International Journal of Primatology [ijop] pp758-ijop-460718 March 10, 2003 14:0 Style ﬁle version Nov. 18th, 2002
International Journal of Primatology, Vol. 24, No. 2, April 2003 (
ıve Encounters With Chimpanzees
in the Goualougo Triangle, Republic of Congo
and Crickette Sanz
Received November 5, 2001; revised June 6, 2002
We describe the behavior of an unhabituated population of chimpanzees in the
Goualougo Triangle, Republic of Congo. We encountered chimpanzee parties
on 218 occasions during two ﬁeld seasons (February 1999–December 1999,
June 2000–June 2001). Overall contact rate was 0.63 contacts per day in the
ﬁeld (n = 347). During the ﬁrst 5 min of observation, we recorded individual
responses as curious, ignore, hide, or depart. In contrast to other unhabituated
chimpanzees, curiosity was the most common response (84%) of individuals
in the Goualougo Triangle. However, the responses were deeply integrated
in the group’s reaction to our arrival and behavior throughout an encounter.
Based on the behavior of the majority of individuals in a group, we catego-
rized entire contact events as na
ıve, ignore, nervous, or depart. Na
accounted for 69% of all encounters. Other contacts types occurred much less
frequently: nervous (12%), depart (11%), ignore (8%). Na
ıve contacts were
characterized by chimpanzees that continued to exhibit curiosity throughout
the encounter, the arrival of other individuals at the contact location, and
relatively prolonged contact with observers (average duration: 136 min). It
is likely that the high frequency of curious responses and na
ıve contacts are
due to the remote location of the Goualougo Triangle and the chimpanzees’s
lack of experience with humans. Documentation of this na
has been successfully used to lobby for the protection of the chimpanzees and
KEY WORDS: Pan troglodytes troglodytes; chimpanzee; curious; na¨ıve.
Wildlife Conservation Society, Republic of Congo.
Washington University, St. Louis.
To whom correspondence should be addressed at 1431 Island Dr. S., St. Petersburg, Florida
33707; e-mail: email@example.com.
2003 Plenum Publishing Corporation
International Journal of Primatology [ijop] pp758-ijop-460718 March 10, 2003 14:0 Style ﬁle version Nov. 18th, 2002
370 Morgan and Sanz
With the goal of directly observing the full repertoire of chimpanzee
behavior, researchers at various ﬁeld sites have dedicated many resources
toward achieving habituation: the acceptance by wild animals of a human ob-
server as a neutral elementin their environment (Tutin and Fernandez,1991).
In general, chimpanzees have been difﬁcult to habituate unless provisioned
or patiently followed for several years. As a result, only several chimpanzee
communities have been successfully habituated: Gombe Stream National
Park (Goodall, 1986); Mahale Mountains National Park (Nishida, 1990),
Kibale Forest National Park (Wrangham et al., 1996), Budongo Forest Re-
serve (Reynolds, 1992), Tai National Park (Boesch and Achermann-Boesch,
2000); and Bossou (Sugiyama, 1981). All of them are located in eastern or
western Africa and represent only 2 of the 4 subspecies of chimpanzee: Pan
troglodytes schweinfurthii and Pan troglodytes verus.
Currently, there are no habituated communities of Pan troglodytes
troglodytes, which live in central Africa. Research on the central subspecies
has been limited to surveys of indirect evidence—nests, feeding signs, fe-
ces, tracks—and occasional observations of unidentiﬁed individuals (Fay
and Carroll, 1992; Garcia and Mba, 1997; Gonder et al., 1997; Idani, 1994;
Ihobe, 1993, 1995; Kuroda et al., 1996; Moutsambote et al., 1994; Nishihara,
1995/1996; Tutin and Fernandez, 1984, 1985, 1993a,b; Tutin et al., 1994;
White and Tutin, 2001; Yamagiwa et al., 1995). Attempts have been made
to habituate chimpanzee communities in central Africa by Nishihara (1995/
1996) and Tutin and Fernandez (1991). Tutin and Fernandez (1991) doc-
umented the behavioral responses of chimpanzees to humans in the Lop ´e
Reserve, Gabon. The most common responses were immediate departure by
ﬂight, approach/wait for another before moving away from the observer, and
stealthy retreat. They very rarely exhibited hide, ignore, charge, or curiosity.
Researchers at Guga in the Ndoki Forests of the Republic of Congo suc-
ceeded in directly observating chimpanzees, but a community was never ha-
bituated during their 7-year research presence (Nishihara, 1995/1996). Due
to paucity of data from direct observation of Pan troglodytes troglodytes,
the expansion of mechanized logging, and the effects of rapidly increasing
human populations, it became a priority to identify a site in central Africa
where chimpanzee research was feasible.
