Pan Africa News, 25(1): 8–10 (2018)

Note

Deposit and Theft? Two Unusual Interactions over Wild Plant
Food between Adult Chimpanzees in Mahale
Takuya Matsumoto1,2,3 & Hiroko Sakuragi1,41 Japan Society for the Promotion of Science (JSPS) Research Fellow
2 Graduate School of Science, Kyoto University, Japan
3 Research Institute for Humanity and Nature, Japan
4 Wildlife Research Center, Kyoto University, Japan(E-mail: matsumoto@chikyu.ac.jp)

INTRODUCTION

using her teeth and placed one half in CT’s right foot. CTkept holding the half with the same foot, while XP kept
the other half in her left hand. CT kept peering at XP’s
mouth and did not show interest in the fragment handedby XP. After XP finished eating the first half, she tookback the half in CT’s foot, all the while CT kept peering at
her. Then, XP divided the retrieved half into quarters andhad CT hold one quarter with his foot again. After finishing her portion, XP took back the quarter from CT’s footand ate it. At 15:55 h, XP put the last piece of fruit in her
mouth while CT continued to peer. XP left the site chewing; CT left 30 s later. Forty seconds after CT moved fromthe site, he obtained a lemon fruit for himself.

Food sharing is assumed to be one of the most important behaviors in the process of human evolution (e.g.,Isaac 1978). Therefore, its occurrence and characteristics
have been studied extensively across primates (McGrew
1975; Jaeggi & van Schaik 2011). Among chimpanzees(Pan troglodytes), the most genetically closest species
to humans (Homo sapiens), food sharing is commonly
observed, and relevant data on several populations havebeen well documented and analyzed (Hosaka 2015).
Food sharing among chimpanzees can often be observed between mothers and infants. Studies suggest that
infants learn food items through food sharing from theirmothers (e.g., Nishida & Turner 1996). Most of the fooditems shared among non-kin adults include meat and cultivated food (Boesch & Boesch 1989; Hockings et al. 2007;
Ohashi 2007). Sharing of wild plant food among adults israre. Boesch & Boesch (1989) defined six types of foodtransfer interactions (focusing on meat) and suggested thatmost are characterized by passive sharing (but see Gilby
2006 for active sharing occurring relatively more often
among Gombe chimpanzees). A recipient shows begging
behavior and takes a part of the food without any facilitation or resistance from the “possessor”, who is defined as
an individual in physical contact with the food (McGrew
1975; Jaeggi & van Schaik 2011).
The present study reports two cases of wild plantfood sharing among chimpanzees. The events are seemingly similar to those reported by Nakamura & Itoh(2001). However, the cases shown here had notable differences from typical food sharing interactions observed inchimpanzees. The subjects were adult chimpanzees (P. t.
schweinfurthii) of the M group at the Mahale Mountains
National Park, Tanzania (see Nakamura et al. (2015) fordetails on the study site and chimpanzee group).

Case 2, on July 19, 2015 (observed by TM and HS)
At 12:37 h, an adult female, BD, was found holding
four fruits of Tabernaemontana pachysiphon (two bunches with two fruits each) on a tree. Another adult female,RJ, rushed to BD and tried to pull the fruits toward herself. BD screamed, apparently resisting; however, RJ succeeded in snatching a bunch. BD started to eat a fruit of
the other bunch while RJ placed the bunch snatched fromBD at her feet. RJ then pulled the fruit that BD was eating
using both hands and started to feed on it (for details of
the event after then, see Video 1 available online at http://mahale.main.jp/PAN/2018/004.html). Both BD and RJ
held the fruit, although only RJ was able to eat it. Aftera while, BD moved slightly away from RJ and the fruits.
After finishing the first fruit, RJ started to eat the second
fruit from the bunch. A while later, BD re-approached,then touched and peered at the fruit that RJ was eating.
RJ seemed to share a small piece once by mouth-to-mouthtransfer. BD tried to pull the fruit toward herself andeat it; however, RJ resisted by biting BD’s arm and face
(Figure 1). RJ started to eat the third fruit, which allowed
BD to have the second’s leftover. However, most edible
portions of the second fruit had been consumed by RJ.
BD peered at the third fruit that RJ was eating, but RJ did
not share. At 12:44 h, BD left the site. RJ continued feeding and ate all four fruits. There were no individuals otherthan BD, RJ and RJ’s infant in the vicinity.

