors of the African great apes?

Perhaps, the importance of strong bonds that persist into adulthood in the African great

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apes and that are absent in orangutans placed a selective premium on being able to

interact with others in a non-aggressive and consistent manner. The conscientiousness

personality factor involves three main facets: aggressiveness (irritable); predictability

(erratic, impulsive, predictable, reckless); and emotionality (excitable, stable, cool)

(King, pers. comm.) In chimpanzees, there are strong bonds between adult males that are

often related since there is male philopatry and these males hunt and protect the

community’s territory together. In bonobos, there are strong bonds between adult

females that are not-related and less frequently between adult males and adult females.

In addition, males maintain a strong bond with their mothers throughout their life and

inherit their mother’s standing in the community. In gorillas, there are strong bonds

between the adult females and their preferred silverback and females rely on the

silverbacks for protection. In contrast, orangutans do not have strong bonds with other

adults. Adult males are intolerant of one another. Adult males have their own territories

and adult females have their own territories.

Another explanation for the existence of a conscientiousness factor in the African

apes and not orangutans is the fact that the African apes live in groups and the orangutan

is semi-solitary. The fission-fusion social organization of chimpanzees and bonobos

requires social interaction with a variety of individuals and its fluidity requires a certain

social finesse. However, for orangutans, not much social interaction beyond the mother-

infant bond is necessary. The African apes are the only great apes to have stable, long-

term relationships in adulthood (de Waal, 2006).

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Is Vocal Repertoire Indicative of Subjective Well-Being of Captive Gorillas?

The gorillas of the Sedgwick County Zoo give all the calls that have been

documented in wild silverbacks and blackbacks. In addition, one silverback in this

population gives quadruple grunts and multiple grunts, or grunts of five to nine beats.

These calls have not been heard in any wild gorilla populations but have been

documented in another captive study of gorillas (Gibeault, unpublished manuscript).

There is a difference, however, in the length of the notes of these grunts in the two

captive studies. Matt’s Quadruple grunts and multiple grunts have basic rhythms to them

and the notes vary in their duration. The quadruple grunts and multiple grunts of the

Gibeault study have notes of the same duration with no particular rhythmic quality to

them (Gibeault, unpublished manuscript). This I argue is evidence for the existence of

vocal cultures in captive gorillas. In addition, many of the silverbacks at the Sedgwick

County Zoo incorporate their environment into their natural calls. Examples of this are

the Hoot Drum Window and the Hoot Slam. So the gorillas replace the chest beat with

drumming on the window or slamming a rope cord against a metal door. This type of

modulation of natural calls was not documented in the Gibeault captive study but a

similar phenomenon has been documented in captive gibbons (Geissmann, 2009).

The main difference between the vocal repertoire of captive and wild gorillas is

that the most commonly given vocalization of wild silverbacks is the double grunt and in

this study, the purr/single grunt and chutters, were the most commonly given

vocalizations of the silverbacks. This again is most likely a cultural phenomenon but

could also indicate stress or contentment levels in these captive gorillas. The high use of

chutters from Tommy and Billy indicate that they are stressed and or upset a good deal of

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the time, usually due to the presence of visitors. They never give chutters when they are

in the non-public dayroom where there are no visitors. Dian Fossey (1972; 1983) thought

that double grunts were given by the gorillas to indicate contentment. However, this

study did not demonstrate a significant relationship between the rate of double grunts and

subjective well-being. This may be due to the fact the subjective well-being as measured

in this study involves a more global evaluation of one’s life and other needs besides the

pleasure or contentment obtained when feeding.

Vocal Traditions (Culture) and Vocal Learning in Captive Gorillas

Evidence for the presence of cultural traditions has been presented for many

captive and wild populations of the great apes (Hardus, et al., 2009; Stoinski and van

Schaik, 2006; Wrangham, et al.,1994). Specifically for gorillas, the use of tools has been

demonstrated in the wild (Breuer, et al., 2005) and the presence of behavioral traditions

has been documented in many captive populations (Stoinski and van Schaik, 2006). The

presence of vocal traditions or vocal cultures has not been documented in captive gorillas

so this dissertation is the first to do so. Vocal cultures have been documented in whales

already (Rendell and Whitehead, 2001) so it is not unreasonable to assert that captive

gorillas could also have different vocal cultures.

The presence of innovative vocalizations in captive gorillas also lends support to

the idea that all gorilla vocalizations are not innate or instinctual. The presence of the

quadruple grunts and multiple grunts lend support for the concept of learning or imitation

in some gorilla vocalizations. Most likely Matt heard these calls from another gorilla in

his previous settings or he adopted them from listening to human music.