In February 1999, a study site was established in the Goualougo Tri-
angle, Republic of Congo. Initial survey teams reported that chimpanzees
there did not immediately ﬂee at the approach of humans, the most common
response of unhabituated chimpanzees (Fay, 1993). Instead of retreating, the
chimpanzees responded to the arrival of human observers with curiosity and
interest. Blake (1995) and Fay (1993) labeled the behavior na¨ıve. It is proba-
bly restricted to individuals with very limited exposure to humans. Due to the
remote location of the Goualougo Triangle, the chimpanzee population and
International Journal of Primatology [ijop] pp758-ijop-460718 March 10, 2003 14:0 Style ﬁle version Nov. 18th, 2002
ıve Encounters With Chimpanzees 371
their habitat have remained undisturbed. The Ndoki and Goualougo Rivers
form the western and eastern borders of the Goualougo Triangle. Their ﬂood-
plains are dominated by swamps that may have formed geographical barriers
to human encroachment. We documented the chimpanzees’s responses to
our presence and its implications for conservation efforts in the region.
STUDY SITE & METHODS
The Goualougo Triangle is located within the Nouabal´e-Ndoki Na-
tional Park (2
E), Republic of Congo (Fig. 1). The
study area covers 30,000 ha of lowland forest and altitudes range between
330 and 600 m. Four habitat types occur in the Goualougo Triangle: mon-
odominant Gilbertiodendron forest, Gilbertiodendron mixed species forest,
mixed species forest, and swamp forest (Fay, 1993, 1997; Kuroda et al., 1996;
Moutsambote, et al., 1994).
The climate is transitional between the Congo-equatorial and subequa-
torial climatic zones (White, 1983). Rainfall is bimodal with a main rainy
season from August through November and a short rainy season in May.
Average monthly rain fall and temperatures at Mbeli Bai base camp, Re-
public of Congo, 17 km from the study area, are 1,710.9 mm (Stokes, 2000)
C (minimum) and 26.5
C (maximum). There is little seasonal vari-
ation it temperature (Stokes, 2000).
Chimpanzee Detection and Contact Protocol
We used 4 methods to locate chimpanzees: mimicking duiker calls to
attract them, hearing their vocalizations or buttress drumming, opportunis-
tic encounters, or conducting vigils of fruiting trees. We most frequently
located chimpanzees by approaching vocalizing groups or by opportunistic
encounters while walking through the forest. Encounters or contact events
involved the direct observation of ≥1 chimpanzee. During all contacts, ob-
servers minimized disturbance to the chimpanzees by immediately sitting
down and remaining quiet. Throughout the contact, chimpanzees dictated
the proximity to the stationary human observers by either moving closer
or retreating. Time of day, environmental conditions, or detection of other
groups occasionally prompted the observers to end contact.
372 Morgan and Sanz
Data Collection Protocols
During the ﬁrst 5 min of observation, we recorded individual responses
as curious, ignore, hide, or depart (Table I). We did not recognize the vo-
calization categories deﬁned by Tutin and Fernandez (1991) as independent
responses, but instead as components of other categories. We collapsed ap-
proach/wait for another, avoid, ﬂight, and stealthy retreat into a single cat-
egory: depart. We observed no change.
Fig. 1. Goualougo Triangle study site.
ıve Encounters With Chimpanzees 373
Table I. Individual response categories (adopted from Tutin and Fernandez, 1991)
Curious Individual response includes ≥2 of the following elements: staring, head
swaying, crouching to get a better view of human observers, moving
closer to observers, slapping tree trunk to elicit response, inquisitive
vocalizations, following observers as they depart.
Ignore No discernable response shown. After noticing an observer, individual
continues with previous activity.
Hide Individual departs from view, but remains at contact location. We
occasionally see individual peering toward us through thick vegetation.
Depart After detecting human observers, individual leaves contact location. This
deﬁnition incorporates all departure categories deﬁned by Tutin and
We categorized entire contacts as na¨ıve, ignore, nervous, or immedi-
ate departure (Table II). Although chimpanzees may have shown different
behaviors, the classiﬁcation is based on the behavior of the majority of
We collected the following data during each contact: method of location;
contact location (forest type, location in canopy or on ground); age-sex class
per Goodall (1986) of all individuals; party size; party type per Doran (1997);
overall contact duration. We identiﬁed individual chimpanzees via detailed
documentation (sketches and video recorded images) of distinctive physical
characteristics (Morgan, 1999). A spotting scope (Bausch and Lomb 15-
45 × 60) aided in viewing the physical features of distant chimpanzees.
