This article was downloaded by: [Dr Kenneth Shapiro]On: 09 June 2015, At: 08:58Publisher: RoutledgeInforma Ltd Registered in England and Wales Registered Number: 1072954Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH,UK

Journal of Applied AnimalWelfare SciencePublication details, including instructions forauthors and subscription information:http://www.tandfonline.com/loi/haaw20

Behavioral Responses ofSilverback Gorillas (Gorillagorilla gorilla) to VideosMargaret A. Maloney a , Katherine A. Leighty a ,Christopher W. Kuhar b & Tamara L. Bettinger aa Disney's Animal Kingdom® , Lake Buena Vista,Floridab Cleveland Metroparks Zoo , Cleveland, OhioPublished online: 26 Mar 2011.

To cite this article: Margaret A. Maloney , Katherine A. Leighty , Christopher W.Kuhar & Tamara L. Bettinger (2011) Behavioral Responses of Silverback Gorillas(Gorilla gorilla gorilla) to Videos, Journal of Applied Animal Welfare Science, 14:2,96-108, DOI: 10.1080/10888705.2011.551621

To link to this article: http://dx.doi.org/10.1080/10888705.2011.551621

PLEASE SCROLL DOWN FOR ARTICLE

Taylor & Francis makes every effort to ensure the accuracy of all theinformation (the “Content”) contained in the publications on our platform.However, Taylor & Francis, our agents, and our licensors make norepresentations or warranties whatsoever as to the accuracy, completeness,or suitability for any purpose of the Content. Any opinions and viewsexpressed in this publication are the opinions and views of the authors, andare not the views of or endorsed by Taylor & Francis. The accuracy of theContent should not be relied upon and should be independently verified withprimary sources of information. Taylor and Francis shall not be liable for anylosses, actions, claims, proceedings, demands, costs, expenses, damages,and other liabilities whatsoever or howsoever caused arising directly or

indirectly in connection with, in relation to or arising out of the use of theContent.

This article may be used for research, teaching, and private study purposes.Any substantial or systematic reproduction, redistribution, reselling, loan,sub-licensing, systematic supply, or distribution in any form to anyone isexpressly forbidden. Terms & Conditions of access and use can be found athttp://www.tandfonline.com/page/terms-and-conditions

Dow

nloa

ded

by [

Dr

Ken

neth

Sha

piro

] at

08:

58 0

9 Ju

ne 2

015

JOURNAL OF APPLIED ANIMAL WELFARE SCIENCE, 14:96–108, 2011

Copyright © The Walt Disney Company®

ISSN: 1088-8705 print/1532-7604 online

DOI: 10.1080/10888705.2011.551621

Behavioral Responses of SilverbackGorillas (Gorilla gorilla gorilla)

to Videos

Margaret A. Maloney,1 Katherine A. Leighty,1

Christopher W. Kuhar,2 and Tamara L. Bettinger1

1Disney’s Animal Kingdom®, Lake Buena Vista, Florida2Cleveland Metroparks Zoo, Cleveland, Ohio

This study examined the impact of video presentations on the behavior of 4 silver-

back, western lowland gorillas (Gorilla gorilla gorilla). On each of 5 occasions,

gorillas viewed 6 types of videos (blue screen, humans, an all-male or mixed-

sex group engaged in low activity, and an all-male or mixed-sex group engaged

in agonistic behavior). The study recorded behavioral responses and watching

rates. All gorillas preferred dynamic over static videos; 3 watched videos depicting

gorillas significantly more than those depicting humans. Among the gorilla videos,

the gorillas clearly preferred watching the mixed-sex group engaged in agonistic

behavior; yet, this did not lead to an increase in aggression or behavior indicating

agitation. Further, habituation to videos depicting gorillas did not occur. This

supports the effectiveness of this form of enrichment, particularly for a nonhuman

animal needing to be separated temporarily due to illness, shipment quarantine,

social restructuring, or exhibit modification.

