THE EFFECTS OF HUMAN CROWDS ON CHIMPANZEES
Esther Verbruggen
David Douglas High School, 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 stressed 1. In times when
rhesus monkeys (a type of primate) are more crowded, grooming increases, possibly to relieve
tensions and stress 2.
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 people 3. 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.
Primetime Primates Scientific American Frontiers 1995
3
(2009). Zoo chimp 'planned' stone attacks. BBC News.
2
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 Ethogram 4
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, Filippo and Judge, Peter G. (2000). Coping With Crowding.
Scientific American; pg. 76-81.
Goodall, Jane (1986). The Chimpanzees of Gombe: Patterns of Behavior. The Belknap Press of
Harvard University Press.
Landau, Virginia (1997). Learning about Nonhuman Primates. ChimpanZoo, The Jane Goodall
Institute.
Doviak, Steven (2008). Query Count. ChimpanZoo Database System. The Jane Goodall Institute.