Table II. Contact type categories
Na¨ıve After initial response, the majority of chimpanzees present at
a contact show continued curiosity toward human observers
(as indicated by exhibiting curious behaviors: (Table I).
After a period of intense interest, chimpanzees may return
to previous activities while monitoring human observers
(For example, chimpanzee may build a day nest and then
watch human observers while resting).
Ignore Throughout the contact, chimpanzees show no discernible
interest in observers. After noticing arrival of observers,
chimpanzees continue with their previous activities.
Nervous Chimpanzees retreat from observers by moving higher in
canopy or hiding behind vegetation. Chimpanzees alternate
attention between monitoring observers and other
chimpanzees in the party. Other indications of nervousness
include pilo-erection, self-scratching, and loose stool.
Immediate departure All chimpanzees immediately depart after becoming aware of
human presence. Same as depart category for individual
374 Morgan and Sanz
To allow intersite comparisons, we present individual responses in the
same format as Tutin and Fernandez (1991) and Johns (1996). However,
we conducted no statistical analysis on the individual responses because
our study showed that data within each cell were not independent. Based
on repeated contacts of known individuals, individual chimpanzees were
represented more than once in a single cell.
Contact types aptly depicted the behavior exhibited by groups of chim-
panzees in the Goualougo Triangle to the arrival of our research team. Al-
though the same individuals were present at several contacts, we treated
contact events between different groups of chimpanzees on different days
as independent data points. We used Chi-square and Kruskal Wallis tests to
evaluate the relationship between contact categories and other variables.
We collected data during 347 days in 2 ﬁeld seasons (February 1999–
December 1999, June 2000–June 2001). We have total of 365 h of direct obser-
vations during 218 chimpanzee contacts. Overall encounter rate is 0.63 con-
tacts per ﬁeld day. We contacted chimpanzees most frequently by following
vocalizations and buttress drumming to the source (56% of contacts). Other
means of locating chimpanzees include opportunistic encounters (34%), vig-
ils of fruiting trees (8%) and mimicking duiker calls (1.4%).
Initial Responses and Contact Types
The most frequent individual response was curiosity and the most com-
mon contact type was na¨ıve. Table III has the overall relative frequencies
of individual responses by age-sex class. Curious responses were shown by
84% of individuals, and chimpanzees in each age-sex class are represented.
Table III. Individual response to human observers
Adult Subadult Juvenile
Response Male Female Male Female Male Female Infant Unk. Total
Curiosity 266 278 56 38 41 45 177 49 950
Ignore 12 19 2 3 3 1 11 5 56
Hide 9 26 0 3 3 7 24 14 86
Depart 3 5 0 1 1 0 5 24 39
290 328 58 45 48 53 217 92 1131
ıve Encounters With Chimpanzees 375
Table IV. Comparison of individual responses among ﬁeld sites
Lop´e Reserve Kibale Forest Goualougo Triangle
Individual response (n = 153) (n = 436) (n = 1131)
Curiosity 1% 6.70% 84.00%
Ignore 3% 25.80% 4.95%
Hide 5% 6.90% 7.60%
Depart 74% 35.6% 3.45%
Flight 39% 25.50% 1.41%
Stealthy retreat 10% 9.60% 2.03%
Approach/wait for another 25% 0.50% —
Charge 1% 13.10% —
Loud vocalizations 8% 7.10% n/a
Soft vocalizations 8% 4.80% n/a
In Table IV we compare our results with chimpanzee responses in Lop ´e
Reserve (Tutin and Fernandez, 1991) and Kibale Forest (Johns, 1996). In
Goualougo, na¨ıve contacts accounted for 69% of all encounters (Table V).
Other contacts types occurred much less frequently: nervous (11%), depart
(11%), ignore (8%).
Individual Identiﬁcation and Repeated Contacts
We have identiﬁed 152 individual chimpanzees in the Goualougo Tri-
angle study area. The average number of contacts for each individual is 3.63
± 4.04 (range = 1–21). Ninety-eight percent of known individuals have par-
ticipated in ≥1 na¨ıve contact. Some individuals have continued to exhibit
curious behaviors after >20 contacts with human observers.
