Responses of chimpanzees to a recently dead community member at Gombe National Park Tanzania.код для вставкиСкачать
American Journal of Primatology 74:1–7 (2012) COMMENTARY Responses of Chimpanzees to a Recently Dead Community Member at Gombe National Park, Tanzania FIONA ANNE STEWART1, ALEXANDER KENNETH PIEL2, AND ROBERT C. O’MALLEY3 1 Department of Biological Anthropology, Leverhulme Centre for Human Evolutionary Studies, University of Cambridge, Cambridge, United Kingdom 2 Department of Anthropology, University of California-San Diego, La Jolla, California 3 Department of Biological Sciences, University of Southern California, Los Angeles, California Chimpanzee responses to the death of a group member have rarely been observed in the wild and most instances involve infant deaths. One of the very few detailed accounts of a group’s response to the death of an adult community member is from Gombe National Park, Tanzania, where Teleki [Folia Primatologica 20:81–94, 1973] observed the responses of 16 chimpanzees to an accidental death, none of whom touched the body. Now, almost 40 years later, we report on the behaviors of 16 (different) Gombe individuals to the recently dead body of an adult female community member. In stark contrast to Teleki’s account, we observed individual chimpanzees’ responses to range from curious observation and passive investigation (e.g. smelling and grooming) to the shaking, dragging, and frustrated beating of the body. Variation across demographic groups is described and may reflect individuals’ past experience with death. The implications of our observations are discussed in the context of core morbidity traits shared between humans and chimpanzees. Am. J. Primatol. 74:1–7, 2012. r 2011 Wiley Periodicals, Inc. Key words: chimpanzees; death; gombe; morbidity INTRODUCTION Humans exhibit diverse cultural variation in mortuary practices [Huntington & Metcalf, 1979], where treatment of dead bodies ranges from their consumption, to the placing of them as far above or below ground as possible [Martin, 1996]. Some treatment patterns, however, are more universal and consistent with sociobiological explanations. For example, Littlefield and Rushton  showed that (across Canada) mothers grieve more intensely than fathers, and both grieve more intensely for men than women. Healthy children will be grieved over more intensely than unhealthy children, and parents with fewer children will grieve more intensely than those with many children. Additionally, the type of death, relationship characteristics between the dead and the survivor, and the social circumstances surrounding the death also influence human responses [Parkes, 1985]. This variation can be observed in response intensity, duration, or whether the entire process is immediate or delayed after the death. Other animals exhibit diverse responses to the death of conspecifics. Responding to the same polyamines [Pinel et al., 1981], ants and rats both remove the dead from their burrows, carrying them out or burying them, respectively. Dolphins show both sociosexual behavior and aggression to carcasses [Dudskinski et al., 2003], whereas elephants consistently express behaviors of ‘‘concern’’ (e.g. r 2011 Wiley Periodicals, Inc. monitoring and sniffing the carcass [Douglas-Hamilton et al., 2006]. Across the primate order, most examples describe responses to dead infants, although not all. Over 40 years ago, Cowgill  described how a pair (alpha male and female) of captive pottos (Perodicticus potto) began to ration food for a recently dead (and subsequently removed) b male cage-mate, seemingly searching the enclosure regularly for months after the death. Perhaps no species has seen the history, and more recent explosion, of reports on behavioral responses to death as has chimpanzees (Pan troglodytes). Recent descriptions include accounts on observations from three research settings: captive [Anderson et al., 2010], sanctuary [Cronin et al., 2011], and wild [Biro et al., 2010] populations. These reports build on previous accounts [Boesch & Boesch-Achermann, Contract grant sponsor: Jane Goodall Institute. Additional Supporting Information may be found in the online version of this article. Correspondence to: Alexander Kenneth Piel, Department of Anthropology, University of California-San Diego, La Jolla, CA 92093-0532. E-mail: email@example.com Received 8 June 2011; revised 20 July 2011; revision accepted 21 July 2011 DOI 10.1002/ajp.20994 Published online 28 October 2011 in Wiley Online Library (wiley onlinelibrary.com). 