A wide variety of enrichment activities have been used to stimulate nonhuman

animals both physically and psychologically in research laboratories, zoos, and

sanctuaries (McCann et al., 2007). These activities historically include climbing

devices such as perches and objects the animals can manipulate such as toys,

puzzle-feeders, and varying edibles. More recently, the use of videos as enrich-

ment or operant rewards has been evaluated for a variety of nonhuman primate

Correspondence should be sent to Katherine A. Leighty, Disney’s Animal Kingdom®, P.O. Box

10,000, Lake Buena Vista, FL 32830. Email: Katherine.Leighty@Disney.com

96

Dow

nloa

ded

by [

Dr

Ken

neth

Sha

piro

] at

08:

58 0

9 Ju

ne 2

015

SILVERBACK GORILLA REACTIONS TO VIDEOS 97

species living in different captive conditions (Bloomsmith, Keeling, & Lambeth,

1990; Lutz & Novak 2005; Morimura, 2006). For enrichment techniques to be

effective, they must encourage species-appropriate behavior as well as provide

the animals with opportunities to make choices or otherwise exert control over

their environment (Mellen & MacPhee, 2001). Given that primates as an order

are highly visually oriented (Napier & Napier, 1985), video presentations can

potentially stimulate their innate observing responses while also allowing them

to control their exposure to video content by either turning away or relocating

to a different area of their environment.

Interest in video stimuli has been observed in several monkey species. For

example, Andrews and Rosenblum (1993) found that color video images were

as effective as banana pellets to reinforce bonnet macaques (Macaca radiata)

working on joystick tasks. Further, Platt and Novak (1997) found when video was

presented for enrichment purposes, rhesus monkeys (Macaca mulatta) watched

the monitor 25% of the time and demonstrated an overall increase in activ-

ity level. Butler (1961) discovered that the content and quality of the image

presented to the animal affects visual attention; specifically, rhesus macaques

were found to watch dynamic images preferentially over static ones and images

that were in focus rather than blurred. Further, both pigtail macaques (Macaca

nemestrina) and bonnet macaques have been observed to give socially appro-

priate responses to videos depicting threatening and nonthreatening conspecifics

(Capitanio, Boccia, & Colaiannia, 1985; Plimpton, Swartz, & Rosenblum, 1981).

Given this documented interest in video stimuli, it has been recommended

as a method of enrichment for a variety of nonhuman primate species (Lutz &

Novak, 2005; Morimura, 2006). In a study of the effectiveness and behavioral

implications of presenting video to chimpanzees in captivity (Pan troglodytes),

Bloomsmith and colleagues displayed videos of varied content including other

chimpanzees, other animals, their human caretakers, television programs, or a

blank screen as a control (Bloomsmith et al., 1990). The chimpanzees were

found to watch videos of humans and chimpanzees significantly more than the

static control, and they attended to the monitor 42% of the time during the

dynamic videos. More specifically, all subjects preferred videos of chimpanzees

engaged in agonistic behaviors (chasing, threatening, contact aggression) over

all other behavior categories including feeding, playing, and grooming. The

subjects did demonstrate some degree of habituation to the videos with repeated

presentations; however, their watching rate remained substantial.

Other than visually attending to these videos, analyses revealed no signifi-

cant deviations from subjects’ typical daily behavioral repertoire during video

presentation (Bloomsmith & Lambeth, 2000). Brent and Stone (1996) further

demonstrated the utility of televised images as an enrichment technique. They

found that a television was the most frequently utilized device by chimpanzees

when presented with an array of enrichment items over a prolonged period.

Dow

nloa

ded

by [

Dr

Ken

neth

Sha

piro

] at

08:

58 0

9 Ju

ne 2

015

98 MALONEY, LEIGHTY, KUHAR, BETTINGER

Less has been documented about the potential value of video as enrichment

for gorillas, but Maple and Hoff (1982) did present western lowland gorillas

(Gorilla gorilla gorilla) at the Sacramento Zoo with a 16-mm film depicting

gorillas copulating in an attempt to stimulate breeding. Their objective was not

achieved; however, the gorillas did attend to the video. The silverback responded

to specific content including loud noises. Building from these observations, one

aim of the present study was to determine the effectiveness of video presentation

as a form of enrichment for silverback gorillas.