Table V. Duration of contacts ended by chimpanzees and humans
Proportion of Average
Contact type total contacts duration SD
Chimpanzees end (n = 118)
Na¨ıve 29% 2 hr 16 min 1 hr 38 min
Ignore 6% 2 hr 22 min 2 hr 15 min
Nervous 7% 42 min 37 min
Depart 11% 2 min 1 min
54% 1hr37min 1hr44min
Humans end (n = 100)
Na¨ıve 40% 1 hr 55 min 1 hr 25 min
Ignore 2% 35 min 12 min
Nervous 4% 38 min 40 min
Depart 0 — —
46% 1hr45min 1hr24min
376 Morgan and Sanz
As indicated by contact locations, chimpanzees showed a signiﬁ-
cant preference for certain forest types (χ
= 180.48, df = 2, p < 0.01).
Chimpanzees occurred most often in mixed species forest (76%) and much
less frequently in Gilbertiodendron mixed species forest (14%) and Gilber-
tiodendron forest (10%). We never contacted chimpanzees in swamps. Forest
type is not signiﬁcantly related to contact type (χ
= 0.88, df = 3, NS).
We contacted chimpanzees more often in the canopy (67%) than on
the ground (33%). When contacted on the ground, chimpanzees were twice
as likely to immediately depart than when contacted in the canopy. During
49.5% of all contacts, chimpanzees were observed descending to the ground.
They were most likely to descend to the ground during na¨ıve contacts and
least likely during nervous contacts.
Party Size and Composition
Average initial party size is 3.22 ± 2.07 chimpanzees (n = 218, range =
1 to 14). There is a signiﬁcant difference between party size distributions
among contact types (Kruskal-Wallis, H = 29.21, df = 3, p < 0.01; (Fig. 2)).
Small initial party sizes are associated with immediate departures, and large
initial party sizes are associated with na¨ıve contacts. The small party size
reﬂects the large proportion of lone individuals that immediately departed.
Large party sizes are related to the relatively high proportion of mixed parties
associated with na¨ıve contacts (Fig. 2).
During 74 contacts, party size increased. Most of the increases (95%)
occurred during na¨ıve contacts. For na¨ıve contacts in which party size in-
creased, the average number of new arrivals is 6 ± 4.15 chimpanzees (n =
70, range = 1 to 18). Average total party size for other contact types is sim-
ilar to initial party size. Increases in party size are signiﬁcantly related to
contact type (χ
= 34.40, df = 3, p < 0.01). Table VI shows average initial
party size, number of new arrivals, and total party size among contact types.
The average duration of contacts is 100 ± 95 minutes (n = 218). In
Table V, we compare duration of contacts ended by chimpanzees and hu-
mans by contact type. Duration of contacts ended by chimpanzees is related
to contact type (Kruskal-Wallis, H = 66.64, df = 3, p < 0.01). Depart con-
tacts were brief and showed relatively little variability, range of 1–5 min. In
contrast, na¨ıve and ignore contacts typically lasted >2 h with high variability,
ranging from <10 min to >7h.
ıve Encounters With Chimpanzees 377
Fig. 2. Proportions of different party types by contact type.
Chimpanzees residing in the remote forests of the Goualougo Triangle
most often responded with curiosity to our research presence. Comparing
our data with reports from other sites, showed that the proportion of curious
responses is relatively high (Johns, 1996; Tutin and Fernandez, 1991). How-
ever, researchers conducting initial surveys in remote regions of equatorial
Africa have reported similar encounters with groups of curious primates.
Kortlandt (1962) described encounters with chimpanzees that showed little
Table VI. Relationships between contact type and associated factors
Contact Initial Departure Party size Party size Average
type location location initial (increase) overall duration
Na¨ıve Canopy Descend to ground 3.51 (2.78) 6.29 136 min
Ignore Canopy Remain in canopy 2.78 (0.33) 3.11 142 min
Nervous Ground Remain in canopy 3.32 (0.12) 3.44 42 min
Depart Ground Depart on ground 1.63 (0) 1.63 1 min
378 Morgan and Sanz
fear toward humans in the Democratic Republic of Congo. In Tanzania,
Itani and Suzuki (1967) described encounters with chimpanzees that exhib-
ited curiosity toward their human observers. During a census of primates in
the Ituri Forest, Thomas (1991) found that in remote locations chimpanzees
showed less fear than those that lived in close proximity to humans. They
share a suite of behaviors with chimpanzees in the Goualougo Triangle sug-
gesting that they had limited contact with humans and had not experienced
the negative impacts of human presence, such as hunting, poaching, and
During the past two years of surveys in the Goualougo Triangle, we have
observed that the majority of chimpanzees encountered over a large land-
scape responded to us with curiosity. This phenomenon is more robust than
a few curious individuals; it seemed that the entire population was respond-
ing to a novel stimulus in their environment. This was reinforced by several
instances when the chimpanzees showed curiosity toward other objects. For
example, we observed adult chimpanzees exhibiting curiosity toword unat-
tended backpacks left on the path, tarps, and our empty campsites. During
the past two years, we never encountered other humans or their signs—
cut paths, campsites, trees slashed for rubber—in the Goualougo Triangle.
