increasing their access to key resources, such as food or mates.1-5 Alternatively, it has 5 been argued to be a non-adaptive result of human impacts, such as habitat destruction 6 or provisioning of food. [6][7][8][9] To discriminate between these hypotheses we compiled long-7 term information from 18 chimpanzee communities and 4 bonobo communities. Our 8 data include 152 killings (N=58 observed, 41 inferred, and 53 suspected killings) by 9 chimpanzees in 15 communities and one suspected killing by bonobos. We found that 10 males had the greatest involvement as attackers (92% of participants) and victims 11 (73%); most killings (66%) involved intercommunity attacks; and attackers greatly 12 outnumbered their victims (median 8:1 ratio). Variation in rates of killing among 13communities depended on demographic variables but was unrelated to measures of 14 human impacts. These results from all major study populations over the last five 15 decades are consistent with previously proposed adaptive explanations for killing by 16 chimpanzees but not with the human impact hypothesis. 17 18Conspecific killing has been documented at multiple chimpanzee study sites, 2-5,10-12 but rates 19 vary greatly among sites. The human impact hypothesis and the adaptive strategies 20 hypothesis yield contrasting predictions, which we test here (Tables 1, 2). The human impact 21 hypothesis states that killing occurs mainly as an incidental outcome of aggression, 22 exacerbated by human activities such as providing a concentrated food resource, 23 deforestation-induced crowding, anthropogenic diseases or hunting. Accordingly, lethal 24 aggression should be high where human disturbance is high. In contrast, the adaptive strategies hypothesis views aggression as an evolved strategic 27 response by which aggressors tend to increase their fitness through increased access to 28 territory, food, mates or other benefits. [1][2][3][4][5][10][11][12][13][14][15][16][17] 45Intracommunity infanticide by females may result from intense competition among females 46 for the best feeding areas.17 Population differences in rates of killing are accordingly 47 expected to result from socioecological factors such as differences in grouping patterns 2,11 48 and/or demography.14 Lethal aggression thus occurs within a diverse set of circumstances, 49 but is expected to be most commonly committed by males; directed towards males; directed 50 6 towards non-kin, particularly members of other groups; and committed when overwhelming 51 numerical superiority reduces the costs of killing. 52 53Previous studies have developed and tested these specific hypotheses 2,5,[11][12][13][14][15][16][17] ; the present study 54 represents the first effort to test multiple hypotheses simultaneously with a comprehensive 55 dataset. To do so, we assembled data from 18 chimpanzee communities from both eastern 56 (N=12) and western (N=6) clades 24 of chimpanzees studied over 426 years (median = 21 57 years; range: 4-53) and from 4 bonobo communities studied for 92 years (media...

Although tool use is known to occur in species ranging from naked mole rats [1] to owls [2], chimpanzees are the most accomplished tool users [3-5]. The modification and use of tools during hunting, however, is still considered to be a uniquely human trait among primates. Here, we report the first account of habitual tool use during vertebrate hunting by nonhumans. At the Fongoli site in Senegal, we observed ten different chimpanzees use tools to hunt prosimian prey in 22 bouts. This includes immature chimpanzees and females, members of age-sex classes not normally characterized by extensive hunting behavior. Chimpanzees made 26 different tools, and we were able to recover and analyze 12 of these. Tool construction entailed up to five steps, including trimming the tool tip to a point. Tools were used in the manner of a spear, rather than a probe or rousing tool. This new information on chimpanzee tool use has important implications for the evolution of tool use and construction for hunting in the earliest hominids, especially given our observations that females and immature chimpanzees exhibited this behavior more frequently than adult males.

Anthropologists have long been interested in the behavioral ecology of nonhuman primates living in savannas given what we know of early hominin environments. As expected, chimpanzees in the Fongoli community in southeastern Sénégal show a unique suite of behavioral adaptations to stresses associated with their savanna habitat. While Fongoli chimpanzees are species-typical in certain regards, such as including ripe fruit in the diet during all months of the year, they also adjust their behavior to the particular stresses of this dry, hot and open environment. These behaviors include using caves as shelters during the dry season, soaking in pools of water during the hot, early rainy season, and traveling and foraging at night during maximum phases of the moon. Adult males of this 35-member community serve as focal subjects in a long-term study of the ecology and behavior of chimpanzees in a savanna-mosaic environment. Here, we report on Fongoli chimpanzee activity budgets, grouping behavior, and habitat use during the dry versus wet season based on over 2500 hours of observation from March 2005-July 2006. Findings support the hypothesis that ecological pressures associated with a savanna environment significantly affect great ape behavior. The Fongoli chimpanzees' large home range (>65km²) is sometimes used cyclically, with the community traveling as one large party, in contrast to the typical chimpanzee fission-fusion pattern. Combined with data on temperature in the various habitats within the savanna mosaic, results show that Fongoli chimpanzees minimize energy expenditure during the hottest months and at the hottest time of day by resting more and traveling less, in addition to selectively using small patches of closed-canopy habitats, such as gallery forest. They move significantly more during early hours of the hot, dry season specifically and range in smaller parties at this time compared to during the wet season. The stresses associated with a savanna-mosaic environment and chimpanzees' behavioral adjustments to them have important implications for understanding early hominin behavior in similar environments.

