Deceptive Tactic by an Adult Male Chimpanzee to Snatch a Dead Infant from its Mother.
Toshisada Nishida
Laboratory of Human Evolution Studies,
Kyoto University

INTRODUCTION
The ability of deception (defined here as the misleading of other individual(s) for one's own advantage by expressing postures, gestures, and facial expressions that are irrelevant to the context) has been proposed as the explanation of certain chimpanzee behavior (2,3). Under natural conditions, proving the existence of deception is extremely difficult. However, if the behavior is linked to some unusual behavior, the burden of proof will be lowered. The episode mentioned below occurred with the unusual behavior of cannibalism.

METHODS
In 1992 I studied the M group chimpanzees from Aug. 11 to Nov. 5. During this period, I selected one of the adult males as a target every morning and followed him as long as possible. The incident occurred during the beginning of my (intended) focal observation of the beta male, Nsaba. However, the description also merits from my ad-lib sampling data and the video document of the victim before the focal sampling began. The video team led by Miho Nakamura had been shooting the victim because she was dying of unusual injury inflicted upon her.

OBSERVATIONS
Garbo, 41-months-old daughter of Gwamwami, had lost her foot by 31st of July (Hayaki, unpublished). Although the cause of the loss was unknown, it was likely the result of an attack by a male chimpanzee. Garbo sometimes found it difficult to travel, but was helped by her mother whenever she did so. When I started my study on August 11, she appeared completely healthy despite her handicapped foot since virtually all of her nourishment came from her mother's milk.
On September 1, the observation of the chimpanzees began at 08:30 in the morning. Perhaps as a result of a fresh wound on the waist inflicted in a new attack on her, Garbo had been incapacitated to move on her own and instead was being carried by her mother. She whimpered in a feeble voice as Gwamwami traveled above the ground. Meanwhile, the infant closed her eyes.
At 09:05, Garbo died. Gwamwami carried the body by supporting it with her thigh, climbed down the ground, and transported it with her right arm. A juvenile male, Nick, came close to inspect the body. So many chimpanzees were interested in the dead infant and came closer to Gwamwami that she fled with the body in her right arm. A sub-adult male, Masudi, approached Gwamwami. Then, three adult males including the alpha male, Ntologi, came and began to groom her. Ntologi groomed her for more than 2 minutes, while Gwamwami put her dead infant on the ground, or groomed it. A juvenile male, Iwan, came and lied supine on the ground close to Gwamwami and glanced at the body from time to time.
There was a display by adult males, and chimpanzees were scattered. Subsequently, she moved deeper into the bush to avoid her companions. Meanwhile, a few chimpanzees, including Nsaba, Toshibo (5th ranking male) and Bembe (8th ranking male), were within 10 m of Gwamwami. Nsaba sat quietly 5 m apart from her. At 09:35 Nsaba finally came closer to Gwamwami and began to groom her on the back. At 09:42, Nsaba suddenly reached out with his hand and pushed Gwamwami on the back. When the body fell to the ground, he snatched the dead baby. Immediately, Gwamwami ran after him, screaming. Simultaneously <Wrraah> calls and barks occurred. Although Gwamwami ran after Nsaba, two adult males, Toshibo and Kalunde (3rd ranking), prevented her from following Nsaba. They made displays against Gwamwami and drove her off to above the ground. During this period, Nsaba succeeded in running away. Although we ran after him, we lost sight of him and could not find Nsaba again that day. At 09:48, when I found Gwamwami again, she limped with her left hand injured and a young adult male, Fanana, was hanging around her, to whom she pant grunted.
Our concern was, of course, the purpose of his snatching. What is the body to him? The most likely answer was that the body is meat to him, although we had never seen chimpanzees eating dead conspecifics (cannibalism after killing infants had been observed seven times(1)). The next day, I asked one of the assistants to search for Nsaba and to pick up his feces wherever they were available. Around noon of that day (namely, 26 hours after Nsaba had disappeared), the assistant obtained the feces of Nsaba. We washed the feces and found black chimpanzee hairs. Nsaba most likely snatched the body in order to eat the meat. Moreover, it appeared to me that Nsaba deliberately approached Gwamwami while concealing his intention to snatch the dead infant.

DISCUSSION
My hypothesis is that Nsaba had concealed his intention to snatch the body when he approached Gwamwami. The alternative, parsimonious hypothesis may be that as she groomed her, his desire for meat increased gradually until he at last grabbed it. This possibility is unlikely. First, Nsaba was grooming the back of Gwamwami from the onset to the end, and from that position he could not see the body that was in the lap of the mother. Second, the smell of the body was not there within 1 hr after the death. Really, my first impression of grooming by Nsaba was that he was such a tender male to groom a female who had just lost her baby. He appeared to be considerate of the mother's feelings and to be patient enough to wait for some minutes until the mother was relaxed to some extent. All I was thinking of was Nsaba's tender thoughtfulness.
My interpretation suddenly changed: Nsaba must have cherished his idea of stealing and eating the body long before his sudden assault. He was concealing his intentions not only while he was waiting before he began to groom her. He continued to conceal his intentions during his 7 minutes of grooming. He must have been waiting for the opportunity to take the body until the mother became so relaxed that her caution disappeared.
Nsaba's attitude was different from the other males such as Ntologi. When Gwamwami was being groomed by Ntologi, she occasionally put her charge just beside her on the ground. It would have been far easier to grab it rather than if it had been in the mother's lap. Therefore, it is likely that most males did not consider the body as meat.
The research was funded under the Monbusho International Scientific Research Program (#03041046 to TN).

REFERENCES
  1. Hamai, M, Nishida, T, Takasaki, H & Turner, LA 1992. New records of within-group infanticide and cannibalism in wild chimpanzees. Primates 33: 151-162.
  2. Mitchell, RW & Thmpson NS (eds.) 1985. Deception. SUNY Press, Albany.
  3. Nishida T. 1990. Deceptive behavior in young chimpanzees: An essay. In: The Chimpanzees of the Mahale Mountains. T. Nishida (ed.), The University of Tokyo Press, Tokyo, pp.285-290.

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