Dora Biro, Tatyana Humle, Kathelijne Koops, Claudia Sousa, Misato Hayashi, Tetsuro Matsuzawa
Chimpanzee mothers at Bossou, Guinea carry the mummified remains of their dead infants.
Current Biology, Volume 20, Issue 8, R351-R352, doi: 10.1016/j.cub.2010.02.031
The forests surrounding Bossou, Guinea, are home to a small, semi-isolated chimpanzee community studied for over three decades . In 1992, Matsuzawa  reported the death of a 2.5-year-old chimpanzee (Jokro) at Bossou from a respiratory illness. The infant's mother (Jire) carried the corpse, mummified in the weeks following death, for at least 27 days. She exhibited extensive care of the body, grooming it regularly, sharing her day- and night-nests with it, and showing distress whenever they became separated. The carrying of infants' corpses has been reported from a number of primate species, both in captivity and the wild , , ,  and  — albeit usually lasting a few days only — suggesting a phylogenetic continuity for a behavior that is poignant testament to the close mother-infant bond which extends across different primate taxa. In this report we recount two further infant deaths at Bossou, observed over a decade after the original episode but with striking similarities.
During the 2003 dry season, a respiratory epidemic broke out at Bossou, claiming the lives of five chimpanzees (reducing their number from 19 to 14) . Among the dead were two infants: 1.2-year-old Jimato and 2.6-year-old Veve (see Supplemental Information available on-line with this issue). The mothers of both infants (Jire and Vuavua) continued to carry their offspring's lifeless bodies for 68 and 19 days after death, respectively (Figure 1A; Table S1). Thus, for the first three weeks of January 2004, Bossou was home to two mothers carrying dead infants.
As in Jokro's case, the bodies of Jimato and Veve underwent complete mummification. Over the days following death, the bodies swelled, then gradually dried out. All hair was lost, but body parts remained largely intact, encased in dry leathery skin. When it was finally abandoned, Veve's skeleton was still remarkably intact, missing only some teeth in the upper jaw (Figure 1B). Because of the wearing effects of prolonged carrying, by the time Jire abandoned Jimato's body, much of the bony cranial structure had been destroyed, making most facial features unrecognizable. Nevertheless, fingers, toes, and even genitals were preserved within the layer of tough dry skin.
In all three cases, group members' responses to the corpses were highly similar. Mothers carried the bodies during all travel (typically by gripping a limb in hand, foot, or between shoulder and neck), groomed them regularly, and chased away flies that circled the corpses (twice with the aid of a tool; Supplemental Movie S1). These are all behaviours that may have facilitated mummification. Related and unrelated individuals from all age groups and both sexes attempted to touch, poke or handle the bodies, lifted and dropped their limbs, and sniffed them. In later stages, juveniles and infants were occasionally allowed to carry the bodies some distance from the mother in bouts of play (Supplemental Movie S2). With only one exception (Movie S2), we never observed a response that could be interpreted as aversion, despite the bodies' intense smell of decay and highly unusual appearance. Similarly, we observed no aggressive acts towards the infants' corpses during the entire period of carrying. Elsewhere, chimpanzees have been reported to treat violently and even cannibalise the corpses of dead infants after snatching them away from the mother shortly after death (for example  and ). No such incidents were recorded in the cases of Veve and Jimato. In general, therefore, all members of the community demonstrated high levels of tolerance towards the corpses.
What factors were responsible for the mothers finally abandoning the corpses? Besides accidental loss of the bodies and subsequent failure to recover, physiological changes in the mothers associated with infant-death may also have played a role. Postpartum amenorrhoea in chimpanzees lasts around four years, but is much shortened after an infant's death . Because lactation ceased once the infants died, the mothers' reproductive cycle returned; such hormonal changes, which prepare the mother for the arrival of a new infant (normally around weaning), may have contributed to a gradual ‘letting go’ of the previous infant's remains. Intriguing parallels may exist with physiological and psychological changes experienced by human mothers, in whom the absence or cessation of breastfeeding may cause exaggerated desires to hold their infant . The fact that Jire nonetheless carried her infant for considerably longer than Vuavua may have been rooted in several factors, including Jire's extensive experience as a mother (Jimato was her eighth infant; Veve was Vuavua's first) and Jimato's younger age at death.
An obvious and fascinating question concerns the extent to which Jire and Vuavua “understood” that their offspring were dead. In many ways they treated the corpses as live infants, particularly in the initial phase following death. Nevertheless they may well have been aware that the bodies were inanimate, consequently adopting carrying techniques never normally employed with healthy young (although mothers of handicapped young have also been known to respond appropriately). The fact that all three documented cases of infant deaths at Bossou were followed by extended carrying of the infants' remains suggests that this behaviour may not be a rare occurrence in this small community, and raises questions about the potential role of observational learning in promoting chimpanzee mothers' prolonged transport of deceased young. Nonetheless we hope that further data from this already threatened community will not be quick in coming.
We are grateful to the Direction National de la Recherche Scientifique et Technique, République de Guinée, for permission to conduct field work at Bossou, to Akino Kato-Watanabe and to local guides Guanou Goumy, Tino Zogbila, Paquilé Cherif, Pascal Goumy, Marcel Doré, Boniface Zogbila, Jules Doré, and Henry Camara for assistance in the field. The research was supported by Grants-in-Aid for scientific research from the Ministry of Education, Science, Sports, and Culture of Japan (grants 07102010, 12002009, 10CE2005, and the 21COE program). D.B. was supported by a Royal Society University Research Fellowship and by Somerville College, Oxford. K.K. was supported by a grant from the Lucie Burgers Foundation for Comparative Behavioural Research (Netherlands) and T.H. by an NIH Kirschstein-NRSA Postdoctoral Fellowship (MH068906-01).
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