2 / Stewart et al. 2000; Goodall, 1968; Kooriyama, 2009; Matsuzawa, 1997; reviewed in Pettitt, 2011] of chimpanzee responses to death, almost exclusively to infants and juveniles. Matsuzawa et al.  describe coming across the carcass of a 6.5-year-old male with 20 individuals sitting around it in Bossou, Guinea, although few other data are provided. In the same community, Biro et al. [2010, p R351] describe the extended carrying of dead infants by their mothers at the same site, where individuals of all age-sex classes ‘‘attempted to touch, poke, or handle the bodies,’’ but not to carry them. Infants were carried for up to 68 days after the infant’s death. In contrast to other observations from the wild (see below), no aggression was ever observed toward the carcasses at Bossou. In one of the rare observations of chimpanzee responses to the death of an adult, Anderson et al.  described captive chimpanzee behavior at Blair Drummond Safari Park, Scotland. Unique to this report were the detailed observations made from video before, during, and after the death. The authors describe behaviors that are analogous to those that humans exhibit: chimpanzees appeared to care for the individual before death, test for signs of life at the point of death, and post-death showed signs of frustration, and subsequent avoidance of the location where the death occurred. They proposed that their observations differed in several ways from previous accounts. First, while reports from Gombe [Teleki, 1973] and Tai [Boesch & Boesch-Achermann, 2000] describe excited and aggressive behaviors by conspecifics around (or in Tai toward) the corpses in response to death, Anderson et al. [2010, p R350] observed subdued, calm behaviors, ‘‘strikingly reminiscent of human responses to peaceful death.’’ Additionally, at both Tai and Gombe, chimpanzees exhibited noticeable interest in the carcass and the place of death, even dragging the body over short distances at Tai. The opposite response was seen in captivity in Scotland, where individuals avoided the place of death for five consecutive days despite having slept there the 29 previous nights. The observations from this small group in captivity prompted Anderson et al.  to question whether empathy, self-awareness, and cultural variation— traits shared by humans and chimpanzees—allow us also allow a shared awareness of death [see also Boesch & Boesch-Achermann, 2001]. Finally, a recent report from Chimfunshi Wildlife Orphanage Trust, Zambia represents one of the first descriptions that quantifies mother responses to their dead infants. Although infant carrying is a ubiquitous behavior across chimpanzee communities, Cronin et al. [2011, p 420] recognized there is a paucity of evidence that examines how, in this transitional process, a mother distances herself from the infant carcass. Measuring the proximity and interaction between mother and dead infant across time, the authors suggest that these types of observed behaviors may Am. J. Primatol. specifically inform on ‘‘how chimpanzees respond to the premature severing of the mother–infant bond.’’ Fashing et al.  detailed the responses of wild gelada monkeys (Theropithecus gelada) to dead infants. Females carried dead infants for 1–4 days before abandoning the body, but geladas in general exhibited limited or no interest in the death of adult or juvenile conspecifics. The authors also describe the death of a mother–infant pair whose physical weakness eventually prevented them from keeping up with troop movements. On the first day the pair failed to follow the troop, group members looked back often in the direction of the pair, but eventually moved on to forage. Even upon return to the sleeping site where the geladas had all slept the night before, the authors observed no evidence of any attempt to locate the weakened individuals. The mother died first, infant at her side. Researchers found the dead infant alone the following morning [Fashing et al., 2011]. The authors proposed two explanations for different responses to death across primates. The first is ecological, that perhaps extreme (cold or dry) climates contribute to delayed decomposition of carcasses, and thus prolonged interest from group members [Fashing et al., 2011; Matsuzawa, 1997]. The second is phylogenetic, that these more complex responses to death (see below) may reflect an ancestral trait of hominoids only [Warren & Williamson, 2004; Whilde & Marples, 2011; reviewed in Pettitt, 2011]. Besides that of Anderson et al. , the only other documented report of chimpanzee responses to adult