THE EFFECTS OF HUMAN CROWDS ON CHIMPANZEES

Esther Verbruggen

Portland, Oregon

ABSTRACT

This study observes the changes in chimpanzee behavior between small and large crowds. Three

contexts, (bad observations, public orientation and solitary) were observed of five chimps. Three

behaviors (grooming, food, and idle) were also observed. Results indicate that larger crowds

increase idle behavior and decrease grooming and food behaviors.

INTRODUCTION

Imagine you're walking down the street, and you see a couple of people staring at you. One even

points and laughs. Now imagine you turn the corner, and there is a whole crowd, watching your

every move, some pointing fingers, others making comments and laughing. How would your

behavior change from a few people to many people? Chimpanzees living in zoos are constantly

being observed by a variety of human strangers; young children, the elderly, adults, teenagers.

However, sometimes there are more humans watching than at other times. How do you suppose

the chimpanzees’ behavior changes from small to large crowds?

Chimpanzees in zoos are often subjected to crowded spacing and noisy neighbors. When

neighboring chimps are being loud, chimpanzees tend to become more stressed1. In times when

rhesus monkeys (a type of primate) are more crowded, grooming increases, possibly to relieve

tensions and stress2.

Neighboring chimpanzees aren't the only noisy neighbors chimps have to deal with. They have

another noisy neighbor: humans. Every day, the chimpanzees are subject to humans staring,

yelling, laughing, and pointing. Not only are these neighbors noisy, they are also interfering with

the chimps' privacy. In one Swedish zoo, a chimpanzee became so fed up with the human crowds

that he began a ritual of throwing rocks at people3. Human crowds are an element of everyday

life for chimpanzees.

Questions:

Are chimpanzees affected by human crowds? If so, how do human crowds affect chimpanzee

behaviors, such as grooming, food and idle behavior? How are context such as public

orientation, bad observations and solitary affected?

1 de Waal, F. B. M., Aureli, F., & Judge, P. G. (2000). Coping with crowding. Scientific American 282: 76-81.

2 Primetime Primates Scientific American Frontiers 1995

3 (2009). Zoo chimp 'planned' stone attacks. BBC News.

METHODS

Subjects

The chimpanzees used for this research was a group of geriatric chimpanzees from the Oregon

Zoo. This group consisted of four females and one male. Approximately 240 hours of data were

gathered from the Chimpanzoo Database System, as well as about six hours of individual

observations.

Environments

The chimpanzees all come from the Oregon Zoo. They have continuous access to both an indoor

and an outdoor enclosure, which both include viewing areas for the public. The indoor enclosure

is separated into two rooms, both with a thick glass between the chimps and the public. There are

several platforms along the hall where the chimps often rest, and two holding areas off limits to

public viewing. The outdoor area also includes several viewing areas for the public. For the

chimpanzees there are several climbing platforms, a couple of large caves, and empty concrete

moat, and a few grassy areas. There is also a termite mound often filled with pudding or tomato

sauce.

Procedure:

I. Three behavioral categories and three context categories were used for this research: food,

groom, idle, bad observations, public orientation and solitary. The Chimpanzee Ethogram4

defines these behaviors and contexts:

Behaviors

FOOD denote the presence of food in the hand, mouth, or lip. A submenu lists four food

behaviors:

(H) HAND - The chimpanzee is grasping food with its hand(s).

(M) MOUTH - The chimpanzee can be seen with food in its mouth or chewing it.

(B) BOTH - The chimpanzee may hold food in both the hand(s) and mouth. (W) WADGE -

Some parts of the chimpanzee's meal are not swallowed (the skin and seeds of some fruits, leaves

which have been chewed with meat or eggs or pieces of bones, etc.).

Grooming behavior - Grooming serves a social function in chimpanzee society as well as

keeping the body free from dirt and debris. When grooming, a chimp may use both hands,

pushing the hair back with the thumb or index finger of one hand and holding it back while

picking at the exposed skin with the nail of the thumb or index finger of the other. The chimps

can also use one hand, parting the hair in the same way and holding it back with the lower lip.