For more than 10 years, Disney’s Animal Kingdom® has maintained two

social groupings of western lowland gorillas: a mixed-sex troop currently con-

sisting of one silverback and three adult females and an all-male troop of four

adult silverback males. During the day, these two social groups are housed

in separate naturalistic outdoor habitats (1765.16 m2 and 2601.29 m2) that

face each other. This allows visual, olfactory, and auditory access between

groups. Previous research has suggested that exhibit designs such as this may

affect the dynamics of all-male groups by increasing noncontact aggression

(Stoinski, Kuhar, Lukas, & Maple, 2004). Therefore, a second focus of this

study was to determine whether the silverbacks of the all-male troop would

respond differently to video of the mixed-sex troop compared with their own.

Modeling the work of Bloomsmith et al. (1990), we presented these animals

with an array of videos and documented their attention and other behavioral

responses.

METHOD

Subjects and Housing

Four silverback western lowland gorillas at Disney’s Animal Kingdom®, ages

15 to 27 years, served as subjects for this study (see Table 1). Testing sessions

were conducted in the mornings while the gorillas were individually housed in

their overnight sleeping quarters. These holding areas vary in size from 51 to

76.5 m3 and have front panels made of 5 � 5 cm galvanized mesh. Each area

TABLE 1

Gorilla Demographics

Name Age at Start of Study Relevant Rearing History

G 27 Hand reared in absence of gorillas

K 17 Mother reared

Z 17 Mixed rearing

S 15 Mixed rearing

Dow

nloa

ded

by [

Dr

Ken

neth

Sha

piro

] at

08:

58 0

9 Ju

ne 2

015

SILVERBACK GORILLA REACTIONS TO VIDEOS 99

contains a skylight to let in fresh air with a galvanized mesh barrier from which

enrichment items are attached to encourage climbing and foraging behaviors.

Situated throughout the room are benches of varying heights and stainless steel

platforms that provide elevated resting areas and locations on which the gorillas

can build nests from bedding materials. Prior to each session the gorillas were

fed their normal morning portion of primate chow. At the completion of data

collection and the remainder of the morning’s husbandry routine, all subjects

were given access to their shared outdoor naturalistic yard.

Materials

A cart containing a 21-in. (53.3-cm) color television (Sony Trinitron) was

wheeled in front of the gorilla and one of six 10-min videos was played (Table 2).

All videos were played without sound to control for this potential confound. Each

10-min gorilla video showed a collection of short video clips edited together of

either the all-male group or the mixed-sex group at Disney’s Animal Kingdom®.

For each of the four gorilla videos, each member of the group depicted was

presented on screen for equal amounts of time to control for differential response

to specific individuals. Behavioral observations of the gorillas were conducted

using the Observer® XT (Noldus, Leesburg, VA) program on an iPAQ (Hewlett-

Packard, #HX2495B, Palo Alto, CA).

Procedure

To allow for acclimation, the gorillas were introduced to the cart, television,

and human observer several times before the study began. Testing sessions were

conducted 5 days per week from September through December 2008 between

TABLE 2

Video Types and Content

Videos Description

Blue screen Control video

Humans Depicting park guests

All-male group, low activity Members of the all-male troop exhibiting behaviors such

as eating, walking, and being inactive

Mixed-sex group, low activity Members of the mixed-sex troop exhibiting behaviors such

as eating, walking, and being inactive

All-male group, agonistic Members of the all-male troop exhibiting behaviors such

as chest beating, standing in a stiff stance, and chasing

Mixed-sex group, agonistic Members of the mixed-sex troop exhibiting behaviors such

as chest beating, standing in a stiff stance, and chasing

Dow

nloa

ded

by [

Dr

Ken

neth

Sha

piro

] at

08:

58 0

9 Ju

ne 2

015

100 MALONEY, LEIGHTY, KUHAR, BETTINGER

TABLE 3

Ethogram Used During Gorilla Observations

Behaviors Definition

Charge Run in a swift and aggressive manner

Chest beating Rapid striking of the chest/abdomen using the hands

Eat/Forage Consume or search for food, drink water

Flee Rapid distancing from monitor

Locomote Movement from one area to another by walking

Pacing Repetitive locomotion occurring at least two times in a row

Play Use of enrichment device in enclosure

Pursed lips Puffed out upper and lower lip areas

Self-groom Visually inspect, lick, or scratch own body

Slap/Bang Body contacts part of the enclosure aggressively

Stiff stance Rigid body with forearms stiff and close together, hands formed tightly

with fingers curled in, standing on knuckles

Throw object Launch object into the air

Undesirable Coprophagy, regurgitate and reingest

Vocalize Emit audible vocal sound

Watching Gaze is directed at the monitor

Not visible behavior Gorilla is out of the observer’s view

Other Behavior observed is not defined in the ethogram

the hours of 0730 and 0800. Each morning, 2 of the 4 gorillas were randomly

selected to participate one at a time in the study. The order of video presentation

was randomized such that each gorilla viewed each of the six videos on five

separate occasions, resulting in 30 testing sessions with each gorilla. During all

of the sessions, the observer stood out of direct view of the gorillas and did not

interact with them at any point. While the video played, the observer recorded

the frequency and duration of behavioral responses (Table 3).

Analyses

To examine all behaviors exhibited during video presentation (with the exception

of “watching”), the time spent engaged in each behavior was calculated as

a proportion of the time the animal was visible to the observer. The time

spent “watching” the video was calculated as a proportion of the 10-min video

duration. The mean of these values was calculated for each subject for each of

the six video types.

A dependent t test was used to determine if subjects differed in the pro-

portion of time spent (a) watching dynamic videos (all video types except

the blue screen) compared with the static ones (blue screen) and (b) watching

videos depicting gorillas (four gorilla videos) compared with humans. For these

Dow

nloa

ded

by [

Dr

Ken

neth

Sha

piro

] at

08:

58 0

9 Ju

ne 2

015

SILVERBACK GORILLA REACTIONS TO VIDEOS 101

analyses, the parametric test was selected because it is not possible to obtain

a significant result with the corresponding nonparametric test given that only

4 subjects contributed data (lowest possible p value with 4 subjects is .068

for this test). This fact will be considered when drawing conclusions from this

data. A 2 � 2 Factorial ANOVA was used to examine the impact of social

group depicted (all-male vs. mixed-sex) and behavioral content (low activity vs.

agonistic) on time spent watching gorilla videos.

To control for individual differences in overall video-watching time in this

analysis, the z score of each individual’s mean proportion of video watching for

each video type was used in the analysis. This transformation had the additional

outcome of increasing normality within the data set. Visual inspection of the

time spent watching videos over repeated presentations was used to determine

whether habituation took place. All statistical tests were two-tailed with alpha

set at 0.05 and conducted with SPSS 15.0 (Chicago, IL).

Activity During Video Presentation

The proportion of time engaged in each behavior category during video presen-

tation is displayed in Figure 1. Of all behaviors, subjects spent the most time

FIGURE 1 Proportion of time each gorilla spent engaged in the recorded behaviors when

shown the static blue screen, human, and gorilla videos.

Dow

nloa

ded

by [

Dr

Ken

neth

Sha

piro

] at

08:

58 0

9 Ju

ne 2

015

102 MALONEY, LEIGHTY, KUHAR, BETTINGER

watching the television monitor, with the exception of the blue-screen control

condition in which subjects spent less time watching the monitor than they did

eating/foraging. For ease of presentation, all behaviors in the ethogram reflecting

agonistic or agitated responses to the videos were grouped into a single category

entitled “agonistic/agitation.” The category included charge, chest beating, flee,

pacing, pursed lips, slap/bang, stiff stance, and throw object. These behaviors

were not demonstrated at a substantial rate to any of the video types. Visual

inspection of the behavioral data revealed that no behaviors were remarkably

altered between the static video control condition and the videos depicting human

or gorilla content with the exception of the degree to which the video was

watched by the subject.