deaths comes from Teleki’s  observations from Gombe. He described in detail the responses of chimpanzees to the sudden and dramatic death of a community member, Rix, who fell from a tree and broke his neck. Behavioral responses varied between individuals, and were hypothesized to vary with age or social relationship. Some individuals stayed with the corpse for many hours, but avoided touching it, and almost all made ‘‘wrah’’ calls, prompting Teleki to conclude that such vocalizations may have a special significance in the context of a dead community member. Here we contribute another case study to this growing list of observations, describing and quantifying the responses of chimpanzees to a dead adult female conspecific in natural conditions in Gombe. Given most sick or wounded animals retreat from their social group shortly before death [Hart, 1988], detailed observations from the wild are rare and difficult to record. We describe here the responses of 18 individuals to a recently deceased adult female, Malaika, of the Kasekela community. The presence of many community members allowed our detailed recording of individual responses and sequential quantitative analysis of how individuals of different age and sex classes varied in interest and arousal around the corpse. Additionally, we explore Pettitt’s  developmental periods of mortuary phases (Core; Archaic: Modernizing; Modern; Advanced) in Responses to a Dead Community Member in Chimpanzees / 3 wild chimpanzee responses to an adult community member. METHODS Study Site and Data Collection Gombe National Park —35 km2 and the site of one of the longest continuous field studies of wild chimpanzees—is situated along the eastern shore of Lake Tanganyika [Goodall, 1986]. At the time of data collection, there were three communities in the park: Mitumba in the north, Kasekela in the center, and Kalande in the south [Pusey et al., 2007]. All observations come from the Kasekela community, which numbered 60 individuals (12 adult, 6 adolescent, 2 juvenile and 6 infant males, and 20 adult, 8 adolescent, 1 juvenile and 5 infant females) at the time of the observation. Data were collected on a party of 18 individuals (Fig. 2; 7 females, 10 males, and 1 infant). The dead individual, Malaika, was approximately 20 years old and had one known living offspring, a daughter, Mambo, born into the Kasekela community in 2004 [Wilson et al., 2005]. Malaika immigrated into the community in 2002, but remained low ranking and appeared to be socially peripheral [Murray et al., 2007; O’Malley, pers. obs.]. The research complied with protocols approved by the Tanzanian National Parks) authority, the Commission on Science and Technology, and Tanzania Wildlife Research Institute as well as adhered to the American Society of Primatologists Principles for the Ethical Treatment of Non Human Primates. Malaika’s body was discovered on January 5, 2010 in Mkenke Valley by Tanzania National Parks Chimpanzee Trackers. She had been visibly weak, ill, and was mostly solitary for several days leading up to her death (Emma Lantz, pers. comm.), and she was estimated to have died the previous night or early that morning based on the absence of flies or signs of decomposition known to occur rapidly in forest environments [Boesch & Boesch-Achermann, 2000]. F. A. S. and A. K. P. arrived at 0915 hr to find Malaika’s corpse and a party of chimpanzees already present. All behavior near the corpse was documented ad libitum with videography and written notes. The video camera (Sony Handycam DCR-SR82) was handheld and remained trained on the body to capture all interactions and activities in close proximity to it. Videography was interrupted between 1116 hr and 1230 hr due to low battery warnings and resumed until 1300 hr. For the entire observation period, all individuals present, their behavior, and in particular any interest and each physical contact with the body were recorded ad libitumusing written notes and later verified against the video footage. Individuals were identified on sight by National Parks Chimpanzee Trackers and Gombe Research Assistants and on video later confirmed by RCO. Owing to the difficulty of simultaneously recording behaviors of all the individuals present, observations focused on individuals interacting with the body directly or who were within approximately 20 m of it. Following Teleki , and in order to directly compare frequency of behaviors, total time was segmented into 15-min intervals to assess the presence and frequency of behaviors. The number and identity of