Chimpanzees (Pan troglodytes) make nests for resting and sleeping, which is unusual for anthropoid primates but common to all great apes. Arboreal nesting has been linked to predation pressure, but few studies have tested the adaptive nature of this behavior. We collected data at two chimpanzee study sites in southeastern Senegal that differed in predator presence to test the hypothesis that elevated sleeping platforms are adaptations for predator defense. At Assirik in the Parc National du Niokolo-Koba, chimpanzees face four species of large carnivore, whereas at Fongoli, outside national park boundaries, humans have exterminated almost all natural predators. We quantified the availability of vegetation at the two sites to test the alternative hypothesis that differences in nesting reflect differences in habitat structure. We also examined possible sex differences in nesting behavior, community demographic differences, seasonality and nest age differences as variables also potentially affecting nest characteristics and nesting behavior between the two sites. Chimpanzees at Fongoli nested at lower heights and farther apart than did chimpanzees at Assirik and sometimes made nests on the ground. The absence of predators outside of the national park may account for the differences in nest characteristics at the two sites, given the similarities in habitat structure between Fongoli and Assirik. However, Fongoli chimpanzees regularly build arboreal nests for sleeping, even under minimal predation pressure, and this requires explanation.

The eect of food resources on behavior has been dicult to measure. Here we use animals themselves to describe``eective'' food abundance and distribution by comparing, relative to where individuals stopped to eat, movements of (1) adult females living in a small group of vervet monkeys (Cercopithecus aethiops) with those living in a large group and (2) vervets and patas monkeys (Erythrocebus patas). Although females in the large vervet group travelled farther and stopped to eat more often than females in the small vervet group, these dierences resulted from foraging in Acacia drepanolobium habitat. In A. xanthophloea habitat, females in the large group travelled less far, travelled shorter distances between foods, and stopped as often as females in the small group. Greater foraging costs of females in larger vervet groups may be oset by access to home ranges of better quality. Compared to patas, vervets travelled shorter distances, moved shorter distances between food sites, stopped less often, and had longer feeding bouts, suggesting that foods of vervets are denser and larger, overall, than foods of patas. When vervets foraged in A. drepanolobium habitat, also the habitat of patas, their foraging behavior became more like that of patas. Vervets travelled farther, stopped more often, and spent less time at food sites in A. drepanolobium habitat than in A. xanthophloea habitat, suggesting that foods are smaller and less usurpable in A. drepanolobium habitat. Distance between foods, a component of food distribution, did not increase, however. The critical variable underlying usurpability of foods may be food site depletion time, a temporal measure.

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For anthropologists, meat eating by primates like chimpanzees (Pan troglodytes) warrants examination given the emphasis on hunting in human evolutionary history. As referential models, apes provide insight into the evolution of hominin hunting, given their phylogenetic relatedness and challenges reconstructing extinct hominin behaviour from palaeoanthropological evidence. Among chimpanzees, adult males are usually the main hunters, capturing vertebrate prey by hand. Savannah chimpanzees (P. t. verus) at Fongoli, Sénégal are the only known non-human population that systematically hunts vertebrate prey with tools, making them an important source for hypotheses of early hominin behaviour based on analogy. Here, we test the hypothesis that sex and age patterns in tool-assisted hunting (n=308 cases) at Fongoli occur and differ from chimpanzees elsewhere, and we compare tool-assisted hunting to the overall hunting pattern. Males accounted for 70% of all captures but hunted with tools less than expected based on their representation on hunting days. Females accounted for most tool-assisted hunting. We propose that social tolerance at Fongoli, along with the tool-assisted hunting method, permits individuals other than adult males to capture and retain control of prey, which is uncommon for chimpanzees. We assert that tool-assisted hunting could have similarly been important for early hominins.