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Gruber, T., Clay, Z., & Zuberbühler, K. (2010). A comparison of bonobo and chimpanzee tool use: evidence for a female bias in the Pan lineage. Anim. Behav., 80(6), 1023–1033.
Abstract: Chimpanzees, Pan troglodytes, are the most sophisticated tool-users among all nonhuman primates. From an evolutionary perspective, it is therefore puzzling that the tool use behaviour of their closest living primate relative, the bonobo, Pan paniscus, has been described as particularly poor. However, only a small number of bonobo groups have been studied in the wild and only over comparably short periods. Here, we show that captive bonobos and chimpanzees are equally diverse tool-users in most contexts. Our observations illustrate that tool use in bonobos can be highly complex and no different from what has been described for chimpanzees. The only major difference in the chimpanzee and bonobo data was that bonobos of all age–sex classes used tools in a play context, a possible manifestation of their neotenous nature. We also found that female bonobos displayed a larger range of tool use behaviours than males, a pattern previously described for chimpanzees but not for other great apes. Our results are consistent with the hypothesis that the female-biased tool use evolved prior to the split between bonobos and chimpanzees.
Keywords: culture; great ape; neoteny; Pan; primate evolution; sex difference; tool use
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Zuberbühler, K. (2001). Predator-specific alarm calls in Campbell's monkeys, Cercopithecus campbelli. Behav. Ecol. Sociobiol., 50(5), 414–422.
Abstract: One of the most prominent behavioural features of many forest primates are the loud calls given by the adult males. Early observational studies repeatedly postulated that these calls function in intragroup spacing or intergroup avoidance. More recent field experiments with Diana monkeys (Cercopithecus diana) of Taï Forest, Ivory Coast, have clearly shown that loud male calls function as predator alarm calls because calls reliably (1) label different predator classes and (2) convey semantic information about the predator type present. Here, I test the alarm call hypothesis another primate, the Campbell's monkey (C. campbelli). Like Diana monkeys, male Campbell's monkeys produce conspicuous loud calls to crowned hawk eagles (Stephanoaetus coronatus) and leopards (Panthera pardus), two of their main predators. Playback experiments showed that monkeys responded to the predator category represented by the different playback stimuli, regardless of whether they consisted of (1) vocalisations of the actual predators (crowned hawk eagle shrieks or leopard growls), (2) alarm calls to crowned hawk eagles or leopards given by other male Campbell's monkeys or (3) alarm calls to crowned hawk eagles or leopards given by sympatric male Diana monkeys. These experiments provide further evidence that non-human primates have evolved the cognitive capacity to produce and respond to referential labels for external events.
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Briefer Freymond, S., Piovesana, L., Briefer. E. F., Beuret. S., Zuberbühler, K., Bshary, R., et al. (2015). Crib-biting behaviour of horses: stress and learning capacity. In Proceedings of the 3. International Equine Science Meeting.
Abstract: Crib-biting is a stereotypy in horses that is potentially linked to both chronic stress and genetic predisposition. Chronic stress can cause neurobiological changes such as alteration of the dopaminergic modulation of the basal ganglia [1]. These neurobiological changes could alter and modify the learning profile of the horses [2,3]. We tested 19 crib-biters and 18 non-crib-biting horses (controls) in five challenging spatial tasks, in order to test if differences in dopaminergic modulation impair learning capacities. The tests were performed in two time periods, in a small arena (8 x 10 m) that was familiar to the horses. For each trials, the horses were led to the start zone in front of a four-meter-long solid fence and were then left alone in the arena. Their task was then to find a bucket containing food, which was situated in different positions around the fence, depending on the tests. The time to reach the food bucket, the trajectory taken by the horse (left or right side of the fence) and the ECG trace were recorded continuously. Additionally, salivary cortisol was collected before the tests (baseline), after the first time period, and after the second time period. We found that crib-biters and controls behaved similarly during the learning tasks. However crib-biters that did crib-bite on the solid fence during the task (group A; 10 horses) behaved differently than crib-biters that did not crib-bite (group B; 9 horses) and controls (group C; 18 horses) for some tests, in their trajectory or time to reach the bucket. These differences are more likely explained by the time taken to crib-bite, than by differences in learning capacity. We did not find any difference between groups in their heart-rate variability (RMSSD). Yet, we found a difference in salivary cortisol after the first time period between groups A, B and C. Indeed, the crib-biters that did not crib-bite had higher salivary cortisol values than all the other horses (mean±SE: A, 0.51±0.16ng/ml, B, 0.78±0.17ng/ml, C, 0.59±0.20ng/ml; Linear mixed model (LMM), p<0.05). Our results suggest that crib-biting horses that did not crib-bite during the learning tasks were more stressed than all other horses. This difference could be due to higher stress sensitivity in crib-biters, which could be reduced by the opportunity to crib-bite. These results replicate our previous findings testing differences in cortisol levels between crib-biters and control horses during an ACTH challenge test. Therefore, crib-biting behaviour might be a coping strategy helping stereotypic horses to reduce their stress during frustrating situations [4].
Keyword: stereotypy, chronic stress, learning task |
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Wittig, R. M., Crockford, C., Langergraber, K. E., & Zuberbühler, K. (2014). Triadic social interactions operate across time: a field experiment with wild chimpanzees. Proc. R. Soc. Lond. B, 281(1779).
Abstract: Social animals cooperate with bonding partners to outcompete others. Predicting a competitor's supporter is likely to be beneficial, regardless of whether the supporting relationship is stable or transient, or whether the support happens immediately or later. Although humans make such predictions frequently, it is unclear to what extent animals have the cognitive abilities to recognize others’ transient bond partners and to predict others' coalitions that extend beyond the immediate present. We conducted playback experiments with wild chimpanzees to test this. About 2 h after fighting, subjects heard recordings of aggressive barks of a bystander, who was or was not a bond partner of the former opponent. Subjects looked longer and moved away more often from barks of the former opponents’ bond partners than non-bond partners. In an additional experiment, subjects moved away more from barks than socially benign calls of the same bond partner. These effects were present despite differences in genetic relatedness and considerable time delays between the two events. Chimpanzees, it appears, integrate memories of social interactions from different sources to make inferences about current interactions. This ability is crucial for connecting triadic social interactions across time, a requirement for predicting aggressive support even after a time delay.
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