individuals observed to perform any of six categories of behavior during each 15-min interval were used for analyses. Categories of behavior included investigate, play, vocalize, rest, feed, and display. ‘‘Investigate’’ refers to behaviors directed toward the corpse, and as defined by Teleki included the behaviors ‘‘watch’’ and ‘‘sniff’’ only. We have included a wide range of behaviors, which were grouped into five sub-categories describing magnitude of investigation, ranging from passive to intensive: watch, sniff, poke genitals and sniff fingers, groom, gentle-handle, rough-handle. Gentlehandle included touch, stroke, hold hand, or embrace body. Rough-handle included shake, hit, slap, stamp on, and drag body. Following the removal of the body, ‘‘investigate’’ refers to behaviors directed toward the last spot where the body had lain. The number of 15-min intervals within which an individual was observed to perform each of these behaviors was used for analyses of variation with individual age. In order to control for an individual presence, the number of 15-min intervals in which an individual was present within observation range was also recorded, and the proportion of 15-min intervals in which investigative behaviors occurred was calculated for each individual. RESULTS From 0915 until 1227 hr, 18 individuals interacted to varying degrees with Malaika’s body (Figs. 1 and 2). At 0915 hr, her body lay prone on the ground near a dry streambed while a juvenile slapped her body on the ground (Movie ESM1) and five individuals watched silently from arboreal locations. One night nest was nearby, and although unknown if this was Malaika’s from the previous night, the absence of other nests in the vicinity suggests that most of the chimpanzees arrived at the site that morning. The alpha male, Ferdinand, displayed with the body at 0928 hr, throwing her down into the streambed. This display was one of several by different males. Malaika was visited by a succession of individuals who one by one, briefly investigated the body, while other individuals continued to watch from above. Periodically young males dragged her body. Soon thereafter, eight individuals formed a tight circle around the body beneath a thicket in silence. Most were only looking, but a few sniffed or groomed the body. During the observation period, her body was also Am. J. Primatol. 4 / Stewart et al. Fig. 1. Number of individuals who performed behaviors during 15-min intervals. The black line indicates the time of removal of Malaika’s body, after which "Investigate" occurs toward the body’s last location. (Individual ages are from Wilson et al. ). Fig. 2. Number of 15-min intervals individuals, grouped by sex and age [Teleki, 1973], were present (black line) and were observed to watch, sniff, groom, poke genitals, and sniff fingers, gentle-handle, or rough-handle Malaika’s body (stacked bars). sequentially monopolized by individual young males, which displaced younger chimpanzees. Persistent rough-handling of Malaika’s body by these young males suggests that they may have been frustrated with her lack of response, or else were using her body as a tool in displaying to community members [Teleki, 1973]. Malaika’s body was never left alone, and was eventually dragged over 60 m by at least four individuals. This dragging (Movie ESM 2) sometimes appeared as attempts to monopolize access, as individuals dragged the body away from others, while at other times, as attempts to haul the corpse with the party after other individuals had begun to travel. The number and identity of individuals who performed any of six categories of behavior during 15-min intervals are shown in Figure 1. Feed, rest, and play were infrequent, although the slight increase in rest over time may indicate a gradual loss of interest in the carcass. Displays toward and around the corpse were also infrequent in contrast to previous accounts [Teleki, 1973]. ‘‘Waa’’ and ‘‘wraa’’ Am. J. Primatol. calls were the most distinctive of frequent vocalizations, suggesting high levels of arousal and distress. The most notable difference between previous accounts and ours concerns levels and type of interaction with the corpse. Teleki  reported low levels of investigation (never more than two individuals in any 15-min period), whereas up to eight individuals inspected or manipulated the body in any 15-minute period during our observations. Teleki also observed no tactile inspection, whereas we saw a wide range of exploratory acts, ranging from passive (watch) to intensive (roughhandle—Fig. 2), more