Watching of Static Versus Dynamic Videos

The mean proportion of the video watched for the static blue-screen control video

ranged from 0.008 (S) to 0.172 (G) with a mean across subjects of 0.060 ˙

.038. For the dynamic videos, subjects ranged from 0.296 (G) to 0.711 (S) with

a mean proportion of the video watched of 0.547 ˙ .089. Thus, the subjects

spent significantly more time watching videos containing dynamic images than

the static blue control screen (t (3) D �3.859, p D .031; see Figure 2).

FIGURE 2 Proportion of time each gorilla was visible to the observer that was spent

watching the static and dynamic videos.

Dow

nloa

ded

by [

Dr

Ken

neth

Sha

piro

] at

08:

58 0

9 Ju

ne 2

015

SILVERBACK GORILLA REACTIONS TO VIDEOS 103

RESULTS

Watching of Human Versus Gorilla Videos

When shown the video depicting humans, the mean proportion of the video

watched ranged across subjects from 0.339 (G) to 0.504 (S) with a mean of

0.405 ˙ .035. For the videos depicting gorillas, subjects ranged from 0.286 (G)

to 0.763 (S) with a mean proportion of the video spent watching of 0.583 ˙ .104.

When analyzing across all subjects, the proportion of the video watched was

not significantly different across the human and gorilla videos (t (3) D �2.234,

p D .122); yet, 3 of the 4 subjects did watch significantly more of the gorilla

videos than the human video (t (2) D �8.710, p D .013; see Figure 3).

Impact of Gorilla Video Content on Watching Rate

To examine the impact of the behavioral content and social group depicted

on the gorilla videos, the mean proportion of the video watched was cal-

culated for each subject for each of the four gorilla-video types. A 2 � 2

Factorial ANOVA (gorilla social group by behavioral content) of the z scores

of these values revealed a significant main effect for gorilla social group de-

FIGURE 3 Proportion of time each gorilla was visible to the observer that was spent

watching the human and gorilla videos.

Dow

nloa

ded

by [

Dr

Ken

neth

Sha

piro

] at

08:

58 0

9 Ju

ne 2

015

104 MALONEY, LEIGHTY, KUHAR, BETTINGER

FIGURE 4 Proportion of time all gorillas spent watching the video as a function of social

group depicted (all-male or mixed-sex) and behavioral content (low activity or agonistic).

picted (F(1) D 4.916, p D .047) with the subjects watching videos of the

family group (nontransformed M D 0.623, SE D 0.090) over those of the

bachelor group (nontransformed M D 0.543, SE D .077). A significant main

effect was also present for the behavioral content of the gorilla videos (F(1)

D 21.582, p D .001) with the subjects watching videos of agonistic behavior

(nontransformed M D 0.673, SE D 0.092) over those depicting low-activity

behavior (nontransformed M D 0.492, SE D 0.061). A significant interaction

was present between social group depicted and behavioral content (F(1) D

6.626, p D .024) with the video depicting the family group engaged in agonistic

behavior to be the most attended to (nontransformed M D 0.757, SE D 0.138;

see Figure 4).

Habituation to Videos

Visual inspection of the time spent watching the videos over repeated presen-

tations revealed marked habituation to the human videos over time, such that

there was a 74% decrease in time spent watching between the first and fifth

presentation of the human video. Habituation was not evident in the subjects’

watching of gorilla videos (Figure 5).

Dow

nloa

ded

by [

Dr

Ken

neth

Sha

piro

] at

08:

58 0

9 Ju

ne 2

015

SILVERBACK GORILLA REACTIONS TO VIDEOS 105

FIGURE 5 Mean number of seconds all gorillas spent watching the 10-min human and

gorilla videos across five presentations.

DISCUSSION

As seen in other primate species, these silverback gorillas demonstrated a high

level of interest in video presentations. This novel change to their environment

appeared to be engaging for these animals as they spent a large proportion of

their time visually focused on the video. Dynamic videos displaying human and

gorilla content resulted in significantly higher watching rates compared with

the static blue-screen control video, demonstrating that the gorillas were clearly

attending to the content of the videos (Figure 2). This preference for dynamic

images reinforces similar findings in chimpanzees (Bloomsmith et al., 1990) and

rhesus macaques (Butler, 1961).