OBSERVATIONS

Case 1, on February 4, 2013 (observed by TM)
At 15:51 h, an adult female, XP, obtained a lemon(Citrus limon) fruit and started to feed. XP placed herright hand on the ground behind her to hold herself up as
she sat cross-legged with her 3-month-old infant sleeping
on her lap. XP peeled the lemon with her left hand andteeth; twenty seconds later, an adult male, CT, approachedand sat beside XP on her left, peering at her mouth. WhenXP finished peeling the lemon, she divided it into halves

DISCUSSION

Although some studies operationally define possession as being in physical contact with the item (McGrew8

Pan Africa News, 25(1): 8–10 (2018)accounted for 31.0% (44 out of 142 captures) of contests
over prey following capture in chimpanzee predation on
mammals during the 1991–1994 period (Hosaka et al.
2001). T. pachysiphon fruits might have been as attractive
to RJ as meat that she snatched it in Case 2.
No data are available on the social rank of BD andRJ. Both immigrated to the M group at the same period in2010 (Hayakawa et al. 2011) and have often traveled in thesame nomadic party. Furthermore, BD has taken care (e.g.,carrying) of RJ’s infant frequently (Sakuragi, unpublisheddata). It is notable that this forceful food transfer occurred
between relatively close individuals.
Previous studies on chimpanzee food sharing havefocused on meat sharing and have found that possessors gain fitness benefits from sharing (e.g., Gilby 2006).
However, the two cases shown in this study reveal thatfood-related interactions in chimpanzees are quite diverse. The first case especially calls for reevaluation of thepossessor–recipient dichotomy regarding food transfer.
It is difficult to reach any general conclusion from thesetwo cases alone; more detailed descriptions and analyses
of interactions related to food transfer are required to elucidate the concept of “possession” of food in chimpanzee
societies.

Figure 1: An adult female, RJ (right), exhibited threateningbehavior toward an adult female, BD (left), which tried totake back the Tabernaemontana pachysiphon fruit.

1975; Jaeggi & van Schaik 2011), Case 1 in the present
study raises a question to this definition. CT kept peering
at the piece of lemon that XP was eating while apparently
showing no interest in the fragment handed by her. XP
took the lemon fruit back from CT’s foot as if from her
own and ate the entire fruit by herself. Both individuals
seemed to share the awareness that the fruit held by CT
belonged to XP, even though the individual in physicalcontact with it was CT, not XP. XP had only one handavailable for handling the fruit, for three of her limbs
were occupied: legs with her sleeping infant, arm forholding herself up. It seems plausible that XP may haveused CT’s foot so as not to get dirt on the surface by placing it on the ground. She would have used her own foot tohold a peeled fruit if her feet had not been occupied. This
rare behavior of XP may lead to a better understandingof plant food sharing in terms of social significance asfollows.
If CT was motivated simply to feed on lemon, hecould have easily done so on his own in the same area.
However, he chose to stay beside XP and continued topeer at her mouth. Interestingly, he did not recognize
the piece of fruit that XP put in his foot as having beenshared, or given, by her. Within 1 h before this event, CT
had groomed XP for approximately 10 min unilaterally
and followed XP intermittently, showing his strong motivation to interact with XP. These observations suggestthat it was important for CT to receive from XP what she
was eating, not what she put aside when eating. Case 1
supports the suggestion by Slocombe & Newton-Fisher(2005) that plant food sharing between adults may notalways be explained by nutritional benefits, but by social
significance.
Food sharing in Case 2 can be interpreted as a forceful event because (1) BD resisted by screaming and attempted to reclaim the food and (2) RJ showed a threatening attitude toward BD. This can be assumed as theft,
which is one of the 6 types of food transfer interactions
defined by Boesch & Boesch (1989). The availability ofT. pachysiphon fruits is not so high because chimpanzees
check and try to select ripe fruits. Thus, these fruits may
have been so attractive that RJ took them from BD. Theft

ACKNOWLEDGMENTS

Permission to conduct this research was provided by theTanzania Wildlife Research Institute (TAWIRI), Tanzania
Commission for Science and Technology (COSTECH), andTanzania National Parks (TANAPA). We are grateful to theMahale Mountains National Park (MMCRP) and MahaleGombe Wildlife Research Centre (MGWRC) for logistic
support. We thank all our research colleagues and local assistants of the Mahale Mountains Chimpanzee Research Project(MMCRP) for their continuous help and support. The present study was financially supported by MEXT KAKENHI(#24255010); JSPS KAKENHI (#14J00562 & #16J03218); andthe Leading Graduate Program in Primatology and Wildlife
Science, Kyoto University.

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Received: 8 February 2018
Accepted: 15 April 201810