From the history of the study area, it is likely that our presence constitutes
most of these chimpanzees’s only experiences with humans. This is further
substantiated by their initial responses and continued curiosity.
We also observed that an individual’s reaction was deeply integrated
within a group’s response to our presence. Within contacts, individuals
seemed to be socially referencing from others. If an individual crouched
or moved toward us for a better view, others would also exhibit the behav-
ior. A calm chimpanzee’s relaxed behavior seemed to soothe others, even
if the same individuals showed nervous behaviors in different company. In
contrast, a more fearful individual could easily rouse other chimpanzees with
frequent vocalizations and nervous behaviors. Departures also seemed to be
coordinated as all individuals in a group departed one after another through
the canopy or single-ﬁle on the ground. The reaction of chimpanzee groups
to our presence prompted us to categorize entire contact events as na¨ıve,
ignore, nervous, or depart (Table VI).
Na¨ıve contacts were characterized by curiosity (Table I), the arrival of
other chimpanzees, and maintaining prolonged contact with observers. Dur-
ing na¨ıve contacts, there were many occasions when several individuals in
a group would continue to show curiosity throughout the encounter. They
would move closer, circle around us in the canopy and on the ground, and
remain for hours intently watching us. The excited and inquisitive vocaliza-
tions of chimpanzees initially contacted seemed to draw others to the loca-
tion. New arrivals often vocalized as they approached. Even chimpanzees
ıve Encounters With Chimpanzees 379
that had been contacted several times would join focal groups and monitor
us with interest. On many occasions, we ended na¨ıve contacts with groups
intently watching us depart and sometimes even following us through the
The discovery of a na¨ıve population and their trust in humans is cou-
pled with an obligation to ensure their long-term protection. Similar to ha-
bituated chimpanzees, their lack of fear toward humans could make them
easy victims of poachers. We have also had na¨ıve contacts with other pri-
mate species that would be vulnerable to hunting, including gorillas (Gorilla
gorilla gorilla), grey-cheeked mangabeys (Lophocebus albigena), and-black-
and-white colobus (Colobus guereza). Serving as both a conservation and
research presence in the Goualougo Triangle, we established a study site
and began systematically to document the ecology and behavior of the
chimpanzees. Within a relatively short time, we observed several behaviors
that have been recorded at long-term study sites, including tool use, meat
eating, food sharing, gestural communication, mating, reassurance, groom-
ing, and nesting. We have also begun to elucidate the social structure, ranging
patterns, and feeding ecology of a main study community.
Due to the rapid expansion of commercial timber extraction and in-
creasing human populations, chimpanzee habitats throughout Africa are dis-
appearing at an alarming rate. However, the discovery of na¨ıve chimpanzees
in northern Congo provides hope that intact habitats and populations still
remain. Initial survey teams documented many aspects of the area that are
important to conservation and science, but it was the na¨ıve encounters with
chimpanzee groups that highlighted the Goualougo Triangle as a conserva-
tion priority. Documentation of the chimpanzee’s na¨ıve behavior assisted in
persuading government ofﬁcials and the local logging company to preserve
this pristine habitat. In July 2001, the Goualougo Triangle was annexed to
the Nouabal´e-Ndoki National Park as a result of collaboration between the
Wildlife Conservation Society, the Congolese Ministry of Water and Forests,
and Congolaise Industrielle du Bois. This is an example of how research and
conservation efforts can be combined to identify and pursue the protection
of remaining chimpanzee habitats.
We deeply appreciate the opportunity to work in the Nouabal ´e-Ndoki
National Park and especially the Goualougo Triangle. This has been pos-
sible through the support of the Government of the Republic of Congo
and Wildlife Conservation Society-Congo, with special thanks due to D.
Bourges, B. Curran, and J. M. Fay. Grateful acknowledgment of funding is
380 Morgan and Sanz
due to Columbus Zoological Park, American Zoological Association, and
the Wildlife Conservation Society. In situ facilities and logistical support
have been provided by the Wildlife Conservation Society, Congo. Invalu-
able assistance in the ﬁeld was provided by R. Mokanga, J. P. Koba, and N.
Massembo. Insightful comments on this manuscript and invaluable mentor-
ship during this project were provided by F. Maisels, R. Sussman, P. Lee, T.
Rasmussen, and A. Fuentes. Suggestions made by C. E. G. Tutin and one
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