The species depicted in the dynamic videos also had a significant impact

on the engagement of the gorillas. Three of the 4 subjects had a significant

preference for watching videos of gorillas over humans (Figure 3). This may in-

dicate the potential for gorillas to selectively attend to their own species. Similar

selective attention within species has been seen in facial recognition processing

of both humans and nonhuman primates (Neiworth, Hassett, & Sylvester, 2007;

Dow

nloa

ded

by [

Dr

Ken

neth

Sha

piro

] at

08:

58 0

9 Ju

ne 2

015

106 MALONEY, LEIGHTY, KUHAR, BETTINGER

Pascalis & Bachevalier, 1988). It is interesting that the 1 animal in this study who

did not prefer the gorilla videos, G, has a rearing history unique from the other

subjects (Table 1). G was rejected by his mother soon after birth and required

hand rearing. Because of husbandry demands, this hand rearing was conducted

out of visual contact with other gorillas. Thus, his response to these videos may

reflect his early exposure to humans and lack of early experience to gorillas.

Further, G was also the oldest of the 4 subjects in this study, and his watching

rates across all video types were lower than those of the other animals. On the

other hand, S, the youngest animal observed, had the highest watching rates.

This may suggest a negative relationship between age and attention to videos,

with older animals having a reduced attention span to this form of media. Further

investigation, including a larger sample of animals from a variety of facilities,

will be needed to tease out the impacts of age and early rearing history on

interest in video stimuli in nonhuman primates.

Among the videos depicting gorillas, analyses revealed a significant inter-

action between social group depicted and behavioral content of the video on

the time spent watching. That is, subjects showed a significant preference for

watching gorillas engaged in agonistic behaviors such as chest beating and

charging, particularly when it involved the mixed-sex troop housed in the facing

enclosure (Figure 4). Although this video type did cause more engagement

with the video, it did not lead to the production of agonistic behaviors or

behaviors reflecting agitation, such as fleeing or pacing during the observation

period (Figure 1). Thus, it appears that the subjects recognize alteration in

behavioral and social content; however, they do not respond to it in any way other

than adjusting their level of visual attention. Recent studies with chimpanzees

have shown that they are able to comprehend the representational relationship

between 2D video images and the 3D world without confusing the two (Leighty,

Menzel, & Fragaszy, 2008; Menzel, 2005). That is, they do not react to video

presentations as if they were actual 3D events; rather, they are able to use them

as a tool to gain information about their 3D environment such as the location

of a hidden food item. It is likely the case here that the gorillas comprehend

that the images they are viewing on the 2D monitor are only representations

of real-world events and that they are not actually occurring in the present

time.

There was no apparent decline in the subject’s watching rates to the four

gorilla videos with repeated presentation. Thus, there was no evidence of these

subjects habituating to the content of these videos over five viewings. On the

other hand, a clear habituation effect was seen to the video depicting humans,

with a particularly sharp decline following the third presentation (Figure 5).

Taken together, these findings reiterate the notion that these animals are stimu-

lated by watching video of their own species. We therefore conclude that video

depicting gorilla behavior is a valuable and cost-effective enrichment tool that

Dow

nloa

ded

by [

Dr

Ken

neth

Sha

piro

] at

08:

58 0

9 Ju

ne 2

015

SILVERBACK GORILLA REACTIONS TO VIDEOS 107

promotes positive welfare. We feel it would be particularly useful in cases when

animals must be temporarily separated due to illness, shipment quarantine, social

restructuring, and/or exhibit modification, and can be a useful component of a

comprehensive enrichment program.

ACKNOWLEDGMENTS

This research would not have been possible without the support and assistance

of the keepers and managers of the Primate Husbandry Team at Disney’s Animal

Kingdom®. We thank James Gash for his assistance with video editing.

REFERENCES

Andrews, M. W., & Rosenblum, L. A. (1993). Live-social video reward maintains joystick task

performance in bonnet macaques. Perceptual and Motor Skills, 77, 755–763.