similar to observations made by Boesch and Boesch-Achermann . These ‘‘passive’’ forms are part of the natural chimpanzee behavioral repertoire, while the ‘‘intensive’’ are unusual for any within-group context, wild or captive. Individuals of all ages and both sexes intently watched the body, and except for three females and two males, all sniffed it. No females except Malaika’s daughter, Mambo, handled the body. Males rough-handled the body significantly Responses to a Dead Community Member in Chimpanzees / 5 more frequently than females (Mann–Whitney U test, U 5 14, n1 5 7, n2 5 10, P 5 0.016, two-tailed), and younger males more than older males (Spearmans, r 5 0.731, n 5 10, P 5 0.016, two-tailed). Younger males also groomed the body and tended to gentlehandle her more than older males (r 5 0.787, n 5 10, P 5 0.007, and r 5 0.57, n 5 10, P 5 0.085, two-tailed). These sex-differences and correlations with male age remain significant if controlled for the amount of time spent within the vicinity (roughhandle sex difference: U 5 14, P 5 0.016; roughhandle vs. male age: r 5 0.71, P 5 0.022; groom vs. male age, r 5 0.77, P 5 0.009), with the exception of rough-handle which then does not correlate with male age (r 5 0.53, P 5 0.12). Malaika’s body was removed by Gombe researchers at 12:38 hr, after all chimpanzees had moved away from the body. However, some individuals probably remained 40 m away and watched the body being packaged and removed. After it was removed, eight individuals immediately returned to the last location of the corpse. Five individuals inspected where the corpse had lain by touching and sniffing the ground. Fudge was the first to approach, arboreally, and looked down to where the body had lain. He began a pant hoot that was joined in chorus by the individuals present. This is reflected in the peak of the number of individuals vocalizing during these two 15-min intervals (Fig. 1), of which vocalizations included pant hoot chorus, wraa call, and whimper (wraa and whimper indicating distress). Mambo was the last to inspect the site, while Sparrow and Ferdinand waited a few meters away before the party finally departed at 1300 hr. DISCUSSION Attitudes Toward Death These observations lend themselves to comparisons from previous accounts. Hosaka et al.  discuss the diversity of ways chimpanzees respond to the death of community members at Mahale. They suggested that the level of decomposition and cause of death influence emotional state, ranging from fear to curiosity, with females and juveniles tending toward the former and males the latter. Those emotions are then expressed through vocalizations, most notably in ‘‘wraa’’ or ‘‘huu’’ calls. Mahale males were often aggressive with carcasses, using them in display behaviors. It is noteworthy that chimpanzees exhibit similar behaviors also to the carcasses of other animals, while other primates seem to pay little attention to such carcasses [e.g. vervet monkeys, Struhsaker, 1967]. This suggests a ‘‘broad curiosity’’ by chimpanzees whereby they are constantly learning about their surroundings [Cronin et al., 2011; Hosaka et al., 2000]. Cronin et al.  described chimpanzees’ investigation of a dead infant’s hands and face as providing tactile, olfactory and potentially gustatory signs, possibly to assess the current state of the body. At Tai, Boesch and Boesch-Achermann  describe how chimpanzees often lick the blood of chimpanzees that have been injured, but not from those recently dead, thus differentiating between the two states. Teleki  suggested that ‘‘the behavior of certain individuals [y] seemed to indicate awareness of a change from activity to inactivity of a group member, but it remained uncertain whether any participant grasped the conceptual difference between life and death’’ and Pettitt’s  interpretation of Tai chimpanzees’ responses to the death of a 10-year-old juvenile (Tina)—which included unusual vocalizations, sitting silently, grooming, displaying, and dragging her body–is that ‘‘something very different is occurring at the death site.’’ That is, individuals exhibit a range of behaviors, otherwise not seen in a single context. He concluded ‘‘chimpanzees appear to be aware that death has occurred.’’ The passivity of adult chimpanzees to Malaika’s body could also suggest an understanding of Malaika’s change of state, but quantitative comparison of changes in behavior toward an individual pre- and post-death are necessary to test these hypotheses. The younger individuals’ persistent and aggressive physical manipulation of the body suggested frustration and possible exaggerated attempts to arouse Malaika. Anderson et al.  also suggested this type of inspection and male aggression toward the corpse may reflect attempts to resuscitate the body. Alternatively, these behaviors could be interpreted as curiosity at a nonresponsive conspecific. What can we learn from this diverse behavioral repertoire in chimpanzees to the death of community members? Littlefield and Rushton  showed that variation in type and intensity of response to death in humans is influenced by the sex of the dead and griever, as well as the type of death, circumstances surrounding the event, and the nature of the relationship between griever and the deceased. As Malaika was an immigrant and relatively lowranking [Murray et al., 2007], she may not have had strong relationships to any nonkin in Kasekela. As might be predicted, then, Mambo’s behavior differed from all others. She watched more continuously, from closer distance, and was the only female to handle Malaika. She visited the carcass frequently, but briefly as she was often displaced or distracted by play. Mambo also participated in nine of ten observed play bouts. To Littlefield and Rushton’s list, we propose that we should add the age of the griever, at least for chimpanzees. Our observations showed that females and older males interacted less with the corpse. Sparrow’s high level of interest may result from her Am. J. Primatol. 6 / Stewart et al. son’s (Sinbad) persistent handling of Malaika. Eowyn, a juvenile female, that watched only, is known to have experienced her mother’s death (M. Wilson, pers. comm.). One possibility is that older individuals have previously experienced death, thus exhibiting less interest. Alternatively, younger individuals may exhibit also more exploratory behaviors across a range of contexts if they have generally higher levels of curiosity and lower levels of neophobia. That there is variation in responses to death across age and sex classes provides a possible avenue for testing these hypotheses using pre- and post-death comparisons of individual behavior in the wild (if the opportunity unfortunately arises). Implications for Early Hominid Morbidity The behavior of chimpanzees should not be misinterpreted as that of the last common ancestor of great apes and humans. Nonetheless, in a similar way that contemporary human behavior at funerals includes ritual practices that are context-specific (regardless of variation across cultures), so might a context-specific behavioral repertoire accompany chimpanzees in response to the death of a community member. Similarities across these two closely related species may reveal shared ancestral tendencies. Specifically, Pettitt  has argued that observations of other primates can help us to identify core behaviors toward the dead that may reflect our evolutionary history. These include, but are not restricted to 1. Cronus compulsions—the urge to dismember, injure, or consume parts of bodies of conspecifics; 2. Manifestations of morbidity (As defined by Pettitt [2011, p 8] as ‘‘an enquiring concern with the injured, diseased, or dead body, whether or not this derives from a desire to understand the nature or cause of death of an individual.’’)— especially by those with a close relationship to the corpse, in the form of grooming usually; 3. Manifestations of mourning—here possibly expressed in distress vocalizations (e.g. ‘‘wraa’’ barks), carrying the corpse as a sign of detachment; 4. Social theater around the corpse, including controlled access to the body. Our observations, like some previous [e.g. Anderson et al., 2010], of the responses to Malaika’s death include examples of all of these. (This includes, according to Pettitt , controlled access of the corpse, sometimes using it in displays. Behaviors here are not observed in other contexts and can also be termed ‘‘funerary gatherings.’’) Although historically there have been few reports of primates responding to the death of group members, this trend is changing, and the last 2 years Am. J. Primatol. especially have seen a wave of descriptions, both from captive and wild settings, and to infants and adults alike. Combined, these observations not only shape what Anderson  proposes to be a ‘‘primatological perspective’’ on death, but also reveal intra- and interspecific similarities in the treatment of conspecific dead bodies. These patterns, in turn, lend themselves to reconstructing the origins of human responses to death. 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