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This study also provides evidence for vocal learning in captive gorillas. The

silverbacks, Tommy and Matt, both showed evidence for vocal learning during my 7.5

months with them. Tommy adopted my “Kiss” sound that I would give to the gorillas at

the end of the day and sometimes in greeting. One day, Billy scared me with a display

and it caused me to start crying quietly. Tommy had seen Billy display and could hear

and see me crying. I think he gave my “Kiss” sound as a way to comfort me. Matt

adopted the “Pok Pok” sound of the former lead gorilla keeper and started to give this call

during play around 3 months after the lead keeper’s departure. This type of vocal

learning has been documented in captive orangutans (Wich, et al., 2009) and wild

chimpanzees (Boesch, 1991) and provides more support for the idea that the calls of great

apes are learned and not innate.

The Origins of Music and Language in Gorilla Vocalizations

This study documents the first case of singing behavior in the great apes besides

humans (Hauser and McDermott, 2003). Harcourt and Stewart (2001) documented that

all age/sex classes of wild mountain gorillas hum (what I call singing) but their study is

never referred to when examples of species that sing are noted in the literature. In this

study only the blackbacks sang (in scales and with individually distinctive voices), while

the silverback of the group added rhythmic multiple grunts to create a vocal chorus

analogous to human communal singing. Communal singing in humans is known to

produce endorphins and oxytocin and it is reasonable to hypothesize that it also produces

these chemicals in one of our closest relatives, the gorilla. Oxytocin produces trust

amongst humans and other non-human animals (Kosfeld, et al., 2005) and I argue that it

could also be produced during the gorillas’ vocal choruses. Gorilla singing supports the

81

hypothesis of a singing stage in the evolution of human vocal communication in which

synchronous chorusing was used as a means to express emotions, enhance group

solidarity, and accomplish social ends (Mithen, 2006; Dunbar, 2004; Merker, 2000;

Richman, 2000; Richman, 1993; Livingstone, 1973). Gorillas can be used as a model for

how our ancestors communicated prior to the evolution and language and speech. Much

of human singing involves the rhythmic and melodic chanting of nonsense syllables, like

the singing of the !Kung and the Mbuti cultures, which have no text (Richman, 1993). In

this study, individuals of Matt’s group sang prior to being fed. All that was needed was

an auditory cue that their food was coming (such as the food being bounced up and down

in the buckets) or the visual cue of the keepers holding the food buckets in order for the

vocal chorus to begin. I argue that singing in gorillas is comparable to the sexual

behavior in bonobos at a large food patch, which has a calming effect on group members

in a situation that could be potentially aggressive (de Waal, 2006), and serves the same

function. It is a ritual in which the gorillas solidify their roles as subordinate blackbacks

by singing (a non-syllabled vocalization) and as the dominant silverback by giving

syllabled multiple grunts. Harcourt et al. (1993) argued that dominant gorillas tend to

give more syllabled grunts while subordinate gorillas tend to give more non-syllabled

calls, such as the singing. The vocal chorus in Matt’s group is a good example of this.

The syllabled calls, such as Matt’s multiple grunts, can be said to serve as an exaggerated

announcement of the dominant animal’s presence, location, and/or status. Non-syllabled

calls indicate a subordinate gorillas’ submission to the dominant animals. By singing, the

blackbacks ease potential group tensions that could arise with a limited food supply. This

is why, when the silverback Matt approaches the blackbacks while feeding, they sing, and

82

by doing so reduce the likelihood that he will steal all their food away or chase them

away with pig grunts. With their singing, they appease Matt, and in turn both dominant

and subordinate animals can feed in close proximity to each other peacefully. In

addition, when the blackbacks approach Matt at his food patch they also sing, again, to

show their submission and to increase the likelihood that he will allow them to feed near

him. Ritual, as defined by Roy Rappaport (1973) is “conventional acts of display through

which one or more participants transmit information concerning their physiological,

psychological, or sociological states either to themselves or to one or more of their

participants” and it is not too much of a stretch to apply this definition to the singing

behavior of one of our closest relatives in the presence of large amounts of food. As

Peter Marler argued, no animal signal is purely referential or purely emotional (Marler, et

al., 1992) and in this case, the gorillas’ singing and multiple grunts are referential in that

they only do it in the presence of food, so it is referring to the food, and it is emotional in

that it most likely reflects their joy and happiness at the presence of food.