Bloomsmith, M. A., Keeling, M. E., & Lambeth, S. P (1990). Videotapes: Environmental enrichment

for singly housed chimpanzees. Lab Animal, 19, 42–46.

Bloomsmith, M. A., & Lambeth, S. P. (2000). Videotapes as enrichment for captive chimpanzees.

Zoo Biology, 19, 541–551.

Brent, L., & Stone, A. M. (1996). Long-term use of televisions, balls, and mirrors as enrichment

for paired and singly caged chimpanzees. American Journal of Primatology, 39, 139–145.

Butler, R. A. (1961). The responsiveness of rhesus monkeys to motion pictures. The Journal of

Genetic Psychology, 98, 239–245.

Capitanio, J. P., Boccia, M. L., & Colaiannia, D. J. (1985). The influence of rank on affect perception

by pigtailed macaques (Macaca nemestrina). The American Journal of Primatology, 8, 53–59.

Leighty, K. A., Menzel, C. R., & Fragaszy, D. M. (2008). How young children and chimpanzees (Pan

troglodytes) perceive objects in a 2D display: Putting an assumption to the test. Developmental

Science, 11, 778–792.

Lutz, C. K., & Novak, M. A. (2005). Environmental enrichment for nonhuman primates: Theory

and application. Institute for Laboratory Animal Research, 46, 178–191.

Maple, T. L., & Hoff, M. P. (1982). Gorilla behavior. New York, NY: Van Nostrand Reinhold.

McCann, C., Buchanan-Smith, H., Jones-Engel, L., Farmer, K., Prescott, M., Fitch-Snyder, H., &

Taylor, S. (2007). IPS international guidelines for the acquisition, care, and breeding of nonhu-

man primates. International Primatological Society, Second Edition. Retrieved from http://www.

internationalprimatologicalsociety.org/docs/IPS_International_Guidelines_for_the_Acquisition_

Care_and_Breeding_of_Nonhuman_Primates_Second_Edition_2007.pdf

Mellen, J., & MacPhee, M. S. (2001). Philosophy of environmental enrichment: Past, present, and

future. Zoo Biology, 20, 211–226.

Menzel, C. R. (2005). Progress in the study of chimpanzee recall and episodic memory. In H.

Terrace & J. Metcalfe (Eds.), The missing link in cognition: Origins of self-reflective consciousness

(pp. 188–224). New York, NY: Oxford University Press.

Morimura, N. (2006). Cognitive enrichment in chimpanzees: An approach of welfare entailing

an animal’s entire resources. In T. Matsuzawa, M. Tomonaga, & M. Tanaka (Eds.), Cognitive

development in chimpanzees, (pp. 368–391). Tokyo, Japan: Springer-Verlag.

Napier, J. R. & Napier, P. H. (1985). The natural history of primates. Cambridge, MA: MIT Press.

Dow

nloa

ded

by [

Dr

Ken

neth

Sha

piro

] at

08:

58 0

9 Ju

ne 2

015

108 MALONEY, LEIGHTY, KUHAR, BETTINGER

Neiworth, J. J., Hassett, J. M., & Sylvester, C. J. (2007). Face processing in humans and new world

monkeys: The influence of experimental and ecological factors. Animal Cognition, 10, 125–134.

Pascalis, O., & Bachevalier, J. (1988). Face recognition in primates: A cross-species study. Be-

havioural Processes, 43, 87–96.

Platt, D. M., & Novak, M. A. (1997). Video stimulation as enrichment for captive rhesus monkeys

(Macaca mulatto). Applied Animal Behaviour Science, 52, 139–155.

Plimpton, E. H., Swartz, K. B., & Rosenblum, L. A. (1981). Responses of juvenile bonnet macaques

to social stimuli presented through color videotapes. Developmental Psychobiology, 14, 109–115.

Stoinski, T. S., Kuhar, C. W., Lukas, K. E., & Maple, T. L. (2004). Social dynamics of captive

western lowland gorillas living in all-male groups. Behaviour, 141, 169–195.

Dow

nloa

ded

by [

Dr

Ken

neth

Sha

piro

] at

08:

58 0

9 Ju

ne 2

015