Flakes of dried skin and debris are scratched loose and then removed either with the lips or

between thumb and finger.

4 Chimpanzoo Observer's guide pgs. 4, 5, 18, 20, 23.

Idle - A chimpanzee sits or reclines with no purposeful activity.

Contexts

(1) Bad Observation - This is not a behavioral context. This code should be entered whenever the

observer is unable to observe the focal chimpanzee clearly enough to record the chimpanzee's

specific behavior accurately.

(2) Public Orientation Behavior - This context code should be scored when the focal

chimpanzee's attention or visual orientation is clearly directed toward the viewing public,

zookeepers, or other employees.

(7) Solitary-Nonsocial - This context of behaviors applies to situations when an individual or a

mother with her infant positions herself away from the social group and does not interact with

other group members or is clearly inattentive to the social group.

RESULTS

Chimpanzee context cues

Figure 1.

Figure 1 shows no large difference in the chimp's context behaviors between crowd sizes. There

are, however, some minor changes. As the crowd size increases, bad observations increase. This

could indicate that the chimps were either hiding or constantly moving. The average public

orientation decreased as the crowd got larger, going from 8.4% to 6.7%. However, in two of the

individuals, public orientation increased, indicating that chimps respond differently to crowds.

The first chimp went from 4.7% public orienting in a small crowd to 5.8% public orienting in a

large crowd. The second chimp went from 10.6% in a small crowd to 12.4% in a large crowd.

Another interesting change in behavior was the increased idleness as the crowd grew. This is

possibly an indication of increased irritation.

Chimpanzee behavior codes

Figure 2.

Figure 2 displays how behavior was affected in the chimpanzees. Three behaviors, grooming,

food, and idleness, were observed as crowd size changed. Grooming decreased with all subjects

in the study group as the crowd size increased, with an average decrease of 3%. Grooming is an

important social interaction and relationship building behavior among chimps. Food also

decreased inversely to the crowd size. This could be purely coincidental, due to the time of day

when food is distributed, or it could indicate a serious change in behavior. As the crowd grew,

the chimps became increasingly idle. The average increase of idleness between small and large

crowds was 12.3%. While observing the chimpanzees at the zoo, it was noted that they seemed

less willing to move around in front of large crowds.

CONCLUSION

The results seem to show that larger human crowds cause chimps to become more idle. The

chimps also groom less and feeding behavior decreases. Public orientation also decreased while

bad observations increased. The increase in bad observations could indicate that the chimps are

spending more time in their holdings, choosing to seclude themselves to avoid the publics' eyes.

The decrease in grooming behavior is also significant. Grooming is an important relationship

building/maintaining behavior.

DISCUSSION

Although individual chimpanzees may have their own unique reactions to human crowds, they

generally have fairly consistent reactions. The chimpanzees become more idle, groom less and

observe the public less. It is also possible that younger chimps would react differently, for all the

chimps in the observation group were elderly chimps. However, this research makes it clear that

the chimpanzees are impacted by human crowds.

GOING FURTHER

After finishing this study, we are left with several more questions. Would younger chimpanzees

react differently to crowd sizes? Do the crowds impact the chimps' mental health? And what can

be done to reduce the effects of crowds on the chimpanzees?

REFERENCES

De Waal, Frans B. M., Aureli, Filippoand Judge, Peter G. (2000). Coping With Crowding.

Scientific American; pg. 76-81.

Goodall, Jane (1986). The Chimpanzees of Gombe. The Belknap Press of Harvard University

Press.

Landau, Virginia (1997). Learning about Nonhuman Primates. ChimpanZoo, The Jane Goodall

Institute.

DeVorack, Steven (2008). Query Count. ChimpanZoo Database System. The Jane Goodall

Institute.