This study is also the first to document the occurrence of rhythmic multiple grunts

(grunts with five to nine syllables) in gorillas. Neither quadruple grunts nor multiple

grunts (grunts with five to nine syllables) have ever been documented in wild gorillas. In

another study of captive gorillas (Gibeault, unpub. man.), quadruple and multiple grunts

were heard, but the syllables were all of the same duration. In contrast, in the quadruple

and multiple grunts heard in this study, the syllables had a specific rhythm and varied in

duration. For example, in the quadruple grunt, the first three syllables, or beats, were of

the same duration while the fourth beat, was much longer. It is equivalent to the opening

phrase of Beethoveen’s fifth symphony which is composed of three short notes followed

83

by a long note. In the 5-grunt, there are three short notes, then a long note, then another

short note; in the 6-grunt there are 3 short notes, the fourth note is a medium duration,

then the fifth and sixth note are both long; in the 7-grunt the first three notes are a triple,

the fourth and fifth notes are a double, the sixth note is very long, and then the seventh

note is of medium length; in the 9-grunt the first five notes are very rapid and short, then

the sixth, seventh, and eighth notes are a triple, and then the ninth note is long. No grunts

of 8 beats could be documented in this study, although further analysis of the recordings

is needed to confirm this. Two other of the calls given by the silverback Matt sound

exactly like those rhythms you hear in jazz music. Specifically, the inverted double

grunt, is heard in the tenor saxophone solo of “You Put a Spell on Me” as sung by Nina

Simone and the trill of the tenor saxophone sounds exactly like the chutter of the gorillas.

In addition, the quadruple grunt can be heard in this trumpet solo. These basic rhythms

are also heard in homeric epics in which the last five syllables had to be of a particular

rhythm: long, short, short, long, short (Halporn, et al., 1994). If you replace the first

triple note of the 7-grunt with a long note or syllable, then the 7-grunt is like the last 5

syllables of Homeric epics. Are these basic rhythmic phrases shared with gorillas and

our last common ancestor? Why are these rhythmic grunts heard in this captive gorilla

and not in wild gorillas? This gorilla, Matt, was hand reared from the age of 3 months to

11 months so it is not unreasonable to think that he had exposure to human music as in

infant which he then produced as an adult. In addition, many keepers play music while

they are cleaning the gorillas’ enclosures, so it is not unreasonable to think that Matt

could have also picked up these musical phrases through that exposure as an infant,

juvenile or an adult.

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Future Directions:

More detailed vocal communication and personality data, using 54 descriptive

adjectives, from more populations of captive and wild gorillas are needed to test if

personality does explain behavior and individual vocal patterns. Perhaps more accurate

data could be collected with many focused studies on specific captive populations instead

of multi-institutional studies with as many as thirty-seven different people collecting data

on twenty-five gorillas (Kuhar, et al., 2004). Also, published comparative data on

bonobos would allow us to complete the story for the emergence of conscientiousness in

our common ancestors with the great apes. Lastly, another avenue for future study is to

determine if personality impacts reproductive success in silverbacks. Was a high

conscientiousness score a trait preferred by female gorillas for it to evolve in the ancestor

of gorillas and not orangutans?

The origin of the quadruple grunt and multiple grunt could be traced through the

blood relatives and cage-mates of Matt, the only gorilla known at this time to give

rhythmic multiple grunts. With these additional data we can determine whether giving

these calls is a learned, cultural phenomenon, or whether they are a more innate behavior

found in both wild and captive populations of gorillas. Documenting the vocal profiles of

individual gorillas would provide us with insight into the development of gorilla

vocalizations and answer whether they are only GOPs, or groans of pain, (Griffin, 1992)

or something more complex. We could then answer the question of whether gorilla

vocalizations are innate or learned. We could also answer the question of whether the

capacity for rhythm is innate or if culture is needed to bring it out. The origins of music

and language in the form of a singing stage in human evolution could be found to be

85

more ancient that previously thought (Mithen, 2006; Dunbar, 2004; Merker, 2000;

Richman, 2000; Richman, 1993; Livingstone, 1973).

86

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Curriculum Vitae

Sarah Ann Schaefer

Education

2011 Ph.D. in Anthropology, Rutgers University, New Brunswick, NJ

2007 M.A. in Anthropology, Rutgers University, New Brunswick, NJ

2003 M.S. in Anthropology, Purdue University, West Lafayette, IN

1991 B.A. in Anthropology, Mount Holyoke College, South Hadley, MA

Employment

2005-2009 Teaching Assistant, Rutgers University, New Brunswick, NJ

2000-2002 Teaching Assistant, Purdue University, West Lafayette, IN

Publications

2003 The Impact of Seasonality, Inter-Annual Variability, and Selective

Logging on Gorilla Food Availability at Bai Hokou, Central African

Republic. M.S. thesis, Purdue University.